Tag Archives: Plant

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

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.


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.


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 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 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.)


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.


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.


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.


  • 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

(For more information about the latest ICNCP, there’s an interesting article on Gardening Wizards, here)

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)



The Four Kingdom System

There are four kingdoms found in the Eukaryota Domain, they are Fungi, Plantae, Animalia and Protista. Plants and animals are familiar to most people, although there are specific criteria for each that may not be so familiar and a few very odd exceptions. Fungi were once included with plants, but are now known to be very different, and in some ways more similar to animals. Protista is a bit of a hodge podge as kingdoms go, it is unlikely to last much longer as one kingdom, and indeed many scientists have already rejected it because it doesn’t make much sense in evolutionary terms, however, the reordering is still in flux, so I will include Protista as one kingdom.

A clear to understand website about the Protista Kingdom and one from which I got the photo of Giardia lamblia below. http://www.uic.edu/classes/bios/bios104/mike/bacteria01.htm

A website that talks about a possible Seven Kingdom system http://www.fossilmuseum.net/Tree_of_Life/Domain_Eukaryota.htm




What makes an animal, an animal? Animals are heterotrophs, they cannot make their own food. They can move, are multicellular and reproduce sexually.

Evolutionary history: The earliest animal fossils that have been found are from sponges, dated 665mya, however, animals may have originated 1000mya. Most animals appeared around 542mya and relations of millipedes are the first animals proved to have made it on land 428mya.

Common examples: Crabs, coral, flies, birds and humans.010 (2)

Number of phyla and species: 35 phyla, this includes 13 phyla for different worm-like creatures. The most familiar phyla are:

  • Chordata  – contains mammals, but also fish and reptiles, about 60,000 species
  • Arthropoda  – thought to contain 80% of all living animal species, includes insects, spiders and crustaceans. About a million species have been named, but there are many times that number not yet discovered or classified.

In total it is believed there are between 3 and 30 million species of animal.

LizardHabitats: Polar to desert, temperate to tropical, oceans to mountains.


Animal Cell

Animal Cell

Cellular and structural description: Animal cells do not have cell walls or chloroplasts and are often a round shape. Animals contain tissues and organs of a complex nature, for example the tympanal organ for hearing in insects and brain tissue in humans.

Abilities and behaviour: Most animals move at some point in their life-cycle, they breathe out carbon dioxide and breathe in oxygen. They eat food for energy – fungi, plants, bacteria, other animals. Most reproduce using sperm and an egg, although some animals are hermaphrodite or reproduce asexually.

Some exceptional animals: Coral are colonies of genetically identical animals that don’t move. Sponges also don’t move and lack true tissues or organs. Green sea slugs use chloroplasts from algae they eat to then photosynthesize like plants. One species of hornet, Vespa orientalis, may derive energy from the sun. (For some other unusual animals see the Odds and Ends of Nature tab)



What makes a plant, a plant? Plants are autotrophs, producers, they make food (carbohydrate), by photosynthesis. Plants can’t usually move and their reaction to their environment is slow. They are multicellular and have complex organs and tissues.

Evolutionary history: Although plants originated in the sea, unlike animals and fungi, they did not evolve much there. Green algae (a primitive prototype plant and member of the Protist Kingdom) lived in the sea, but in order to make the move to land, where they could access more sunlight for photosynthesis, they needed to adapt to different, drier conditions. The first plant to grow on land was the now extinct Cooksonia (433-393mya), it had a waxy cuticle to stop the leaves drying out and roots to anchor it to the ground and absorb water. From Cooksonia evolved mosses, liverworts and hornworts (475mya), plants with a very basic ability to transport water. Ferns, followed by conifers and finally all flowering plants, evolved later.

SunflowerCommon examples: Sycamore tree, fern, sunflower, moss and box hedge.

Number of phyla and species: 10 divisions, 270,000 species.

  • 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

More on Divisions and plant evolutionary history in future blogs.

Habitats: Diverse, just about anywhere with air and sunlight.


Plant Cell

Plant Cell

Cellular and structural description: Plants cells have cell walls made of cellulose and chloroplasts. They have a very rudimentary circulatory system and the ability to sense their environment, but only simply – they can detect sunlight, but not see images, they can react to touch but it is mostly a slow process. They have organs and tissues, for example, the leaf is an organ and on its surface is photosynthetic tissue.

Abilities and behaviour: Plants are generally rooted in one place and do not move on their own, however they can grow in response to their environment. They give off oxygen and take in carbon dioxide through photosynthesis, a process which uses sunlight to make carbohydrate, which is then broken down by the plant for energy, however it is often consumed by fungi or animals instead. Plants reproduce sexually by fusing egg and sperm, but being unable to move they need different methods to transport the sperm to where the egg is, for example using wind or insects.

Some exceptional plants: Mimosa pudica can move, responding instantly to touch by collapsing its leaves against the stem, this is a defensive measure that hides the leaves from animals that might eat them. Ivy broom rape does not photosynthesize, but parasitizes ivy, growing from its roots in a similar manner to fungi. Some plants trap insects and digest them for nutrients, but not for energy in the way that animals do, these plants often move also, for example Venus Fly Trap. The Socratea exorrhiza is a tree described as being able to walk, but this is not walking in the way an animal would; it involves having above ground roots that move towards the sunlight by growing more roots on one side and allowing those on the shady side of the plant to die, so that in time the plant shifts both over- and underground.




What makes fungi, fungi? Fungi are heterotrophs, decomposers that cannot make food so they grow on living or dead organisms, breaking them down.

Evolutionary history: The first fungi were in the sea probably dating from 760-1060mya, fungi colonised the land long before animals or plants, probably 542-488mya.

Common examples: Athlete’s foot, coral spot (bright orange dots sometimes seen on leaves), white mushrooms, truffles, penicillin, bread mould.



Number of phyla and species: 6 phyla (although a seventh has been proposed). They are:

  • Chytridiomycota
  • Zygomycota
  • Ascomycota
  • Basidiomycota
  • Glomeromycota
  • Blastocladiomycota

10,000 species of fungus have been described, but there are thought to be at least a million. Fungi are more varied in the tropics than in areas closer to the North or South pole. For example in Britain and Ireland fungi outnumber plants 6:1, in Southeast Asia the ratio is 33:1.

Habitats: Fungi need plants, animals or other fungi to grow on or with. Most live on land, but a few live in water. Plenty live inside other organisms.


Fungal Cell

Fungal Cell

Cellular and structural description: Fungi have cell walls like plants, but made of chitin, the substance found in the hard exoskeletons of insects, rather than cellulose. The main part of a fungus is the mycelium, small threads that attach to other organisms to obtain food, these mycelium can grow for several km. Most fungi produce fruiting bodies these are what we think of as mushrooms, but are only a fraction of the actual fungus. Fungi have a simpler structure than plants or animals, but the fruiting body is an organ and it is made of tissue.

Abilities and behaviour: Fungi cannot photosynthesize and must consume food, they do this by attaching to other organisms (plants, animals or other fungi) by filaments and then take food from their host – sometimes this is a parasitic relationship, sometimes symbiotic (mutually beneficial, eg the fungi provides a means of extracting nutrients from the soil for its host plant) and sometimes saprophytic (consuming dead material, this is an essential part of the process whereby dead organisms break down, without these fungi the planet would be filled with dead bodies.)

Xanthoria Lichen

Xanthoria Lichen

Some exceptional fungi: Lichens are composite organisms, made up of fungi and algae working together. The alga can photosynthesize and so provides food for the fungus and the fungus protects the alga from desiccation in harsh environments. Lichens can grow in environments that neither algae or fungi could survive in alone. Along with bryophytes, lichens were probably some of the first organisms on land. Some lichens also contain Cyanobacteria (a bacteria).


Giardia lamblia

Giardia lamblia

What makes a protist, a protist? Essentially any organism that cannot be classified as a fungi, plant, animal, bacteria or archaea is classified as a protist, most protists are prototype fungi, plants and animals.

Evolutionary history: Algae were probably the first protists to appear, 1600-1700mya.

Common examples: Kelp, amoebas (Protozoa), seaweed, algae, the cause of malaria and sleeping sickness (NB: cyanobacteria are sometimes referred to as blue-green algae, but they are in the



Bacteria Domain), slime molds, diatoms (type of  algae). Volvox is a genus of single celled protists that live in colonies (see Odds and Ends of Nature tab for more about these and slime molds).

Number of phyla and species: 200,000 species. Usually ten phyla, although these often change.

Habitats: Protists live mostly in wet places, the sea, a damp corner, or an animal intestine.



Cellular and Structural description: Most are unicellular and invisibleto the naked eye. They are more complex than bacteria and have their nuclei wrapped in a membrane, but simpler than other eukaryotes having no specialised tissues, they do, however, have organelles in their cells such as mitochondria and chloroplasts.

Abilities and behaviour: Some protists are autotrophs, some are heterotrophs, some photosynthesize and expire oxygen, others consume and breathe in oxygen. The protists that move do so by a number of means such as pseudopodia or flagella.  Most Protists reproduce asexually, a few reproduce sexually and some alternate between the two.

Some exceptional protists: All protists are exceptions really.

Note: I recently received an email from someone helpfully pointing out that cells have only one Golgi apparatus, rather than the several that I had drawn. I have since altered these diagrams, sorry for the misinformation and thank you to the informer.