Читать книгу British Wild Flowers: A photographic guide to every common species - Paul Sterry - Страница 12

BEING THE MAIN STRUCTURES responsible for photosynthesis, a plant’s leaves are its powerhouse. They vary from species to species and come in a wide range of shapes and sizes. Their appearance is an evolutionary response to the plant’s needs, in particular factors such as the habitat in which it grows, the degree of shading or exposure dictated by its favoured growing location, and rainfall. In most instances, all the leaves on a given plant are likely to be broadly similar to one another, although size tends to decrease up the stem of a plant. However, to complicate matters, basal leaves can be entirely different in appearance from stem leaves. This applies to a number of species, notably some umbellifers.

In essence, leaves are thin and rather delicate structures. However, rigidity is maintained by a network of veins through which pass the ingredients required for photosynthesis, and the products of the process.

The intricate network of veins in a leaf is often best appreciated after autumn leaf-fall in deciduous species. Softer tissue decomposes before the veins themselves disintegrate, leaving striking leaf skeletons.

Leaf shape is not an infallible guide to plant identity, so its importance as an identifying feature is secondary to the appearance of flowers. There are many instances where entirely unrelated plants have superficially very similar leaves and great care must be taken when using leaf shape alone for identification. However, there are also plenty of instances where leaf shape is distinctive and diagnostic, or where it allows the separation of closely related plants that have superficially similar flowers. So it is worth paying attention to the variety of leaf shapes found among British wild flowers, some of which are shown right and overleaf along with the common descriptive name by which their shapes are known. Also shown are a variety of distinctive marginal features.

OVATE

LANCEOLATE

ROUNDED

POINTED-TIPPED

SPOON-SHAPED

LINEAR

ROUNDED-TIPPED

TOOTHED (DENTATE) MARGIN

HEART-SHAPED (CORDATE) BASE

PINNATE

PALMATE

LOBED MARGIN

CLASPING BASE

TRIFOLIATE (OR TREFOIL)

FINELY DIVIDED