Plant Classification
Family
A botanist called Carl Linnaeus devised a scientific way of naming plants in the 18th century. This method is still used today. Botanical names are written in Latin and are understood by horticulturalists throughout the world. Plants with common ancestry are given a name called a family name. A family usually contains a significant number of genera. Plants in the same family often look entirely different so the horticulturalist is often surprised to learn that two entirely distinct plants evolved in this way. For instance, the family Rosaceae contains the genera Prunus and Rosa, yet plants from each of these genera tend to look entirely different. This tells us that the Rosa ‘Crimson Shower’ is in the same family as Prunus lusitanica and this is quite surprising. Rosa ‘Crimson Shower’ has large red flowers and few leaves. In contract Prunus lusitanica has small white flowers and numerous large leaves.
Genus
Individual plants are given a first name and this is called the ‘genus’. Plants of the same genus will have a common ancestry, hence they share many characteristics. The genus always is Latin and always begins with a capital letter. An example of a genus is Hebe. Hebes vary considerably in appearance. For example the Hebe armstrongii looks considerably different to the Hebe ‘Autumn Glory’. However, these two Hebes are similar because they are both compact bushes. As we can see plants of the same genus are similar but still entirely distinct.
Species
A plant is given a second name called the species. Plants of the same species share similar characteristics, as they have a common ancestry. Plants of the same species are able to breed amongst themselves. The species name is in Latin and it is descriptive of the plant. The species name may tell us the colour of the plant as in Digitalis purpurea (foxglove). Purpurea is Latin for purple and foxgloves are in the Digitalis genus. In the same way the name of the species may inform us about the plants habitat. For example, Fagus sylvatica (Beach Tree) tells us where the plant likes to grow because sylvatica means ‘forest loving’. Species may also be named after the country of origin as in Mahonia japonica, which is unsurprisingly from Japan. Species can also be named after their growth habit as in Rubus fruticosus (bramble). Fruticosus means bushy in Latin and reflects the growing habit of Rubus fruticosus. In addition species can be named after the discoverer of the plant in question. For example, Darwin discovered Berberis darwinii (barberry) so the species name of this plant is darwinii.
Varieties
Plants can have many varieties. Varieties can be formed naturally or through selective breeding. Varieties that are formed through selective breeding are called cultivars. An example of a variety that occurs naturally is Fagus sylvatica purpurea.
Cultivars
Cultivars are produced by selective breeding. Cultivars are created by horticulturalists and botanists to ‘improve’ the characteristics of plants. Many ornamental plants are cultivars that are breed to improve the form and colour of their flowers. Philadelphis coronarius 'Aureus’ is a cultivar which has attractive bright, golden leaves that turn soft greenish gold towards the end of the summer. Plants are selectively breed to increase yield, improve flavour, resist disease, increase vigour and so on. The cultivar name is chosen by the breeder, hence this name is in the breeders own language. The cultivar name comes after the species name and it is always in inverted commas. The cultivar name often refers to the name of the breeder. For example there is a plant called Verbena ‘Lawrence Johnston’. This is named after the famous garden designer and plantsman Lawrence Johnston. The cultivar may also refer to the way the plant appears. For instance, Leucospermum ‘Scarlet Ribbon’ appropriately has a red and delicate flower.
Hybrids
Hybrids are formed when two plants of different varieties, species or genera reproduce. This can occur naturally or as a result of selective breeding. They sometimes have highly desirable qualities. Horticulturalists and botanists produce hybrids to ‘improve’ the quality of plants. Hybrids may look more attractive or produce better or more seeds and so on. Hybrid rice has dramatically increased rice yields in China because it grows vigorously. When two plants of different species reproduce they create a hybrid called a interspecific hybrid. Tilia x europeae is an example of an interspecific hybrid. We know this because a ‘x’ is positioned between the names. When plants of different genera cross-pollinate the resultant hybrid is called a bi-generic hybrid. These hybrids have a ‘x’ placed in front of the genus name. An example of a bi-generic hybrid is x Osmaria burkwoodii.
Kingdom
All plants belong to the Plantae family. This excludes Fungi and Bacteria (prkaryotae) and Protoctista (all other organisms). Plants are divided into classes. Flowering plants are called Angiosperms whilst non-flowering plants are called gymnosperms. Angiosperms and divided into dicotyledons and monocotyledons. Dicotyledons have two cotyledons in their seeds. They have net-like veins and they have four or five petals or multiples of four or five petals. Monocotyledons, in contrast, have one cotyledon in their seed. The veins in their leaves are parallel to each other. Their petals are in threes or multiples of three.
Identifying Plants
Looking closely at the leaves, flowers, stems, buds and seeds of plants enables us to identify them. In other words, we should identify plants by looking, smelling and touching them so that we are aware of their morphological and botanical features. Leaves have many features that can help us to identify them. For instance, a Ilex aquifolium can be identified from its thick, glossy, spiny leaves. Below are some key leaf features to look for when identifying a plant.
The Leaf Shape
Leaf shapes can help us to identify plants. For example, the leaves of a Pinus nigra are long, thin and needle-like. In contrast the leaves of a Corylus avellana are serrated, rounded and comparatively large.
Leaf veins
Close inspection allows us to observe the veins within leaves. The leaves of a Bambusa vulgaris have veins that run in parallel stripes along the length of the leaf. In contract the veins of an Acer pseudoplatanus are net-like.
Compound leaves
When separate leaflets are based on one leaf stalk they are called compound leaves. These leaves can be identified by the fact that only one axillary bud is at the base of the main stalk. Fraxinus excelsior have compound leaves.
Stems
Stems are sometimes rough and sometimes smooth. Feeling stems can therefore give us clues as to the identity of the plant. Taking note of the colour of the stem also helps us to identify the plant. For example, Acer pseudoplatanus have stems that are smooth when the plant is young. When the plants mature they have wrinkled stems. Betula pendula stems have white spots when young. The mature stems, on the other hand, are predominantly white. The stems of Corylus avellana have fine red hairs. Thus, feeling and looking closely at stems helps us to identify plants.
Flowers
Flowers are very distinctive and play a vital role in the identification of plants. Flowers are arranged in similar ways on plants of the same kind. The horticulturalist should take note of the number of anthers, sepals, petals and ovaries. In horticulture books flowers are often illustrated and described in detail, facilitating the process of identification for the horticulturalist. A Cheiranthus cheiri has 4 sepals, 4 petals, 6 anthers and 2 ovaries joined together. Noting these botanical features helps us to identify the plant in question.
Seeds
Plant seeds can help us to identify plants. For example a Pinus nigra will produce cones that are ovoid and pale brown when fully grown. Fraxinus excelsoir produce notable clusters of winged fruits, whilst Taxus baccata produce distinctive, fleshy red fruits.
Keys can be used to identify plants
Identification keys can be used to deduce the identity of a plant by a process of elimination. Questions are asked relating to flowers, stems, leaves, fruit and so on. For example an identification key may ask: Are the leaves lobed or not? Once all the questions on the identification key are answered the name of the plant the horticulturalist is referring to will hopefully be revealed. There are many plant identification keys around for instance the Natural History Museum website has a ‘Tree Identification key’ alongside others. It is a good idea for the horticulturalist to check that she has identified the plant in question correctly. As John E . Preece and Paul E. Read write in The Biology of Horticulture: An Introductory Textbook:
“once a student identifies a plant … he or she should seek corroboration by comparing the plant in hand with a published description or by consulting one or more additional sources.”
(John E. Preece and Paul E. Read, The Biology of Horticulture: An Introductory Textbook, 1993, Page 20)
Developments
Plants are sometimes reclassified if new information about their origin comes to light. Developments in the science of botany sometimes make reclassification of plants appropriate. The renaming of plants can inconvenience the horticulturalist but it is surely sometimes a necessary measure because the names are supposed to be organised scientifically so that they reflect the evolution of plants.
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