On the basis of origin and function, leaves are of he following kinds:
Types of leaves
1. Cotyledonary Leaves
These are the embryonic leaves of seed. Usually these contain reserve foods, due to which these become fleshy e.g., beans and gram. In other plants as Ricinus. these are thin and flat. In Geranium mole these are lobed. In monocot plants there is one cotyledon, called scutellum and in dicot plants are present two cotyledons.
2. Bract leaves or hypsophylls
Bracts are the leaves which contain flower or inflorescence in their axil. These are usually small and green but in some plants as Bougainvillea (Fig. 7.IB) and Euphorbia; these are large and bright coloured. Usually their function is the protection of flower buds from sun and rain. Coloured bracts also attract insects for pollination.
3. Scale leaves or cataphylls
These are usually present on underground stems (e.g., rhizome) and are usually brown or grey coloured membranous structures. Actually, scales are small, sessile, chlorophylless leaves. Buds are present in their axil. Scale leaves are usually dry and act as a protective covering for buds e.g., ginger but in onion and garlic (underground bulb), scale leaves store food and become fleshy.
First few leaves on a stem, different from other leaves.
5. Floral leaves or sporophylls
Sepals, petals, androecium and gynoecium all are modified leaves. These are known as floral leaves or sporophylls. Sepals are green and flat like a leaf. Petals are also leaf like, but the colour of petals is not green. Both of these protect the reproductive organs (androecium and gynoecium). Corolla, being coloured, attract insects for pollination. Androecium and gynoecium take part in reproduction.
6. Foliage leaves :
Normal leaves attached on aerial stem and branches are called foliage leaves. These are usually green coloured. These are flat. Main function of these leaves is to take part in photosynthesis, respiration and transpiration- The word ‘leaf is normally used for the foliage leaves.