Botany for the Beginner

W.H. (Bill) Payne

The international system of classification of flowering plants, and hence for identification of plants throughout the world, is based upon the flower structure. The basic flower structure is quite simple involving very few botanical terms. All flowers appear to have developed along the pattern shown in the sketch below. Their purpose is to produce seed to maintain the species and this is achieved by fertilizing the ovules in an ovary which then mature to become seed. The various shapes and structures of flowers have developed over the ages to attract a pollinating agent, say a bird, bee or creatures from furry animals to tiny beetles.

Figure 1. Cross-section of a flower

The various parts of a flower usually surround the ovary with its style on top of it. The style receives pollen on its upper surface (the stigma) the whole female structure being known as the gynoecium or pistil. Pollen is produced at the ends of the male structure, the stamen, which comprises the stalk (filament) with anthers on top. Numerous stamens form a ring around the central style though some do not always fully develop and these are called staminodes. The pollen usually matures before the stigma on top of style is ready to receive it so that pollen from one flower is delivered to an older flower with a receptive stigma.

	Figure 2. Petalostylis flower
	Figure 3. Labichea flower

The rest of the flower exists to attract pollinators and position them such that pollen grains will adhere to their bodies and be deposited on a receptive stigma while they move from flower to flower in search of nectar provided by the flower.

The floral envelope could comprise a ring or whorl of petals (known as the corolla when fused in a tube), inside a whorl of sepals (known as the calyx), which may in turn be inside a whorl of bracts. The sepals may be coloured as well and the petals may not develop at all, the sepals being the showy part; the botanists have solved their dilemma by calling either or both the petals and calyx lobes, the perianth. The bracts cupping the flower are usually leaf-like and dull but can be the showy part of the flower. In some flowers they are deciduous.

The basic parts of the flower become specialized for each group of plants. For example:

• In the genus Petalostylis the flower has 5 petals (Fig. 2a). With the petals removed (Fig. 2b), we see the style on top of the hairy ovary is very enlarged to be boat-shaped or even petal like; it is three-lobed with the middle lobe terminated by a small stigma; there are three stamens with elongated anthers on tiny filaments and two staminoides.
  
  
• The flower of the related genus Labichea is similar but with 4 petals (Fig. 3a). The upper one usually has a red basal flare; the sepals behind the petals are not shown but the outer two are larger than the others; the outer floral envelope enclosing the flower in bud, the calyx, comprises five bracts. There are two stamens (Fig. 3b, petals removed) but the filaments (stalks) are short and the anthers on the end are enlarged, and for this species (see opposite) one is much larger than the other.

Take a little effort and find a whole new world of botany that is very simple.

From 'Australian Plants', the quarterly journal of the Association of Societies for Growing Australian Plants, December 1998.

Australian Plants online - 2006
Association of Societies for Growing Australian Plants