Tag Archives: Plant Divisions

Plant Divisions: Gnetophyta

Ephedra cutleri

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

Gnetophyta Family Tree

Gnetum

Gnetum gnemon

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

Welwitschia

Drops of nectar on female cones - Barry Rice/CalPhotos/EOL

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

19th July 2013

31st August 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

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.

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Plant Divisions: Ginkgophyta

Ginkgo biloba

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

Ginkgophyta Family Tree

Leaves

Ginkgo biloba leaf

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

Ginkgo biloba with male cones

Cone on female Ginkgo

Cone on female Ginkgo

Ovules

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 fruit

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 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

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

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

Ginkgo biloba

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

Cones on Pinus armandii

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

Pine Cone

The Pinophyta Family Tree

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

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

Larch Cones

Araucariaceae—Araucaria family

Monkey Puzzle Tree - Araucaria araucana

Monkey Puzzle Tree – Araucaria araucana

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

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 Villarrica

Parque Villarica

Parque Villarrica, Chile

Parque Villarica, Chile

 Podocarpaceae—Yellow-wood family

Podocarpus acutifolius

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

Japanese Umbrella Pine Sciadopitys verticillata

Japanese Umbrella Pine Sciadopitys verticillata

 Cupressaceae—Cypress family

Cupressus

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

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

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

Dawn Redwood – Metasequoia glyptostroboides

Anicent Conifers

Thucydia mahoningensis

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

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

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

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

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

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

Sori on fern leaf

Fern gametophyte

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

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

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

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

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

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

Osmunda regalis

Hymenophyllales

Hymenophyllum caudiculatum Hymenophylllales Order

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

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

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

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

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'

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 Esplenium, Blechnum

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

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

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

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 Marchantiophytasee 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

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

Spikemoss, Quillwort, Clubmoss, Firmoss

Pictures taken from here:

Clubmoss

Some clubmoss  shapes

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

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

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

Spikemoss diagram

Quillwort

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

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.