What are Stipules and what are its types ?

Leaves of some plants have lateral appendages on each side of leaf base, known as stipules. The leaves without stipules are known as exstipulate. Stipules are usually green, but sometimes appear withered also. Main function of these structures is to protect the leaf in the bud. When green these synthesize food also.

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A) According to duration, stipules may be of three types –

1. Caducous : Such stipules fall down before unfolding of lamina e.g., Michelia.

2. Deciduous : Such stipules fall down just after unfolding of lamina e.g., Cassia.

3. Persistent : Such stipules remain attached to the leaf for the whole life of the leaf e.g., rose, Hibiscus rosa-sinensis etc.

B) Stipules, according to their shape, size and location may be of the following types :

1. Free lateral stipules : These are two, small, green free stipules present on both lateral sides of the leaf base e.g., Hibiscus rosa sinensis  Gossypium, etc.

2. Adnate stipules : These are two lateral stipules attached to the petiole upto some distance but the anterior part remain free e.g., Rose (Fig. 7.4B) ground nut, Lupin etc.

3. Interpetiolar stipules : These stipules are also present on opposite or whorled leaves. In these leaves, stipule of each leaf remains attached with outer margin of another leaf of the same side. In this way these are alternate with leaves. In opposite leaves these are two in number e.g., Anthocephalus, Ixora Hamelia etc.

4. Intrapetiolar stipules : These stipules are also present on opposite leaves. In these, both stipules of each leaf join on inner margin and look like a single stipule. Thus these appear in the axil of leaf e.g., Gardenia.

5. Ochreate stipules : When both stipules of the leaf join on outer and inner margin and make a hollow tube which encircles (surrounds) the stem upto the upper part of node, the structure is known as ochreate stipule e.g., Polygonum Rumex etc.

6. Foliaceous stipules : These are two leafs by broad and green stipules. Due to the absence of axillary buds in their axil these can be distinguished from the leaves. In Lathyrus aphaca stipules are modified into leaves and leaves into tendrils. In Pisum sativum  foliaceous stipules are much developed and upper leaflets are modified into tendrils. Main function of these structures is to synthesize food.

7. Bud scales : These are scaly leaves which surround the leaf buds and protect them. They fall down after unfolding of the leaves e.g., Ficus, Artocarpus etc.

8. Tendrillar stipules : When stipules are thin and modified into wire like struc­ture, these are known as tendrillar. Tendrillar stipules help in climbing of plants. These are usually present in tendril climbing plants e.g.,Smilax.

9. Spiny stipules : When stipules are converted into sharp pointed structures, these are known as spiny stipules. These may be long (as in Mimosa and Acacia) or curved (in Ziziphus). They protect plants from wild animals .

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