Identifying plants

A flora is a text written for the identification of flowering plant species. Some flora use only pictures to classify plants. More detailed texts use a more systematic approach where reference is made to a key of features that, by elimination, will lead to the name of a plant. Species are described in terms of their flowers, inflorescences, stems, leaves and fruit. This description will often include details of shape, size and colour of these plant parts.

Flowers. The number and arrangement of flower parts (see Figure 4.6) is the most important feature for classification and is a primary feature in plant identification. It can be described in shorthand using a floral formula or a floral diagram. For example, the flora formula, with the interpretation, for Wallflower (Cheiranthus cheiri), a member of the Cruciferae family is as follows:

symmetrical 4 sepals 4 petals in 6 anthers 2 ovaries joined flower in calyx corolla together

Cruciferae Cheiranthus Cheiri

Symmetrical Four Four Six Two ovaries flower sepals petals in anthers joined in calyx corolla together

Symmetrical Four Four Six Two ovaries flower sepals petals in anthers joined in calyx corolla together

Figure 4.6 Floral diagram of wallflower

Figure 4.7 Wallflowerflower (a) from above, (b) the side and (c) LS, illustrating the floral diagram above

Labiatae Ovary

Figure 4.7 Wallflowerflower (a) from above, (b) the side and (c) LS, illustrating the floral diagram above

Other examples of floral formulae include:

Sweet pea (Fabaceae):

Buttercup (Ranunculaceae):

Dead nettle (Labiatae):

Daisy

(Asteraceae):

Gl G

The way that flowers are arranged on the plant is also distinctive in different families, e.g. raceme, common in the Fabaceae; corymb and capitulum found in the Asteraceae and umbel, very much associated with Apiaceae (see Chapter 7 for more detail).

Leaf form (see Figure 4.8) is a useful indicator when attempting to identify a plant and descriptions often include specific terms, a few are described below but many more are used in flora.

Identfying Plants Leaf Descriptuion

Figure 4.8 Leaf forms: (a) linear e.g. Agapanths; (b) lanceolate e.g. Viburnum; (c) oval e.g. Garrya elliptica; (d) peltate e.g. nasturtium; (e) hastate e.g. Zantedeschia; (f) lobed e.g.

Geranium ; (g) palmate e.g. lupin; (h) pinnate e.g. rose

Figure 4.8 Leaf forms: (a) linear e.g. Agapanths; (b) lanceolate e.g. Viburnum; (c) oval e.g. Garrya elliptica; (d) peltate e.g. nasturtium; (e) hastate e.g. Zantedeschia; (f) lobed e.g.

Geranium ; (g) palmate e.g. lupin; (h) pinnate e.g. rose

  • Simple leaves have a continuous leafblade, for example: linear, lanceolate, ovate, obovate, orbicular, oval.
  • Margins of leaves can be described: entire, sinuous, serrate, and crenate.
  • Leaf vein arrangement also characterizes the plant: reticulate, parallel, pinnate and palmate.
  • Compound leaves, such as compound palmate and compound pinnate, have separate leaflets each with an individual base on one leaf stalk (see p117 for leaf structure), but only the axillary bud is at the base of the main leaf stalk.

Most horticulturists yearn for stability in the naming of plants. Changes in names confuse many people who do not have access to up-to-date literature. On the other hand, the reasons for change are justifiable. New scientific findings may have shown that a genus or species belongs in a different section of a plant family, and that a new name is the correct way of acknowledging this fact. Alternatively, a plant introduced from abroad, maybe many years ago, may have mistakenly been given the incorrect name, along with all the cultivars derived from it.

Evidence from biochemistry, microscopy and DNA analysis is proving increasingly important in adding to the more conventional plant structural evidence for plant naming. There may be differing views whether a genus or species should be 'split' into smaller units, or several species be 'lumped' into an existing species or genus, or left unchanged. It seems likely that changes in plant names will continue to be a fact of horticultural life.

There has been a massive increase in communication across the world, especially as a result of the Internet. The level of information about plant names has improved. The International Code of Botanical Nomenclature (ICBN) has laid down an international system. Within Britain, the Royal Horticultural Society (RHS) has an advisory panel to help resolve problems in this area. An invaluable reference document 'Index

Kewensis' is maintained by Kew Gardens listing the first publication of the name for each plant species not having specific horticultural importance. Cultivated species are listed in the 'RHS Plant Finder', which also indicates where they can be sourced, is updated annually and can be viewed on the Internet. Further cooperation across Europe has led to the compilation of The International Plant Names Index with associated working parties formed from scientific institutions and the horticultural industry.

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