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Botanical Classification of Plants

This is the scientific method using the binomial nomenclature (two-name system) (see Biology and living things).

The seven main categories into which plants are grouped or classified are:

(i) Kingdom
(ii) Division
(iii) Class
(iv) Order
(v) Family
(vi) Genus
(vii) Species

Botanical classification and naming of plant begin, for all practical purposes, with placing the plant in its family. Most family names consist of one of the genera (singular-genus) plus the end, aceae (which means ‘belonging to, having the nature of), e.g. Ros-aceae(Roses).

There are a few exceptions with descriptive names e.g.

(i) Crucifera (i.e. cross bearers).
(ii) Gramineae (grasses).
(iii) Umbellifera (umbel bearers).

Most botanical names are in Latin. Examples:

(i)  Hedera (Ivy)
(ii) Lilium (Lily)
(iii) Pinus (Pine)

The name of the species consists of a generic name e.g. Solanum (Potato) followed by a specific adjective, e.g. tuberosum (tuber farming). The two words in combination form a specific name, Solanum tuberosum. This is enough to distinguish the species by name from the many thousands of other known species. This is the binomial nomenclature founded by Carolus Linnacus. For precision and to avoid confusion, the name of the author (initial only) is often indicated to show the classification systems used. (e.g. L. for Linnaeus) thus Solanum tuberosum L. The generic name of first name is started with a capital letter and underlined. The specific name (initial only) is placed at the end of the two names as shown above.

Descriptive epithets (adjectives) are sometimes used to distinguish or specify a name as shown in Box 1 below:

Box 1. Botanical epithets and their meanings



Box 2. Division of the vegetal world (plants)

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Box 3. The four divisions of the plant kingdom
(old methods of classification, still in use)
The four divisions of kingdom plantae are:

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In modern biology, vegetal (plants) are divided into three divisions as follows:

(i) Schizophytes: They are unicellular (one-celled), which means they consist of a single cell whose nucleus is not defined. These are the simplest and smallest living vegetables (of microscopic size). However, in spite of their simplicity, they are biologically very important because life on earth is due to these plants. Examples are bacteria which do not have chlorophyll, and blue-green algae or cyanophytes, which do have chlorophyll, e.g. Spiruline (Spirulina maxima).

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Blue-green algae, Spirulina maxima

(ii) Thallophytes: They have bodies called thalli (singular, thallus). These vegetables consist of multiple cells, which are all similar. There is no cellular differentiation (or rare) and so no organs or tissues. The thallus is formed by a mass of almost equal cells without vessels or conductive fibres and it lacks true roots, stems and leaves. Examples are algae, fungi and lichens such as Iceland moss (Cerraria lslandica).

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Lichens e.g Iceland moss (Cerraria Islandica)

(iii) Embryophytes: These plants consist of true roots, stems and different leaves, all of them crossed by conductive fibres and vessels. These plants possess differentiated cells, which form diverse tissues and organs. The embryo is the vegetative organ of these plants. All vegetables which are commonly called plants are embryophtes. There is a further division into:

C.1 Vascular crytogarns (no fibres)
C.2 Phanerogams (well differentiated organs and tissues)

– Vascular crytograms: All plants that have no flowers, but possess roots, stems and leaves crossed by vascular vessels, e.g., the horse tail Equisetum arrense and ferns.

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Fern polypodium vulgarel

Phonerogams: These plants with well differentiated organs and tissues (roots, stems and leaves) reproduce by means of seeds. They have flowers. This is their most remarkable feature, that is to say, visible well defined male and female reproductive organs. They are the most numerous plants on the planet (about 200,000 species). On the basis of the kind of seed, plants are classified into gymno-sperms (uncovered seeds) and angiosperms (covered seeds).

Gymnosperms have seeds that are not protected by fruits walls, i.e, they have uncovered seeds. E.g. coniferae such as pine tree and fir trees.

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(a) Pine (b) Silver fir

Angiosperms are plants which seeds are produced in a fruit wall, i.e. the seeds are contained within the ovary, which evolves into a fruit. These plants are the superior forms of vegetal rank and form the largest group of vegetables, e.g. Orange.

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Orange tree

Seed bearing plants may also be classified based on the number of seed cotyledons, i.e. mono-cotyledonous (one cotyledon) and dicotyledonous (two-cotyledon) plants. These may be differentiated as shown in Table 1.

Table 1. Differences between monocot and dicot plants

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    M.1 Single cotyledon – Maize
    M.2 Fibrous roots – Sugarcane, Buttercup
    M.3 Hypogeal germination – Maize
    M.4 Leave venation – Lily of the valley
    M.5 Scattered VB – Venila spp
    M.6 No secondary growth – Vanilla
    M.7 Flowers in threes, six, etc. – Grass
    M.8 No trees – Sugarcane

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       D.1   Two cotyledons – Castor seed
       D.2 Tap root system – Bean seed
       D.3 Epigeal germination – Castor
       D.4   Reticulate leaf venation – Syringa
       D.5 VB in a ring – Helianthus
       D.6 Secondary growth – Tillia
       D.7   Flowers in fours or fives – Gum plants