Tag Archives: Science

RHS Level 3: Plant taxonomy, structure, and function

  1. Understand the Plant Kingdom and the taxonomic hierarchy.

1.1 Describe the major groups of the Plant Kingdom.

List the main groups within bryophytes, pteridophytes, gymnosperms and angiosperms.

This is quite an archaic way of grouping plants. The kingdom Plantae is usually divided into 10 divisions, listed below, with the groups in the syllabus in bold. Gymnosperms consists of Pinophyta, Cycadophyta and Ginkgophyta. Angiosperms = Magnoliophyta:

  • Anthocerotophyta – hornworts
  • Marchantiophyta – liverworts
  • Bryophyta – mosses
  • Lycopodiophyta – club and spike-mosses
  • Pteridophyta – ferns and horsetails
  • Gnetophyta – 3 extant genera of woody plants
  • Cycadophyta – cycads
  • Ginkgophyta – Ginkgo
  • Pinophyta/Coniferophyta – conifers
  • Magnoliophyta – flowering plants
divisions-for-rhs

Plant Characteristics

Describe and compare the structural and reproductive characteristics of: mosses, ferns, conifers and flowering plants in relation to their adaptation to terrestrial life.

DETAILS OF ALTERNATION OF GENERATIONS AND HAPLOID/DIPLOID STRUCTURES ARE NOT REQUIRED.

I’ve written about these four groups previously, the information about structural and reproductive characteristics is in the first two paragraphs of each blog

  1. Mosses
  2. Ferns
  3. Conifers
  4. Flowering Plants

Brief description of reproductive characteristics:

Bryophytes – have sporophyte and gametophyte stages. Gametophyte is dominant.

Pteridophytes – have sporophyte and gametophyte stages. Sporophyte is typical fern, gametophyte is small and rarely noticed.

Gymnosperm – have male and female cones. Male cones drop pollen which is carried by wind.

Angiosperm – have flowers that may be dioecious, monoecious or hermaphrodite. Usually wind or insect pollinated (but other methods of pollination exist).

1.2 Describe features of plant classification and nomenclature relevant to horticulture.

State the hierarchy of botanical units and explain how and when they are used.

To include: family, genus, species, subspecies, varietas, forma.

To include ONE NAMED plant example for EACH of the above terms showing how it is written.

Family

Have the ending -aceae (many family names were recently changed to conform to this). Plant families are usually named after the biggest or most well known genus in that family. eg Euphorbiaceae, the family that the genus Euphorbia is in.

Genus

Genus is a subdivision of family. The genus of a plant is used as the first part of its binomial name, and is always capitalised. It should be written in italics (or underlined). eg Euphorbia.

Species

Species is a subdivision of genus. The species of a plant is used as the second part of its binomial name and is never capitalised. It should be written in italics (or underlined). eg characias  (as in Euphorbia characias.)

Subspecies

Recommended abbreviation is subsp. but ssp. is sometimes used. Subspecies are written in small italics, but the word subsp. is not. A subdivision of species. Plants within different subspecies but within the same species are capable of interbreeding, but don’t due to geographical separation. eg Euphorbia characias subsp. wulfenii.

Varietas

A subdivision of species, similar to subspecies (and the two terms often overlap) however, different varieties within a species may geographically overlap, unlike subspecies. Recommended abbreviation is var. Varieties are written in italics, but var. is not. eg Malva alcea var. fastigiata.

Forma

If a plant shows uncharacteristic appearance of its species (such as habit or colour) then it can be known as a different form. These differences are usually due to environmental reasons and won’t be passed to the next generation. Recommended abbreviation is f. The form is written in italics, but f. is not. eg Vinca minor f. alba.

Explain the meaning and use of the terms: cultivar, Group, trade designation (selling name), Plant Breeders’ Rights, interspecific, intergeneric and graft hybrids, naming authority.

To include ONE NAMED plant example for EACH of the above terms, showing how it is written.

Cultivar: This is short for ‘cultivated variety’ and refers to plants that have been bred for their characteristics. The names are often chosen as a selling point, for example using somebody’s name, making them a good present for people of the same name. eg Clematis ‘Willy’ (note the cultivar name is capitalized, in single quotes and not italicized. Because of the complexity of cross breeding across species, the species of a cultivar is only sometimes used.)

Group: If several cultivars are similar, they can be grouped together to make customer selection easier. eg Lilium Darkest Red Group (note the group is capitalized, not italicized, and not in quotes.)

Trade designation: Cultivar names cannot be legally protected. If a plant breeder wishes to keep sole legal rights to a plant, then he/she uses a trade name. This a commercial synonym that is legally protected. eg Rosa FASCINATION = Rosa ‘Poulmax’. (note: the writing method for ‘Fascination’ changes, sometimes it is in quotes, like a cultivar; other times it is in square brackets. The correct notation is all in capitals, not italicized, not in quotes, often in a different font.)

Plant Breeders’ Rights: Breeders using a Trade designation have Plant Breeders’ Rights which are recognised internationally. If you own the rights to a cultivar, it cannot be bred by anyone else without your permission. If somebody buys one specimen of your cultivar, you still have exclusive rights to all propagation material of that plant: seeds, cuttings etc.

Interspecific, intergeneric and graft hybrids: Unlike with animals, plants can be bred across species and genera. Plants of different genera can, in some cases, be grafted together, occasionally this will lead to a mixing of cells where the scion and the rootstock meet, this is not a true hybrid. It is also known as a graft chimaera.

examples

  • Interspecific hybrid –  Mahonia × media (bred from Mahonia lomariifolia and Mahonia japonica, note the ‘x’ in the middle and new specific epithet.)
  • Intergeneric hybrid× Cupressocyparis leylandii (bred from Cupressus macrocarpa and Chamaecyparis nootkatensis, note the ‘x’ at the beginning and the genus which is a combination of the parents’).
  • Graft hybrid – +Laburnocytisus ‘Adamii’, (a graft hybrid between Laburnum and Cytisus, note the ‘+’ at the start and genus which is a combination of the parents’.) This graft contains flowers of Laburnum and Cytisus (ie both yellow and purple) but also flowers that are a pinky colour, a mix of the two.

Naming authority: The International Cultivation Registration Authority is a naming authority, responsible for seeing that cultivar names are not duplicated.

State the significance of the ICN (The International Code of Nomenclature for algae, fungi and plants) formerly ICBN (International Code of Botanical Nomenclature) and the ICNCP (International Code for Nomenclature for Cultivated Plants) in the naming of plants.

The ICN (The International Code of Nomenclature for algae, fungi and plants) A code that governs plant discoveries in the world – ensuring that plants aren’t given different names by different discoverers, or that already named plants aren’t given new names without reason.

International Code of Nomenclature website Contains complex set of rules to standardise naming and classification eg changing all plant families to end in -aceae, Compositae > Asteraceae.

ICNCP (International Code for Nomenclature for Cultivated Plants) – a code that governs the naming of newly created cultivars.

Cultivated Plant Code

Explain the reasons for name changes: reclassification (scientific research, new discovery), changes in nomenclature (rule of priority), incorrect identification.

To include TWO NAMED plant examples for EACH.

Reclassification (scientific research, new discovery)

  1. With advances in DNA technology, African Acasias were found to not be related to Australian Acasias. Australian Acasias have kept their name, while African have become Vachellia or Senegalia.
  2. Coleus became Solenostemon, but was then found to be part of the Plectranthus genus. Plectranthus scutellarioides used to be Coleus blumei.

Rule of priority

This is where a plant is discovered to have been named previously, and its old name is found on record. When an existing name is discovered, the plant should revert to this name, but occasionally, if the new name is far more familiar it will be kept.

  1. Platanus ×acerifolia was the name of the London Plane, but this name was recorded in 1805 and it was discovered later that an earlier name of Platanus ×hispanica had been recorded in 1770. Therefore Platanus ×hispanica became the official name.
  2. Festuca subgenus Schedonorus was moved to the genus Lolium and its name became Lolium subgenus Schedonorus.

Incorrect identification

Sometimes a name change is due to a simple mistake, when one plant becomes mixed up with another.

  1. Archontophoenix cunninghamiana was for a long time incorrectly sold as Seaforthia elegans.
  2. Syzygium australe was often sold as Syzygium paniculatum

 Explain how plant names can indicate: plant origin, habitat, commemoration, colour, growth habit, leaf form.

To include TWO NAMED plant examples for EACH. 

It is often the plant species that indicates origin, colour etc, but not always (see below). The Latin will only refer to one characteristic (when Latin plant names were first used, botanists tried to include every characteristic, leading to ridiculously long names, then Linnaeus reduced it to two).

Plant origin: Mahonia japonica (Japan), Arum italicum (Italy)

Habitat: Clematis alpina (alpine plants), Pinus sylvestris (wood or forest)

Commemoration: Photinia fraseri (John Fraser1750-1811 nurseryman), Weigela (Christian Weigel 1749-1831 German botanist)

Growth: Briza maxima (large or largest), Vinca minor (smaller)

Habit: Cotoneaster horizontalis (growing horizontally), Phlomis fruticose (shrubby)

Leaf form: Acer palmatum (palmate leaves), Ilex aquifolium (pointed leaves)

Plant Families: Araceae (aka Aroids or Arums)

Zantedeschia Inflorescence

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).
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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 Leaf Shapes

Leaves

Aroid Leaves

Fruits

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

IMG_4023

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

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

Dead Horse Arum

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

Stylochaeton lancifolia

Tropical

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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.

Ag 2

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.

IMG_4021

Some Amorphophallus inflorescences

IMG_0352

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.

IMG_0357

Lichen mimicking stem

Epiphytic Examples

IMG_0770

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

Philodendron bipinnatifidum

Temperate Woodland

Arisarum proboscideum

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 2.JPG

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.

 

Fasciation

Normal Flower and Fasciated Flower

Normal Flower and Fasciated Flower

Fasciation in plants is a bizarre mutation in the meristem (growing point) leading to flattened flower stems and distorted flowers, fruits and roots. It can also lead to a ring of small flowers surrounding the main flower, this is known as ‘hen and chicks’ and can be seen in some of the Veronicastrum pictures below. The meristem is where cells actively divide in order to grow or create new flowers and leaves, a disturbance to this process can lead to the cell division intensifying and occurring in a haphazard manner, leading to distortion. Essentially the growing point ceases to be a point and instead forms a cockscomb. For many plants this is most commonly noticed with flowers, which then go on to form distorted fruits, but with cacti and ferns it is often seen in the leaves.

Causes

Genetic

In some plants, such as the soybean (Glycine max), fasciation is caused by a single recessive gene. This means that fasciation will only occur if both parents of a plant have that gene and pass it on.

Multiple distorted flowers Veronicastrum 'Fascination'

Multiple distorted flowers Veronicastrum ‘Fascination’

Physiological

Normal and Fasciated Spathyphyllum

Normal and Fasciated Spathyphyllum

In plants without the gene, fasciation is caused by disturbance to the meristem at the time of growth. This disturbance can be caused by

  • Mites or insects feeding on the shoot
  • Fungal, bacterial and viral diseases
  • A sudden change in temperature – eg going from low to high or high to low (especially in Hyacinthus)
  • Zinc deficiency or nitrogen excess
  • Drought followed by heavy watering

Frequently Fasciated Plants

The following plants have exhibited fasciation: soybean, many cacti, ferns, Euphorbia, Prunus, Salix, cannabis, Aloe, Acer, Forsythia, Delphinium, Digitalis, Taraxicum and Syringa.

Artificially Induced Fasciation

In some cases fasciation is seen as a desirable characteristic, it can lead to increased yield in crops due to the enlarged heads, or provide a talking point in ornamental displays. Examples are the maize, Celosia cristata and Asplenium cristata (note the species name ‘cristata’ – cristate is another word for fasciation). To this end, the above conditions can be induced or one of the following methods used:

  • Manipulating the photoperiod (exposure to light)
  • Using susceptible cultivars (see below)
  • Using radiation – gamma rays or ionizing x-rays.
  • Chemical application – growth regulators or polyploidzing agents
  • A cutting or scion taken from a fasciated plant will create a new fasciated plant

Veronicastrum ‘Fascination’ is a cultivar grown for its tendency to fasciate.

Fasciated stem of Veronicastrum 'Fascination'

Fasciated stem of Veronicastrum ‘Fascination’

Veroncastrum 'Fascination'

Veroncastrum ‘Fascination’

Fasciation in Cacti and Other Succulents

Many cacti and succulents are subject to fasciation, although the word more commonly used to describe this state is cristate. More than fifty cacti genera have shown cristation, as well as the succulent families Crassulaceae, Asclepiadaceae and Euphorbiaceae. Some cacti have ‘Cristata’ in the name. Fasciated cacti form ribbon like weaves, or have many divisions. Cristation is often cultivated in cacti, with cuttings used to perpetuate the cristate cacti. It is thought that some cacti species have a genetic propensity to cristation and somatic mutation (genetic alteration caused by environmental factors as described above) leads to the physical changes. Seeds from fasciated stems in cacti often lead to fasciated seedlings, although this is not necessarily true of other plants, Digitalis, when fasciated, does not produce fasciated seedlings.

Mammillaria elongata cristate

Mammillaria elongata cristate

Some more cacti showing signs of cristation

Fasciated Mammillaria compressa

Fasciated Mammillaria compressa

Normal and fasciated Mammilaria

Normal and fasciated Mammilaria

Euphorbia

Euphorbia

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 Fasciation in Ferns

Several ferns are especially cultivated to be cristate, such as Dryopteris affinis ‘Cristata’ or Asplenium cristata

Asplenium cristata

Asplenium cristata

 Additional information and pictures:

Plant Divisions: Flowering Plants

Leaf Variety in Magnoliophyta

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

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

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

Cronquist system

APG III System

APG III System

Key to Magnoliophyta plants

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

Anthurium and Ctenanthe – two flowering plants

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.

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: Cycads

Cycas

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

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

Unfurling leaves of Cycas rumphii

Trunk and roots

Trunk of Encephalartos ferox

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

Subterranean Stem of Cycas

Reproduction

Cones of Dioon and Ceratozamia

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

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

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

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 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

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

Ceratozamia with Female Cone

 Cycadaceae

Cycadaceae - Cycas seemannii

Cycadaceae – Cycas seemannii

Mature Female Cycas cone with seeds forming

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

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

Bowenia spectabilis