Plant Families: Araceae (aka Aroids or Arums)

Zantedeschia Inflorescence

A Few Basic Facts

• Aroids are monocots in the family Araceae (aka arum family), in the order Alismatales. Most other families in this order contain tropical or aquatic plants, eg Hydrocharis and Saggitaria.
• Araceae has 104-107 genera. The largest genus is Anthurium with over 700 species.
• Location: Latin American tropical regions have the greatest diversity of aroids, however, they can also be found in Asia and Europe. Australia has only one endemic species – Gymnostachys.
• Habitat: Aroids can be aquatic (water), epiphytic (air) and terrestrial (ground). Most are tropical, but there are also arid and cold loving aroids.
• Distinctive features: All have an inflorescence (a structure containing a group of smaller flowers) which consists of a spadix (always) and a spathe (sometimes).

Aroid Flowers

• Aroids can be hermaphrodite (each flower is both male and female), monoecious (male and female flowers on the same spadix) or dioecious (male and female flowers on completely different plants).
• This family contains one of the largest flowers (Amorphophallus titanium, the titan arum) and the smallest (Wolffia, duckweed).
• Some aroid leaf and inflorescence shapes:

Aroid Leaf Shapes

Aroid Leaves

Aroid Fruits

Adaptations

Like many tropical families, aroids have evolved a number of adaptations to stay healthy and propagate. Some examples of adaptation:

• The spathe protects the flowers and in some cases is used to trap insects for pollination. It is not a petal, but a modified leaf. Many spathes turn green and photosynthesize after flowering has finished.
• Aroids have different types of roots adapted to their purpose. They have different adventitious roots  for climbing, attaching to rocks or taking in water.
• Many tropical species have shiny leaves to deter the mosses and lichens that grow in abundance in the rainforest.
• Smell is used by many species to attract pollinators. The smell of rotting meat, fungi and excrement is used for flies and beetles. Fragrant scents are used to attract bees.
• In many species the spadix actually heats up and can reach 25°C, even in near freezing conditions. This increases the release of smells to attract pollinators. The heat also makes visiting insects more active.
• Aroids that want to attract flies and beetles often have a warty, hairy, twisted appearance, with dark colours. This is to mimic the effect of dead animals, fungi or excrement.
• In some species, leaves may change shape from juvenility to adulthood – changing from variegated to unvariegated, pale red to green, or altering the number of lobes of the leaf. Colour change may deter animals from feasting on the fresh young leaves by making them look less leaf-like.
• Most species in Araceae have tubers or rhizomes, this means a damaged plant has the food storage and ability to grow new shoots from many points beneath the ground. Some aroids have other means of vegetatively propagating themselves, such as bubils and offsets.
• A number of aroids are poisonous, some are edible. Aroids have evolved poisons in some species as protection. Those that are edible did not evolve to be eaten by us, rather we have evolved to be able to eat certain plants.

Reproduction

Male and Female Flowers

Because many aroids are monoecious there is a danger of self-pollination. While self-pollination is easy (a guaranteed fertilisation), it leads to less genetic variety and less ability to adapt to changes in the environment. Aroids are particularly variable plants, in one small area of the Thai Peninsula 22 distinct varieties of the plant Aglaonaemia nitidum f. curtisii were found. However, in order to achieve this variation, the plant needs to cross pollinate reliably. It does this by being protogynous, meaning the female flowers on an inflorescence ripen first and then later male flowers produce pollen.

The Generic Process for Monoecious Aroids

A beetle, fly or bee (hopefully covered in pollen) is attracted by the scent given off by the heated spadix. The insect flies around inside the spathe, lands on the slippery surface and falls into the gap between the spadix and spathe. At this point only the female flowers are mature, and the  insect, made more active by heat from the spadix, moves about bumping into the flowers and depositing the pollen. Now, the insect has fulfilled the first part of its function, the aroid would like it to pick up pollen from the male flowers. However, the male flowers will not ripen for a day or so yet, so the insect needs to be held hostage. The slippery spathe ensures that the insect can’t escape, it is given sustenance in the form of nectar. Once the male flowers are ready and producing pollen, the slippery surface of the spathe breaks down, allowing the insect to escape. As it flies away it bumps into the male flowers, picking up more pollen to take to the next plant of the same species that it comes to.

Two Specific Examples of Monoecious Reproduction

Philodendron auminatissimum: Sometimes the pollinating insect can outstay its welcome, perhaps damaging flowers or laying eggs. This Philodendron has overcome the problem by shrinking the spathe after the male flowers have become active. This means that the beetle must leave or become crushed.

Arum nigrum: This arum doesn’t trap visiting flies, it merely confuses them. The hood of the spathe hangs over the spadix, obscuring the  sunlight, and there are translucent marking in the base of the spathe. When a visiting fly tries to escape, it heads for the light, but this just guides it deeper into the spathe. This leads to panicked and more active movement, ensuring pollination.

Arum nigrum

Reproduction in Other Aroids

In dioecious aroids the female flowers are found on a different plant to the male flowers, so a genetic mix is guaranteed. Not many aroids are dioecious, but a few species of Arisaema are.

A few aroids are even paradioecious and change gender to suit circumstances.

Hermaphrodite aroids are similar to monoecious ones, the male and female parts on each flower mature at different times so self pollination cannot occur.

Habitat

Arid

For the most part, arid aroids have not evolved the typical shrunken leaves and thickened cuticle of other desert plants. Instead they tend to grow under trees and bushes and at the base of rocks where a damp, shady microclimate allows them to survive. They have unusually lush foliage for arid plants. This would make them a target for being eaten, but they have dealt with this by producing harsh toxins and needles of calcium oxalate that pierce and poison the throats of animals. Animals know to stay well clear of aroids.

Some Examples

Heliocodicerous muscivorus

Heliocodicerous muscivorus: This is called the dead horse arum. It has an inflorescence 35cm long and wide. It grows in the shelter of rocks on a few islands on the Mediterranean. It is pollinated by either flies or beetles and grows where sea birds have their colonies at nesting time. Sea birds live in a mess of rotting fish and eggs, dead chicks and excrement, which attracts the flies/beetles. The arum must then compete with the smell of these, in order to attract those same insects for pollination. It mimics the dead not only in smell, but also by looking like the corpse of part of a horse, complete with tail. Visiting insects find themselves falling into where the ‘tail’ is and becoming trapped by the slippery walls. Many insects lay their eggs inside, although any maggots that hatch will likely starve to death. The insects are held for two to three days and are fed by nectar.

Note: It’s worth looking at photos of the dead horse arum, my painting doesn’t really do it justice.

Sauromatum venosum: This is the called the voodoo lily because it has the ability to flower without soil or water, using only the energy stored as starch in the corm. It smells rotten.

Stylochaeton lancifolius: This aroid has flowers and fruits half buried in the ground. I have been unable to find information about why this is. My suspicions are:

1.  It is pollinated by animals that are close to the ground. This can be seen in Aspidistra flowers, pollinated by slugs and snails. The flowers grow on the ground, under the leaves.
2. Being submerged provides a little protection, even if eaten or stepped on, the Stylochaeton still has half a flower remaining.
3. The fruits are eaten by something small. Having eaten the fruit, the seeds can be dispersed in the faeces.

Stylochaeton lancifolia

Tropical

Rainforests are dense, shady, and teeming with aggressive life. Animals, plants, fungi and bacteria are locked in a constant arms race. Consequently aroids have developed strong poisons, shiny leaves and the ability to climb to cope with some of these problems. In the tropics, latitudinal diversity (a wider variety of organisms that occurs close to the equator) means that it may be many miles through dense forest between plants of the same species. For this reason, aroids use very strong, and often unpleasant, smells to attract the right kind of insect.

A tropical rainforest has distinct layers and aroids grow in each of these. There are terrestrial aroids growing in the ground and epiphytic ones that climb into the canopy.

Climbers and epiphytes have only aerial, adventitious roots. There are two types: those that are sensitive to light and make for dark crevices where they can grip, and those that are sensitive to gravity and hang down from the plant in order to soak up rain and humidity.

Terrestrial Examples

Deiffenbachia grows in the Americas, while Aglaonema is native to Asia, they are both highly variable, but virtually indistinguishable from one another. This is an example of convergent evolution. Both contain toxins as a defence; Deiffenbachia is commonly known as dumb cane, because the if eaten, it causes the throat to swell, so that speech is impossible.

Aglaonema and Deiffenbachia – both highly variable, but in similar ways

 

Amorphophallus: This is a genus of tropical and subtropical aroids, native to Asia, Africa and Australasia. They attract flies and beetles by giving off the smell of rotting meat. Unusually, Amorphophallus species only put out one leaf or one inflorescence at a time, one a year. The single leaf is highly divided.

Some Amorphophallus inflorescences

Single, highly divided leaf of Amorphophallus

Some species in this genus also have white patches on the stem, these are to mimic lichen growing on trees and serve to protect them from stampeding elephants. When tramping through the jungle elephants have learnt to avoid trees, which are usually covered in lichen. Amorphophallus would be very easily damaged by an elephant, so by looking a bit more like a tree they can fool the elephant into avoiding them.

Lichen mimicking stem

Epiphytic Examples

Monstera

Monstera: These are one of the few plants to have holes in their leaves. Recent research shows that leaves with holes benefit in shady areas because the light coming through the trees is often dappled. By having holes in their leaves, Monstera cover a larger area with the same amount of leaf (so the same amount of energy used to make it) as a smaller leaf without holes. This allows the plant to take advantage of any sunlight that gets through the canopy.

Anthurium punctatum: This is an aroid from Ecuador. It has formed a symbiotic relationship with ants. It has nectaries away from the flowers because it is not trying to attract pollinators, but protectors. The ants set up home in the Anthurium and guard it from animals and insects that may eat it. However, in this Anthurium the ants are particularly aggressive and keep away pollinators also. The ants also secrete an antibiotic substance called myrmiacin, which is antibiotic and protects the ants from moulds and bacteria that might cause disease. However, this substance prevents pollen tube formation needed for the plant to be fertilised. These two barriers to pollination mean that the species can only propagate itself vegetatively.

Philodendron: This is a diverse genus. Plants can be epiphytic, hemiephytic or (occasionally) terrestrial. Hemiepiphytic means that the plant spends part of its life-cycle as an epiphyte (in the air). It may start off on the ground and then wind its way up a tree, then let its original roots die back. Or it may start as a seedling in the branches of a tree and a root will trail its way to the ground.

Philodendron bipinnatifidum

Temperate Woodland

Arisarum proboscideum

Arisarum proboscideum: aka the mouse plant. This is a woodland aroid, native to Spain and Italy. It has flowers like little mice. The ‘tails’ of these give off a mushroomy odor, that attract fungus gnats for pollination. The flowers have a spongy white appendage inside the spadix that looks like a mushroom to complete the deception. Fungus gnats often lay their eggs in the flowers, although the maggots won’t live to adulthood.

Aquatic

As I have blogged before, plants never evolved much in water. This means that all aquatic plants have evolved on land and then evolved again to cope with life in water. Some problems faced are – damage to flowers and leaves due to water currents, lack of access to pollinators, water blocking out light, lack of oxygen (leading to rotting roots), and the heaviness of water (800 times as dense as air) putting pressure on foliage.

Some solutions to problems:

• Aerenchyma:  these are gas filled cavities that improve buoyancy and oxygenation.
• Fish shaped foliage: these offer less resistance to water currents, so less damage occurs.
• Larger surface area in relation to volume: ie filmy leaves. This increases photosynthesis  eg Cryptocoryne
• Roots: These are not needed to transport water, since it can be taken in by all parts of the plant. However, roots are used to anchor the plant and stopped it being carried away by currents. eg Jasarum steyermarkii
• Reproduction: Many aquatic aroids find it easier to spread vegetatively rather than by flowering, in order to avoid flowering problems.

An Example

Pistia stratiotes: This is the only floating aquatic aroid, growing in swampy deltas in India and West Africa. It is adapted to staying still in fast moving currents, and has found the balance between sinking and blowing away.  The inner tissues have aerenchyma and the outer surfaces are ridged, velvety and with dense covering of hairs. This makes it unable to sink, and water repellent. Feathery roots act as an anchor. It has tiny flowers in a protective hairy spathe.

Pistias form a dense mat on the surface of the water, and can create mats of 15m wide. This makes Pistia something of a weed, causing problems to the ecosystem because the water underneath is deprived of light.

However, Pistia is not only harmful, some ecological benefits:

• The darkness caused by the Pistia mats has led to the evolution of blind elephantnose fish, which live beneath the mats. They hunt by electricity and have well developed brains and learning abilities.
• Birds and animals often make the floating island their home.
• Pistia can purify stagnant water.

 

Note: outdoor photos are mostly taken in Ecuador and indoor photos mostly from Wisley Gardens.

 

Plant Divisions: Flowering Plants

Leaf Variety in Magnoliophyta

Plants in the Magnoliophyta Division may also be called Angiosperms or flowering plants, they include grasses, palms, oak trees, orchids and daisies. Magnoliophyta is the only division that contains plants with true flowers and fruits, and all plants in this division use those flowers and fruits to reproduce. It is not known exactly when flowers first appeared, but definitely by 125mya and probably as far back as 160mya.

Flowers have proved to be an extremely successful adaptation, and despite its recent appearance, Magnoliophyta is by far the largest and most diverse plant division with over 250,000 different species and 500 families. (For comparisons to other divisions and their sizes see here)

Leaf Variety in Magnoliophyta

Flowers

In Magnoliophyta, flowers replaced the cones of more primitive plants, as a means of reproduction. Some flowers are brightly coloured, have a scent or produce nectar in order to entice animals to pollinate them, but others use wind or water and, having no need to draw attention, are barely noticeable.

Flower Variety in Magnoliophyta

Flower Variety in Magnoliophyta

Fruit and what that really means…

All plants in this Division produce fruits of some kind, even though what they produce may not be easily recognised as fruit. The botanical definition of a fruit is a matured ovary (the ovary is the female part of the flower that contains the ovules which become the seeds once fertilised), this includes peppers, tomatoes, aubergines, nuts, peas, wheat grains, but not apples or rhubarb. There is another meaning for the word fruit, which is culinary and refers to a sweet part of a plant that is eaten, this is the more familiar term and includes rhubarb and apples, but not tomatoes and nuts, etc. ‘Vegetable’ is only a culinary term, referring to parts of a plant used in savoury cooking, it may refer to any part of the plant: leaves (lettuce) flower buds (broccoli), stems (celery) or roots (carrots) and has no botanical equivalent.

Classification

Being such a large and interesting division means that the classification of Magnoliophyta has received more attention and undergone more changes than any other division.

How Many Flowering Plants Are There?

It was believed for some time that there were over 400,000 flowering plants, but it turns out that many species of plant (not known as yet how many) have actually been named twice or even three or four times. The binominal naming system (using two Latin names, eg Helianthus annuus) was designed to make plant naming international and straightforward, but with people all over the world discovering and naming plants and no comprehensive way of cross referencing them, we have ended up with a lot of confusion. Now, partly due to the international power of the internet, serious attempts are being made to work out how many actual species there are and to remove duplications. The Plant List is a collaboration between a number of botanical gardens around the world and has an impressive online collection of these names.

DNA Alters The Family Tree – Cronquist to APG III

Before DNA testing was possible (or DNA was known about) plants were collected into families, classes and orders according to detailed studies of how they looked.

Over the past few hundred years there have been many different classification systems, but one of the most commonly used and straightforward was the Cronquist System, devised in 1968. This System grouped plants into families, with the families grouped into orders, orders then grouped into sub classes and sub classes grouped into two classes: monocotyledons and dicotyledons. However, with genetic testing, it has been found that many of these groupings were wrong. A new system, called APG (Angiosperm Phylogeny Group), was introduced in 1998, but has subsequently been updated twice since then and will no doubt change in the future.

Frustratingly, what was once a very neat and straightforward system of classification has become an unwieldy, confused and messy system, because nature is never neat. The new system, called APG III, does not use classes and subclasses, instead it groups orders within clades, nested within other clades, nested within other clades; with some families not fitting into any clade at all.

The following diagrams are an attempt to show the changes in a simple manner, using images of plants to represent different orders and showing how those orders have altered their connection to others. It is clear that some assumptions were completely wrong, for example some dicots are more closely related to monocots than other dicots; the buttercup is not kindred with the water lily; cacti are more connected to Heuchera than originally thought and oak trees are closer to Euphorbia than London planes.

Cronquist system

APG III System

Key to Magnoliophyta plants

Note: I was unable to take photos of a tulip tree or Rhododendron in flower, so used photos I got online from here: Rhododendron and tulip tree

 

It was also fairly tricky to find all the necessary information about where plants appear in the Cronquist system, if anyone spots any faults, please contact me at the email to the right. Most of my information came from Wikipedia, and from here

To enlarge the key click the thumbnail

Anthurium and Ctenanthe – two flowering plants

Plant Divisions: Gnetophyta

Ephedra cutleri

Gnetophyta is a plant division containing only 3 genera and approximately 80 species. It isn’t known when plants in this division first evolved, but somewhere between 140 and 250mya. Although gnetophytes are gymnosperms, with no true flowers or fruits, they have some features in common with flowering plants:

• Vessel elements in the vascular system not seen in other gymnosperms
• Both Welwitschia and some Gnetum species are pollinated by insects
• Flower like structures on male cones of Welwitschia
• Nectar – produced on the tip of the cones rather than in a flower

All gnetophytes are evergreen and woody, and may be trees, vines or in the case of Welwitschia, difficult to classify. These plants have not been studied much and it is tricky trying to find out information about them. For example, although they are mostly considered dioecius (male and female cones on separate plants) all three genera sometimes produce bisexual cones, containing both stamen and ovules, but it isn’t really understood why, or if these cones can then reproduce.

Gnetophyta Family Tree

Gnetophyta Family Tree

Gnetum

Gnetum gnemon

There are 30-35 species of Gnetum, including two trees, many vines, and shrubs.

One tree, Gnetum gnemon, reaches 15-20m tall, and does not have fruits, but a fruit-like juicy covering for the seeds, which, like fruit, are edible to birds and aid in the spreading of seed.

Many Gnetum have seeds and leaves that are also edible to humans. Leaves of Gnetum have network of veins, something seen in dicotyledonous flowering plants, but no earlier evolved plants. All are dioecious. Gnetum are thought to be the first plants to be insect pollinated, by now extinct scorpion flies.

Welwitschia

Welwitschia

Drops of nectar on female cones – Barry Rice/CalPhotos/EOL*

There is only one species of Welwitschia and it only grows in the deserts of Namibia and Angola. Despite sometimes growing 10m wide (although more commonly 4m wide), Welwitschia has just two strap like leaves that grow continuously. The longest recorded leaves were 37m long, but most leaves break up in the harsh desert environment and become tatty and brown at the ends. Unlike Gnetum, the veins are parallel, as seen in monocotyledonous flowering plants as well as some ferns and cycads.  Welwitschia probably live 1000-2000 years, although this is difficult to know for sure. The female cones produce drops of nectar to entice insects to pollinate them. They have a single tap root grows deep into the sandy desert soil in search of water.

* Photo from The Encyclopedia of Earth with some more technical details about Welwitschia

19th July 2013

31st August 2013

I recently bought some Welwitschia seeds to see how they would grow. I planted them in a pipe to give space for the deep tap roots, 2:1 sand to compost. Within a week, three had germinated. Two died a few weeks later, I believe because I didn’t take into account that the single root only takes water from deep in the soil, so watering from above was pointless. I spray with fungicide every week or so. As can be seen from the pictures, Welwitschia has two cotyledons that start out orange and turn green.

Ephedra

Ephedra chilensis

There are about 50 species of Ephedra. They have slender stems with needle like leaves and small, sometimes brightly coloured, cones. They grow in dry areas in the Northern hemisphere, such as North Africa, Europe and North America. Ephedra looks very much like a gigantic version of psilotum (see previous blog about ferns) and can grow up to 3m. Some are monoecious.

The Evolution of Attracting Insects

While researching the previous blog about Ginkgophyta I learnt about terpenoids. Terpenoids are chemicals produced by both primitive plants (eg mosses and ferns) and flowering plants, the last group of plants to evolve. However, the function of terpenoids has altered as the plants have evolved. Terpenoids attract certain beneficial insects that feed on other insects that are harmful to the plant and this is an advantage to all plants, however, in later plants, Cycadophyta, Gnetophyta and Magnoliophyta, the insects attracted are also used to pollinate the plants and it was presumably because of the existence of terpenoids that such a partnership of plants and insects was able to form. Insect pollination is a far more efficient means of transporting pollen than wind, because an insect seeks out another plant, often a specific insect becomes an exclusive visitor to a specific plant. In the case of Welwitschia, growing in the desert, there may be many kilometres between plants, an awful lot of pollen would need to be produced in the hope of it being carried on the wind. Using insects to transport the pollen is akin to getting the postman to post a letter through the letterbox of the person you want to reach, instead of throwing  a thousand leaflets down the road they live in, in the hope they pick one up.

Plant Divisions: Ginkgophyta

Ginkgo biloba

Ginkgophyta is a plant division of non-flowering trees originating over 250 million years ago, in which all plants except for one, Ginkgo biloba, have become extinct. Ginkgo bilobas are large, deciduous trees with unusual looking cones and distinctive leaves, they can live for up to a thousand years. A few hundred million years ago whole forests existed around the world filled with different species of Ginkgos, but now the one remaining species is native only to China.

Ginkgophyta Family Tree

Ginkgophyta Family Tree

Leaves

Ginkgo biloba leaf

Ginkgo leaves are bi-lobed, tough and more resistant to decay than other leaves. Some leaves are borne on long stems and turn yellow, die back in winter, then reappear in spring, while others are on shorter stems that may survive the winter.

Trunk and Vascular System

The bark of Ginkgos is fissured and the trunks may reach to 4m in diameter.

The vascular system of Ginkgos, and also conifers, are different to that of flowering plants. While flowering plants have a series of tube-like cells to conduct water, Ginkgos have connecting cells with tiny perforations, these are valves that close when water is in short supply so that turgidity is preserved.

Reproduction and Survival

Ginkgo biloba with male cones

Cone on female Ginkgo

Ovules

Ginkgos are dioecious. The male cones grow from the shoot tip in clusters and release pollen. The female ovules (cones) appear in twos on the end of a stalk and do not look much like the cones of conifers. Each ovule has a drop of fluid, the pollination drop, that traps pollen to enable fertilisation.

Ginkgo pseudofruit

Ginkgo sperm cells are motile, swimming to the ovule using thousands of hairs. This is something that occurs in cycads too (see previous blog) and in ferns, but not conifers or flowering plants, so is  a throwback to a more primitive form of reproduction. Once fertilized the ovule grows into something resembling a fruit containing the seed.

Ginkgo seedling

Ginkgo seeds contain two cotyledons (seed leaves), but these never expand or emerge, instead they remain embedded in the seed providing nutrition for the seedling. The first leaves to appear above ground are true leaves with the distinctive Ginkgo shape, this is called hypogeal germination.

Ginkgos have a few clever ways of surviving and reproducing:

Like cycads, Ginkgos have been known to change sex, so that the male trees start producing ‘fruits’ and seeds. This is an effective way of propagating when there are no females around.

Ginkgos have a tendency to put out suckers from the ground that point upwards, but older trees sometimes also have odd downward growths, called Chichi, hanging from a single branch like stalactites. When these growths hit the ground they can start growing new roots and eventually form into a new tree, this is seems to be a form of reproduction for when the main tree is coming to the end of its life.

Chichi on Ginkgo

The brilliant photo above was taken by Rebecca Sweet and posted on Gossip in the Garden

If Ginkgos are hacked right back to the bare trunk they can regrow, either growing from the damaged stem or by putting out new shoots from the ground.

Ginkgos are also very resistant to pests, diseases, fires and pollution.

Medicinal Properties

Ginkgo biloba

Ginkgo biloba contains Flavonoids and Terpenoids which are naturally occurring chemical groups found in plants.

Flavonoids

Use for the plant: pigmentation, assisting in nitrogen fixation and cellular function

Use for humans: thought to have anti-allergic, anti-inflammatory, anti-microbial, anti-cancer and anti-diarrheal properties although this is not fully proved.

Terpenoids

Use for the plant: provide pigmentation and smell. They are thought to act as a deterrent to herbivorous insects and an attractant to insects that may eat herbivorous insects. They also are found in flowering plants and are used to attract pollinators. They may have antioxidant benefits for plants.

Use for humans: they have been used in traditional medicines for many years, although their effectiveness is not proved, they may have antibacterial properties and they may also have antioxidant benefits.

(note: I have been unable to ascertain exactly what Terpenoids and Flavonoids do in Ginkgo biloba specifically, so this information refers to their function in plants in general.)

Why do plants have medicinal properties?

We have enemies in common: plants have evolved chemicals that fight some of the same insects, fungi and bacteria that also plague humans.

Poisons can also be cures: mammals are often problematic for plants and so they have evolved ways to fight them off, but these ways may also, in small amounts, be cures. For example, Digitalis affects heart rate and is fatal in large amounts, but in small amounts can regulate heart rate.

While researching this question I have come across a common belief that plants evolved medicines in order to benefit humans, that by cultivating plants we made it beneficial for them to produce certain chemicals. However since plants first evolved 400 million years ago and evolved those chemical defenses millions of years ago, yet Homo sapiens only evolved a few hundred thousand years ago and only started cultivating plants 12,000 years ago, this isn’t really likely.

Further information about Ginkgos:

A very good website here, with clear pictures and video ( although the video is unfortunately difficult to hear):

http://kwanten.home.xs4all.nl/ovule.htm

Plant Divisions: Cycads

Cycas

Cycadophyta is a plant division that contains only trees, the cycads, which are palm-like gymnosperms. They first appear in the fossil record 280mya and haven’t changed much since then, although a fair few genera became extinct 200mya.

Cycads have long, narrow leaves, with either pinnate or bipinnate leaflets forming in a whorl at the top of a trunk or growing on slender stems from the ground. They vary greatly in size, with some reaching 18m high while others are only 30cm. Cycad leaves often unfurl as they grow and as lower leaves die their bases remain attached to the stem to form an armour-like casing. Like all gymnosperms, cycads do not produce flowers or fruits, instead they reproduce by cones.

Cycads appear in a geographical band that stretches from the Tropic of Cancer to the Tropic of Capricorn. They are mostly found in tropical and subtropical regions in both the northern and southern hemispheres, for example Central and South America. They can live up to a thousand years, but tend to grow very slowly.

Leaves

Leaves of Zamia furfuracea

All cycads are evergreens, with stiff long leaves. Many are pinnate (opposite leaflets along a central stem) or bipinnate (each pinnate leaflet divided into further leaflets). There is a little variety in the leaves of cycads, adult leaves can be blue-grey or green and they may be twisted or spiky. The veins in cycad leaves run in parallel lines from the leaf stem. Young leaves may be copper-coloured and in some genera they unfurl like fern leaves. Many cycads have stipules, these are small outgrowths at the base of the main leaf and can be useful in identification of plants. In general stipules can have different forms such as glands, hairs, miniature leaves, spines or scales, but on cycads they take the form of stunted leaf-like structures. In Bowenia and Stangeria the stipules are larger and fleshy, and their function is to protect the leaves as they grow.

Unfurling leaves of Cycas rumphii

Trunk and roots

Trunk of Encephalartos ferox

Cycad stems are often thick, but are not true wood, instead they are fibrous and contain a lot of starch. Many cycads, for example Bowenia and Stangeria, have subterranean stems, these are carrot-like. Cycads also have specialised roots, termed collaroid roots, that form into coral like structures. Coralloid roots contain blue green algae that form a symbiotic relationship with the plant, fixing nitrogen for it.

Subterranean Stem of Cycas

Reproduction

Cones of Dioon and Ceratozamia

It has recently been confirmed that cycads are pollinated by insects, which is rare for gymnosperms, but a distinct advantage for a plant that grows in tropical forests where there is little wind.

Cycads are dioecious which means that there are separate male and female plants, however cycads are one of the few plant groups that can change their gender, seemingly in response to stress such as physical damage or extreme cold. Plants are not as gender specific as mammals, (most are hermaphrodites) and although x and y chromosomes (the ones that differentiate gender) have been found in a few plants, the significance of these chromosomes in plants is still not fully understood.

Seeds with Red Sarcotesta in Female Zamia loddigesii Cone

When cycads are not changing gender, the process of reproduction is very similar to that of conifers, the male cones release pollen, the female cones receive the pollen and form seeds. However, being dioecious, the male and female cones do not appear on the same tree as they do with conifers. On many cycad genera, the seeds that form have brightly coloured seed coats called sarcotestae (sarcotesta singular). This is slightly fleshy and edible to birds and animals which aids in the spreading of seed and is a forerunner to fruit. (This can be seen in the picture to the right, with the red seeds forming beneath the brown scales, pushing them out as the seeds enlarge) Pomegranates and Ginkgos also have sarcotestae.

Male Cones of Ceratozamia, Chigua and Cycas

What is the difference between Cycads, Tree Ferns and Palms?

Cycads, tree ferns and palms can all easily get confused, all may have a central trunk, usually without side branches, and then a whorl of leaves at the top, consisting of a central rachis (the middle part of the leaf) with leaflets either side. All grow mainly in the tropics, although tree ferns can grow in more temperate areas too. However, the three types of trees are not closely related at all, each is in a different division, this can be seen most clearly in their very different ways of reproducing.

Palm Tree, Cycad, Tree Fern

Cycads – Cycadophyta Division – reproduce by pollen, cones and seeds.

Tree ferns – Pteridophyta Division – reproduce by spores and have separate sporophyte and gametophyte generations. Leaves are divided into distinctive fern leaf shapes. Trunks tend to have leaf bases still attached, same as with cycads, and their trunks are also not true trunks, however tree fern trunks are made of modified roots.

Palms – Magnoliophyta Division – reproduce with flowers and fruits. Palms are more varied than cycads and may have palmate or fan leaves, or a trunk with spikes or smooth bark.

Cycadophyta Family Tree

Cycadophyta Family tree

Cycadophyta is a small division with only three families and eleven genera. A number of genera are now extinct, for example Beania and Crossozamia.

Zamiaceae

Zamiaceae – Zamia pseudomonticola, Dioon purpusii, Encephalartos horridus

This is the family with the most genera – Chigua, Zamia, Ceratozamia, Macrozamia, Lepidozamia, Dioon, Encephalartos, Microcycas – and consequently the widest variety of shapes. The sarcotesta in this family are red, yellow or brown.

Zamia pygmaea is the smallest cycad and, at 30cm, is in fact the smallest gymnosperm.

Some species of Macrozamia have leaves so fine they look almost like pine needles or grass, whereas Zamia have wider leaves. Encephalartos has some species with distinctive spiky leaf shapes (see photo).

Ceratozamia with Female Cone

 Cycadaceae

Cycadaceae – Cycas seemannii

Mature Female Cycas cone with seeds forming

Cycadaceae contains only one genus Cycas. Although Cycas has many species, there is little variation in appearance, with all species having a stout trunk and a whorl of leaves at the crown. Cycas have notably different female cones to other cycads. The scales of the cones are open with seeds forming in between the scales, rather than underneath as in other cycads. The young leaves of Cycas are coiled (see near top for photo of unfurling leaves).

Stangeraceae

Stangeraceae – Stangeria eriopus

Stangeriaceae contains two genera, Bowenia and Stangeria. In this family, young leaves are coiled or folded. Stipules are present and the sarcotesta is purple. Most plants in this family have wider leaves than other cycads, although Stangeria paradoxa has leaflets as finely divided as a fern. Both genera have slender stems, with the trunk underground.

Bowenia spectabilis

Plant Divisions: Conifers

What makes conifers different to other plants?

All conifers, from pine trees to leylandii to yew trees, are within the Division Pinophyta (aka Coniferophyta). The number of species in this division is quite small, approximately 570 (although some estimates are higher), compared to 12,000 in the Bryophyta Division (mosses) or several hundred thousand in the Magnoliophyta Division (flowering plants). However, conifers make up a significant proportion of plant matter – about 34% of the total forest area – most of this is in the Northern hemisphere.

All conifers are woody, either shrubs or trees, and they are largely well adapted to cold conditions and acid soils. Most are evergreen; exceptions include the larch (Larix), two species of Cypress (Taxodium distichum, Taxodium ascendens) and the Dawn Redwood (Metasequoia glyptostroboides). Leaves are usually needle-like or scale-like, but there are a few with more strap shaped leaves. All are wind pollinated, evolving, as they did, long before brightly coloured flowers with nectar designed to attract insects. Some modern defining characteristics of conifers were not true of early conifers. For example in the Mesozoic era (252-66mya – a time when conifers were dominant and diverse) there were many deciduous conifers, some of which were not woody at all.

No conifers grow in lowland tropical rainforest, salt deserts or salt marshes, however they grow just about everywhere else; on mountains and in rainforests, deserts and arctic tundra. One conifer, Retrophyllum minus, is aquatic. None are epiphytes and only one is a parasite, Parasitaxus usta (Podocarpaceae).

Reproduction

3 Types of Cone on Pinus armandii

Conifers do not have flowers or fruits, but, do have pollen, unlike pteridophytes which reproduce by spores (see previous blog). Most conifers are monoecious which means they contain both male and female sexual organs on the same plant, but separately, as different cones. The male cones release pollen, the female cones receive the pollen and form seeds. As the female cone matures, it opens and the seeds are released, however this will only happen when it is dry so that the seeds will travel further not weighed down by rain. It is sometimes possible to see three different types of cone on one branch, the male, the juvenile female and the mature female containing the seeds. (The pictures below are close ups on the many individual seeds that make up the matured female cone.)

Pine Cone

The Pinophyta Family Tree

Pinophyta Family Tree

Pinophyta contains six to eight families, with a total of 65–70 genera.

Originally there were 4 different orders, but three are now extinct. The extinct orders are Cordaitales, Vojnovskyales and Voltziales; the extant order is Pinales.

Podocarpus and Pinus are the largest genera (but not that large) with Podocarpus having 108 species and Pinus having 109.

Pinophyta Families

There is some dispute as to how the division should be divided into families, I will concentrate on the seven most distinct families

Pinaceae—Pine family

Pinus montezumae

Pinaceae is the second largest family after Cupressaceae and is the last coniferous family to evolve, appearing approximately 150 million years ago, still a good 50 million years before flowering plants. It is mostly found in the northern hemisphere, in tropical to arctic environments. Pines have whorled branches and long needle-like leaves. The female cones are large and the male cones small. Larix and Pseudolarix are deciduous, the rest are evergreen. Whereas most conifers have two cotyledons (seed leaves), pines can have up to fifteen. Pines are aromatic and resinous – resin is a gum exuded from under the bark of the tree to seal over wounds or protect it from marauding insects as they damage the trunk. For the most part only conifers produce resin.

Larch Cones

Araucariaceae—Araucaria family

Monkey Puzzle Tree – Araucaria araucana

Araucaria araucana

Auracaceae is the second oldest family in Pinophyta, appearing 220mya. It contains very tall evergreen trees and is no longer native to the Northern hemisphere. The male cones are the largest of all conifer cones.  This family contains both the Monkey Puzzle Tree, Araucaria araucana and the Wollemi Pine, Wollemia nobilis.

Wollemi pine – Wollemia nobilis

Parque Villarica – The Monkey Puzzle Forest

Parque Villarica is in the Andes in Chile, it contains a spectacular section of forest at high altitude, consisting of almost entirely the Araucaria araucana and Nothofagus dombeyi – a deciduous tree, here without leaves, only white trunks.

Parque Villarica

Parque Villarica, Chile

 Podocarpaceae—Yellow-wood family

Podocarpus acutifolius

This is the oldest family of conifers, appearing 240 million years ago. It contains both trees and shrubs that have a variety of different leaf types from flat to scale-like to needle-like. Most are found in the Southern hemisphere, in the Oceana region and mostly in tropical environments. This family contains the world’s smallest conifer, Lepidothamnus fonkii which may be only 10cm tall when mature, although some can reach 60cm.

Sciadopityaceae—Umbrella-pine family

This family contains only one living species, Sciadopitys verticillata, known as the umbrella pine. This tree is native to Japan, a country with an especially diverse conifer population. While there is only one species, the tree has been cultivated and there are variagated, golden and columnar cultivars. The Umbrella Pine has cladodes instead of leaves, cladodes are modified stems and take the place of leaves on many cacti and on Butcher’s Broom.

Japanese Umbrella Pine Sciadopitys verticillata

Japanese Umbrella Pine Sciadopitys verticillata

 Cupressaceae—Cypress family

Cupressus

This is the largest conifer family and they are found throughout the world, it contains cypresses, junipers and leylandii. Trees in this family may have up to six cotyledons. For most plants in this family the leaves start out needle like on the juvenile plants and then become scale like as the plant matures.

Cephalotaxaceae—Plum-yew family

Cephalotaxus harringtonia

A small family with only three genera, found only in Asia and the USA. There is some debate about where it fits in the Pinophyta Division and it may eventually be combined with Taxaceae with which it has much in common. It has flat pointed leaves that sometimes curl a little and purple plum-like ‘fruits’ (see below for explanation of what these really are.)

Taxaceae—Yew family

Cunninghamia komshii

A family of evergreen trees with flat, sometimes curving leaves. This family contains the yew tree, which has seeds covered in red, berry-like flesh to attract animals, but while these are edible, the seeds are poisonous. In autumn it is common to see patches of red liquid containing yew seeds, these are where foxes have eaten the ‘fruits’ and thrown the seeds back up to prevent poisoning.

Dawn Redwood – Metasequoia glyptostroboides

Anicent Conifers

Thucydia mahoningensis

The oldest conifer family is Thucydiaceae, which first appeared 300mya, but is now extinct.   An early conifer was Thucydia mahonigensis (see left).

Conifers first evolved during an ice age and this explains why they are so adapted to cold – needles and scales allow snow to slide off them easily and since there is little sun with which to make new leaves, being evergreen is an efficient way of surviving.

Why some conifers have berries

Taxus baccata

As has been mentioned above, a number of conifers have fruit-like flesh surrounding their seeds, however, these are not real fruits. The botanical definition of a fruit is a matured ovary, usually with a seed inside it, but only Magnoliophyta Division (Angiosperms) plants have ovaries. The ovary, predictably, contains the egg, and when this egg is fertilised the ovary expands with sugars making it appealing to passing animals, the animals eat the fruit, carry the seed in their guts away from the parent plant and deposit it. This is highly advantageous for the plant since it allow the species to spread, but without ovaries, conifers had to find a different way to create tasty fruit-like organs to entice animals. The conifer families that have acheived this are: Taxaceae, Podocarpaceae, Cephalotaxaceae and Cupressaceae, and in the relevant trees, cones have been reduced, often producing only one seed and this is surrounded by enlarged bracts, that provide the colour and flavour. This distinction is irrelevant to the animals that eat the bracts and to the plants that succeed in spreading their seed, but is significant when understanding the difference between conifers and flowering plants.

The Parasitic Conifer: Parasitaxus usta

Parasitaxus usta

Parasitaxus usta is a woody shrub, less than 2m tall, that grows on the roots of only one other conifer, Falcatifolium taxoides, but has no roots of its own. Both are in the Podocarpaceae family and only grow in New Caledonia. Parasitaxus has purple scale leaves growing from small woody stems, like branches sticking out of the ground. Although the foliage and shoots of Parasitaxus have chloroplasts which are usually used for photosynthesis, the plant does not photosynthesize and instead extracts sugars from the host plants by means of a fungus. There may even be a direct connection between the vascular systems of each plant, since the parasite actually grows into the roots of the host. This parasitism is unlike any seen in angiosperms.

Further reading

http://www.conifers.org/index.php

Gymnosperms

The Division Pinophyta are part of a larger plant group called the Gymnosperms.

Gymnosperms consist of four different divisions: Pinophyta, Cycadophyta, Ginkgophyta and Gnetophyta. Unlike more primitive plants such as mosses and ferns, gymnosperms have seeds rather than spores, but they do not have flowers or fruits like more recently evolved plants, the angiosperms (aka Flowering plants or Magnoliophyta Division). Gymnosperm means ‘naked seed’, because the seeds are not contained in a matured ovary, or fruit. Most gymnosperms are wind pollinated, one exception being Welwitschia mirabilis (not a conifer, instead it is in the Gnetophyta Division, it will feature in a later blog)

Plant Divisions: Ferns and Horsetails

Dryopteris filix-mas

All plants in the Pteridophyta Division are known as ferns and most have the easily recognisable fern-shape, with fronds that unfurl to form distinctive self-similar shaped leaves radiating from a central point. These ferns are often grown in gardens and like shady areas with moist soil. Their leaves have also been used to demonstrate fractals, as explained here.

Dryopteris filix-mas

However there are a smaller number of plants in the Pteridophyta Division that have very different forms, some do not even have leaves, others look more like clovers than ferns.

What makes pteridophytes different to other plants?

Leaves

Pteridophytes differ from lycophytes (see previous blog about Lycopodiophyta Division) in that most have true leaves, called macrophylls. There are a few exceptions, such as Psilotales (see below) and horsetails (Equisetum).

Fern leaves grow by unfurling, starting off as tightly coiled balls. The manner of unfurling varies from species to species.

Unfurling Fern Fronds

Reproduction

Like lycophytes, pteridophytes have no flowers, using spores to reproduce. The spores are produced by sporangia. All plants have sporangia in one form or another, but in ferns these can be seen in clusters, called sori (singular: sorus). Sori on ferns are yellow, brown or black and are usually found on the backs of leaves.

Sori on fern leaf

Fern gametophyte

Also like lycophytes, the pteridophytes have a distinct sporophyte and gametophyte generation, with the sporophyte generation the dominant one, in ferns the sporophyte generation is the one with the leafy fronds. In lycophytes the sporophyte grows out of the gametophyte, the two are attached, however, with pteridophytes the gametophyte is a completely different plant. The fern gametophyte is only small, a few millimetres across, often growing under the ground and with primitive rhizoids instead of roots.

The Fern Family Tree

The Pteridophyta Division is made up of four classes and 10 orders (as always, these classifications vary from source to source, so I have chosen the most reliable system I can find). Of these, the Polypodiales Order is the largest, containing 80% of the world’s ferns, and also the most familiar, with all but a few of the ornamental ferns seen in gardens in Britain and Ireland.

Pteridophyta Family Tree

When researching distribution in Britain and Ireland, I found this website very useful http://www.ferns.rogergolding.co.uk/index.html

The Pteridophyta Orders

Psilotales

Psilotum nudum

These are tropical ferns and do not look fern-like at all. They do not have leaves, but small outgrowths called enations, – in leaves the xylem and phloem are inside the leaf, but in enations they are just beneath. Plants in this order do not have roots, but more primitive rhizoids (see previous blog: Mosses, Liverworts and Hornworts for more information). They consist of only two genera, Psilotum, aka Whisk ferns, with dark green stems and peanut-like sporangium, containing the spores; and Tmesipteris which has a more leafy, draping appearance.

Ophioglossales

Ophioglossum vulgatum

Like the plants in Psilotales, these are not very fern-like to look at. They consist of moonworts, adder’s tongues and grape ferns. These plants contain a lot of chromosomes, with one species, Ophioglossum reticulatum (looks similar to the Ophioglossum vulgatum seen right), containing a total of 1,260 (humans have 46 and most animals and plants have between 20 and 60). Although Ophioglossum vulgatum looks a little like an arum lily, it is not the same at all, the central part is not a flower, but the sporophyte. Their gametophytes live below ground and use fungi to obtain their food rather than using sunlight.

Equisetales

Equisetum

Equisetum is the only surviving genus of the Equisetopsida Class, but it is a diverse genus growing all around the world, some are even aquatic. About twelve different species grow in the UK. These plants have a a distinctive appearance, single green stems that photosynethesize to compensate for the leaves that are reduced in size. Over three hundred million years ago horsetails grew up to 30 metres high and helped to form the first forests.

Marattiales

Angiopteris

There is only one family in this order and all the ferns within it grow in the tropics. Some species have fern-like leaves, other have less divided leaves (see photo above). Some are giant with the fronds reaching up to 9m in length. Plants within this order can be recognised because their spore cases are fused together to form one long sorus. (see photo above)

Osmundales

Osmundales have been around for 210 million years, but only four genera are still living. They have fairly typical fern leaf shapes. Osmunda is the only fern that grows in the UK, it has photosynthetic fronds and non-photosynthetic, spore bearing fronds, which are brown, often referred to as flowers. Other than Osmunda, ferns in this order are tropical.

Osmunda regalis

Hymenophyllales

Hymenophyllum caudiculatum Hymenophylllales Order

These are known as the filmy ferns, their leaves are only one cell thick between the veins, which gives them a delicate, gauzy appearance, some have a typical fern-shape to their leaves, but others not. The sori are on the edges of the leaves rather than the back. Most are tropical, but some can be found in temperate rainforests. Three species have been found in Britain and Ireland.

Gleicheniales

Dipteris conjugata

These are tropical ferns, some with forked leaves arranged in a circle, others with fern-like leaves. There are only three families.

Schizaeales

Anemia rotundifolia

This order contains three families, with most species found in the tropics and a few temperate, although none in the UK. Ferns in this order have delicate leaves, some with ferny appearance. In this order is Lygodium, a climbing fern that has become a problematic weed in America. It has two different types of leaf – divided leaves containing the sporangia and entire leaf just for photosynthesizing, (picture here.)

Salviniales

Marsilea mutica

Ferns in this order are aquatic and mostly found in South America or Oceana. In this order are Azolla – the world’s smallest fern with leaves so tiny they look a little like duckweed; Marsilea that look like four leaved clovers (pictured) and pillwort that looks like quillwort, with thread-shaped leaves. Salviniales either float or grow in mud. Three species have been found in Britain and Ireland.

Cyatheales

Dicksonia antarctica Cyatheales Order

This order contains the tree ferns, one, Cyathea medullaris, can grow up to 20m. Tree ferns do not have wood and bark like other trees, instead they have modified roots growing above ground to form a mat that supports a slender stem, allowing the plant to grow tall. As shown below, tree ferns are often covered with hairs, and sometimes scales. All have typical fern-shaped leaves. The tree fern families are Cyatheaceae and Dicksoniaceae, Metaxyaceae and Cibotiaceae. Ferns in this order tend to be tropical, but a few are temperate. Dicksonia are sometimes grown in gardens in the UK but they need winter protection if the temperature drops below freezing. Cyathea have also been grown successfully in the UK.

Cibotium glaucum ‘Hapu Apulu’

Polypodiales

This order contains 80% of worlds ferns, 250 genera and 9,000 species. They grow everywhere except Antarctica.  Many have typical fern-shaped leaves, but not all (as seen in photo below). This is the order that contains most ornamental ferns found in gardens in the UK, for example – Adiantum, Blechnum, Woodsia, Polystichum, Onoclea, Matteuccia, Dryopteris, Asplenium (with entire leaves), Athyrium (Japanese Painted Fern) and some of these are native. Polypodiales also contains Pteridium, or bracken.

Matteuccia, Adiantum, Doodia
Asplenium, Blechnum

How old are ferns?

Ferns are often considered ancient plants, but while they do date back 350mya (first plants on land were 475mya, see previous blog about plant evolution for more information) all those families have died out now. There are a few ferns dating from 270mya that are still around now – Cyatheaceae and Dicksoniaceae, Gleicheniaceae and Hymenophyllaceae, but the vast majority of ferns only appeared about 75mya, around the time that orchids and lilies (both very recently evolved plants) appeared.

The Potato Fern

(Also written about in the Parasites Section of the Odds and Ends of Nature tab)

Potato Fern

Solanopteris brunei is the potato fern in the Polypodiales Order, it grows in Central and South America in the branches of trees. Ants colonize the ferns, living inside the potato like tubers and providing protection for the ferns in return.

This is a great web page about Solanopteris and Lecanopteris crustacea, another fern that has a symbiotic relationship with ants, some good photos. http://www.cpukforum.com/forum/index.php?showtopic=48907

Plant Divisions: Lycopodiophyta

Clubmoss Selaginella kraussiana

Plants within the division Lycopodiophyta are small, green, leafy and have spores but no flowers. They are a little like mosses, and many contain the word ‘moss’ in their common names. However, Lycopodiophyta evolved later than plants in the Bryophyta division and have a fully formed vascular system, with phloem and xylem, they are the earliest vascular plants to have evolved. There are about 2,000 species in total, and although they are more numerous in the tropics, they grow throughout the world.

There are, broadly speaking, four different types of plant within the Lycopodiophyta Division: clubmosses, firmosses, spikemosses and quillworts. The following diagram shows how they fit together in the plant kingdom. (click to enlarge)

Lycopodiophyta Family Tree

• Class – all end with ‘opsida’
• Order – all end with ‘ales’
• Family – all end with ‘aceae’

Of the four families within the Lycopodiophyta Division, Lycopodiaceae, the clubmoss family, is the largest and most diverse, containing between 13 and 19 genera. The spikemoss (Selaginellaceae) and quillwort (Isoetaceae) families contain only one genus each, although within those genera are many species.

Note: Lycophyte is a general term for plants in the Lycopodiophyta Division.

What makes lycophytes different from other plants?

Leaves

Lycophytes are distinct from most other plants, by having microphylls, a primitive form of leaf. Microphylls are a few evolutionary steps on from the leaves of BAMs (Bryophyta, Anthocerophyta and Marchantiophyta– see previous blog) which are mostly one cell thick and without specialization. Microphylls can be many cells thick, with special cells for the epidermis and vascular tissue. They are not necessarily small – extinct Lepidodendron had microphylls over a metre long – but they are simpler than normal leaves, which are called megaphylls. Whereas megaphylls have a complex network of veins, or a number of veins running from base to tip, microphylls have a single, unbranched vein.

Horsetails (a type of fern) also have microphylls, but from the fossil record it looks as if they evolved megaphylls and then reverted to microphylls later.

Reproduction

See previous blog Plant Divisions: Mosses, Liverworts and Hornworts for more information about gametophytes and sporophytes.

Like BAMs (Bryophyta, Anthocerophyta and Marchantiophyta), lycophytes have alternating generations. The sporophyte stage produces spores and these grow into the gametophyte stages which produce sperm and eggs which then fuse to form a new sporophyte. However, there are a few important differences.

One difference occurs only in spikemosses and quillworts. BAMs, clubmosses and firmosses are homosporous, which means that all spores produced look identical and only become apparently male or female when the spores become gametophytes. Spikemosses and quillworts  are heteropsorous, meaning they produce two types of spores that look very different: large megaspores (female) and small microspores (male).

Heterosporous Reproduction

Selaginella – Heterosporous Reproduction

A fertile cone grows out from the sporophyte (the sporophyte is the main body of the plant, the part that has leaves), from this grow sporangia that contain spores, some the male microspores, others the large female megaspores.  When these spores are released they become separate, tiny plants, the gametophytes. The male gametophyte releases sperm, the female contains eggs. The sperm find and fertilise the egg by swimming to it after it has rained. The new sporophyte then grows out of the female gametophyte, putting down roots and growing leaves, becoming a whole new plant.

Other Differences in Reproduction

• The female gametophyte generation has rhizoids, the more primitive form of root, while the sporophyte generation has roots
• The sporophyte generation is the larger, longer lasting stage; in BAMs it is the gametophyte stage
• Unlike BAMs, the gametophyte generation is completely removed from the sporophyte generation. In some lycophyte species gametophytes grow on the surface of the ground, others grow in water.

Different Types of Lycophytes

Spikemoss, Quillwort, Clubmoss, Firmoss

Pictures taken from here:

• Spikemoss: Wikipedia
• Quillwort: Wikimedia
• Clubmoss: Saluda Shoals Parke Rangers Blog
• Firmoss: Wikimedia

Clubmoss

Some clubmoss shapes

Clubmosses are in the Lycopodiaceae family, they have needle-like or scale-like leaves, a few of the different leaf shapes can be seen above. They are the most varied within the Lycopodiophyta Division, descibed as having between 13 and 19 genera and somewhere between 400 and a thousand species. Although most clubmosses are only a few centimetres high, and green, there are a few exceptions, for example Lycopodium deuterodensum, that grows in Australasia, can reach a metre high and Lycopodium fastigiatum, native to New Zealand, is orange in colour.

Clubmosses usually have a creeping or epiphytic habit (grow on other plants, or sometimes inanimate objects, high up). Most grow in tropical mountains, but they are found throughout the world, including in the UK. Clubmosses are homosporous and although their reproductive lifecycle is similar to the one shown above, the male and female spores are the same size and shape.

Firmoss

Firmoss

Firmosses are in the Huperziaceae family. They are mostly epiphytic and grow throughout the world. There are over 400 hundred different species of firmoss, although their appearance does not change much from one to another. They are more upright than clubmosses tend to grow in clusters, looking like a small fir tree forest. They are also homosporous.

Spikemoss

Some spikemoss shapes

Spikemosses are contained in one genus, Selaginella, but there are still a number of different leaf shapes within the 700 or so species. In the US it is sometimes grown as a houseplant or as ground cover. It is heterosporous having both micro and megaspores.

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Spikemoss diagram

Quillwort

Quillwort

Quillworts are in the order Isoetales, which, like the spikemoss order, has only one family and genus, but about 150 species. Most are aquatic or semi-aquatic plants. Some species have been found off the coast of Scotland. The leaves are narrow and grasslike and it is difficult to distinguish from grass without a microscope. It is heterosporous.

A website tracking lycophytes in the UK is here http://www.ferns.rogergolding.co.uk/ferngenus/isoetes/echinospora.html

Extinct Species

Sigillaria and Lepidodendron Trees

Originally Lycopodiophyta contained three other orders: Lepidodendrales, Pleuromeiales in the Isoetopsida class and Drepanophycales in the Lycopodiopsida class. Plants in these three orders grew metres high, some up to 30m high, and formed forests in the Carboniferous Period 300-350mya. Tree ferns and early conifers also grew in Carboniferous forests. Coal formed from the decaying plant matter in these forests.

Plant Divisions: Mosses, Liverworts and Hornworts

Bryophytes used to be a general term for mosses, liverworts and hornworts, and these three were grouped together into a single division due to their similarity. It is now known that they are not closely related and they have been split into three separate divisions.

• Bryophyta Division – mosses

• Anthocerophyta Division – hornworts

• Marchantiophyta Division – liverworts

Although the term bryophyte is still used to mean plants in all three divisions, including Bryophyta, I think that is confusing, so instead I will use “BAMs” (Bryophyta, Anthocerophyta and Marchantiophyta) to refer to the three divisions, and the plants within them.

Moss

Introduction

BAMs (Bryophyta, Anthocerophyta and Marchantiophyta) were some of the earliest plants to evolve, as a result they are primitive when compared to later, vascular plants. Their leaves, stems, and the rhizoids they have in the place of roots, are all simpler and less effective. BAMs are non-vascular, although they do have a simple, conducting system for transporting water and nutrients, it does not contain the xylem and phloem vessels found in vascular plants and is not nearly so efficient. As a result, BAMs do not grow large, because they cannot transport water a long distance, and are limited to damp shady areas, because in the sun  they dry out. They reproduce by spores, rather than seeds and their reproductive cycle involves two distinct, external stages, (essentially two different plants) which does not happen in plants with seeds.

Mosses can be divided into two different groups:

• Acrocarp – upright
• Pleurocarp – creeping

Leafy and Thallose

And Liverworts:

• Thallose – larger rubbery leaves and flower-like capsules containing spores (sporophytes). Thallose means the tissue is undifferentiated.
• Leafy – smaller leaves arranged along a short stem, small globe capsules. Most liverworts are leafy.

The Hornwort Division is much smaller and does not split readily into types.

Note: Plants in the Ceratophyllum genus are also referred to as hornworts, these are very different plants and they are aquatic and flowering.

Moss with Sporophytes (capsules and seta)

What makes BAMs different from other plants?

Click for close up

Roots and rhizoids: BAMs do not have roots, they have rhizoids, these are also found on horsetails and ferns (Pteridophyta), club mosses and quillworts (Lycopodiophyta). Some fungi and algae also have rhizoids. Rhizoids are similar to roots, in that they transport water and nutrients, and anchor the plant to the soil or substrate, but are much simpler in form, often only one cell thick.

Click for close up

Simple and Complex Leaves: Leaves on BAMs are single celled, apart from the midrib. They contain chloroplasts for photosynthesis, but otherwise the cells are not specialised as they are in other plants.

Reproduction

To explain how sexual reproduction is different in BAMs, it’s necessary to first explain sexual reproduction as it is in all organisms.

Diploid and Haploid Cells

There are two types of cell:

• Diploid cell (2n) –  a cell with two sets of DNA, most cells in an organism are diploid.
• Haploid Cell (n) –  cell with one set of DNA, cells are only haploid when an organism is reproducing or preparing to reproduce.

And two types of cell division:

• Mitosis – a cell replicates its DNA and splits in two so that each new cell has the same amount of DNA as the original. This type of cell division is used when an organism grows. Can occur in both haploid and diploid cells.
• Meiosis – the DNA does not replicate and when the cell splits in two each new cell has half the DNA of the original. This type of cell division is used only for sexual reproduction. Occurs only in diploid cells and results only in haploid cells.*

Diagram Showing Mitosis

Diagram Showing Meiosis

Example: Daisy

Inside the flower of a daisy, some cells are dividing by meiosis in order to create haploid cells, called the male gamete. These haploid cells form pollen (each pollen grain contains one gamete) which are picked up by bees and deposited onto another daisy flower that will contain the female gamete. The two haploid gamete cells fuse to form a single diploid cell (one strand of DNA from each gamete), called the zygote. The zygote grows by mitosis in the flower until it forms a slightly larger and more complex embryo daisy. This embryo is contained within a seed which falls (or is blown) away from the mother plant to land and grow, by mitosis, into a new daisy, similar but not identical to the two parents.

This process is fairly similar in animals with the same use of meiosis and haploid cells to reproduce, the main difference is in how the male gamete finds the female gamete (eg by mating) and instead of falling as a seed the embryo is released as an egg, a pupa or forms inside the adult.

Diagram of Moss

BAMs do not reproduce in quite the same way. Although they too create haploid cells by meiosis (called spores), these haploid cells form a plant called a gametophyte. The gametophyte is made of haploid cells and creates more haploid cells, the gametes, by mitosis. Some gametes are male, some female (although some species produce only male or female gametes and these gametes will need to find a gamete of the opposite gender to fuse with). A female gamete fuses with a male gamete to create a new diploid plant, called a sporophyte. Often the sporophyte grows out of the gametophyte (seen right). The sporophyte produces spores, these are haploid and each will potentially grow into a new gametophyte and so the cycle starts again.

This alternation of diploid and haploid plants, sporophyte and gametophyte, is called Alternation of Generations. It is often described as happening in all plants, but only plants, never animals (although it can also be said to happen in fungi). However, animals do have a diploid and haploid phase, the only real difference is that plant gametes, such as pollen can divide, whereas haploid gamete cells in animals cannot. Otherwise the process is very similar: diploid cells divide by meiosis to become haploid gametes and two gametes of different genders fuse to become a diploid zygote which then divides by mitosis to get bigger and become a whole new organism. Thank you to Walter Hintz at this website for helping me understand this http://www.allexperts.com/user.cgi?m=4&expID=48818&catID=664

Here are my question and his answer.

http://en.allexperts.com/q/Biology-664/2013/3/alternating-generations.htm

What makes BAMs different from each other?

Yellow Moss

All BAMs like moist shady areas, but mosses are a little hardier than liverworts and cope better with dry weather.

There are 12,000 species of moss, 6,000-8,000 species of liverwort but only 100 species of hornwort. Mosses are abundant in England, liverworts are a little harder to find and hornworts are not common here, preferring tropical climates.

Liverwort and Pencil Tip

I took a recent trip to Highgate Cemetery to find mosses and liverworts. I found a few liverworts in the really boggy areas, growing on soil, although liverworts can grow on stone. I was surprised at how small the liverworts were and the photo above shows some with a pencil tip to show size. Moss covered everything, but at first it was difficult to see any more than one kind – partly because I wasn’t used to looking and partly because certain mosses are much more successful than others and tend to take over. In the end I did spot a few different kinds, the photos throughout this blog are ones I took on the trip, but here are some close up photos of the different types of moss I discovered.

Mosses Found In Highgate Cemetery

Differences in Appearance

Liverwort

Mosses are soft and leafy, with many tiny leaves, and the sporophytes are small capsules on the end of long thin seta (seen in diagrams above). Liverworts have slightly larger, flat rubbery leaves usually growing much closer to the ground, their sporophytes are either like rubbery, green flowers (seen on the drawing at the top of this page) or globes on a stem (seen below). Some liverworts have round gemma cups (seen at the top of this photo) containing fragments of liverwort that can break away and form new gametophytes, this is a form of asexual reproduction. Gemmae can also be found in mosses. Hornworts look fairly similar to liverworts in the gametophyte stage, but the sporophyte is a distinctive long, thin, needle-like protuberance.

Liverwort with Sporophytes

Differences in Biology

The biological differences are a little detailed for the purposes of this blog, so I will only list a few briefly: Hornworts produce slime in between the cells. Most hornwort species have a single chloroplast in each cell, unlike liverworts, mosses and all other plants, only algae have this same feature. The rhizoids in mosses are multicellular, but unicellular in hornworts and liverworts. Mosses and hornworts have true stomata (breathing holes) on their sporophytes, but liverworts do not.

Bizarre bryophytes and not-bryophytes

Spanish Moss

Spanish moss or beard lichen is often thought to be a parasitic, but it merely grows in abundance on trees. However, it is NOT actually a moss, or a lichen, but a flowering plant in the bromeliad family. Ball moss is similar, a flowering plant rather than a moss. Reindeer moss is also not a moss, but a lichen.

This picture was taken from the following website http://www.learnnc.org/lp/multimedia/6540

Mosses are not parasitic, but some liverworts are. Aneura mirabilis, Cryptothallus mirabilis and Cryptothallus hirsutus are all parasitic liverworts. They are pale because they have no chlorophyll and therefore cannot photosynthesize. Instead they gain their nutrients from fungi that are working symbiotically with a tree, ie the fungus and tree are aiding one another, the tree provides carbohydrate for the fungus, the fungus extracts nutrients from the soil for the tree and then the Aneura sneaks in and takes nutrients from the fungus without giving anything back.

Luminous Moss

Luminous moss (Schistostega pennata), also known as Elfin Gold, glows green in the dark. It can take light, no matter how faint, and reflect it, leading to the luminescence. For this reason it is able to grow in places too dark for other mosses. It is native to the Northern Hemisphere and is found growing in caves or between rocks. This picture is taken from http://www.botanic.jp/plants-ha/higoke.htm and there are other pictures of the moss on that site.

*Note to meiosis: Occasionally, or with some specific species, the process of meiosis and mitosis do not occur as described above, and instead a cell, a tissue, or an entire organism can end up having more than two sets of DNA. For example if a diploid cell does not split by meiosis as usual and then fuses with a haploid cell, the result is a cell with three sets of chromosomes. This state is called polyploidy, it can have a function, both biologically and commercially.

Plant Divisions

The kingdom Plantae is split into ten divisions:

• Anthocerotophyta
• Marchantiophyta
• Bryophyta
• Lycopodiophyta
• Pteridophyta
• Gnetophyta
• Cycadophyta
• Ginkgophyta
• Pinophyta
• Magnoliophyta

Occasionally algae are included as a further two divisions Charophyta and Chlorophyta, but recent research classifies these as too primitive to be called plants. See Kingdom blog for more information.

Another division is Pteridospermatophyta, these are seed ferns dating from the Devonian period, and have died out.

Plant Divisions

Non vascular – plants without a proper system for transporting water through the plant, as a result these are small plants that need damp shady areas to live in. These were the earliest plants to evolve.

Vascular – plants that have a proper system for transporting water and sugars around the plant. The vascular system itself has continued to evolve, with Gnetophyta having a more evolved system than other Gymnosperms and Magnoliphyta having the most evolved system.

Spores – spores are a primitive form of reproduction.

Gymnosperms – seed producing, but the seeds are not contained in an ovary and there are no flowers . All are woody.

Flowering plants – no plants outside of the Magnoliophyta Division flower and this was the latest plant organ to evolve. Flowering plants account for most plants in existence (about 80-90%).