Stipules in Leaf – Definition, 9 Types of Stipules & Function
STIPULES DEFINITION: A stipule is the outgrowth of the hypopodium or leaf base. Ordinarily a stipule is a tiny structure growing on both sides of a leaf at its base, but in many cases they are large and conspicuous or variously modified to discharge special functions.
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TYPES OF STIPULES
There are several types of stipules, viz :- i) free-lateral, (ii) adnate, (iii) intrapetiolar, (iv) interpetiolar, (v) ochreate, (vi) foliaceous, (vii) tendrillar, (viii) spinous and (ix) bud scales.
(i) Free-lateral – These are tiny slender free outgrowths on both sides of the petiole at the base. This type is found in most members of the family Malvaceae, e.g. Hibiscus rosa-sinensis (China rose), Abelmoschus esculentus.
(ii) Adnate – Here the two stipules are attached with the petiole on both sides upto certain distance so that petiole-base appears to be winged, e.g. Rosa sp. (Rosaceae).
(ii) Intrapetiolar stipules – When stipules, occurring on both sides of opposite leaves, unite together by their inner margins and are placed in between the leaves and stem i.e. at the axils of a leaf e.g. Gardenia jasminoides (Rubiaceae). This type is characteristic of the family Rubiaceae.
(iv) Interpetiolar stipules — These are present in most of the plants of the family Rubiaceae e.g. Ixora (Rangan), Anthocephalus indicus (Kadam) etc. These stipules are small, semi-lanceolate bodies occurring on both sides of opposite leaves, here two pairs of stipules of the two opposite leaves unite together by their outer margins — as a result the four stipules are transformed into two fused stipules and appear on two sides of the stem between the petioles of the two opposite leaves.
(v) Ochreate stipules – Ochreate stipules are sheath-like and more or less tubular in structure, enclosing greater portion of the internode. In this type several stipules unite together to form the enveloping sheath.
These stipules are the characteristic feature of the family Polygonaceae, e.g. Polygonum barbatum (Pani marich), Rumex vesicarius (Chuka palang) etc.
MODIFIED STIPULE
(vi) Foliaceous – Foliaceous stipules are very conspicuous and large leaf-like on the both sides at the leaf base. In Pisum sativum (Papilionaceae), the foliaceous stipules look like large leaflets. In Lathyrus aphaca (Jangli matar, Papilionaceae), the entire leaf is modified into tendril, the large foliaceous semi-triangular stipules do the function of leaves.
(vii) Tendrillar — In this type the stipules become modified into coily and slender tendrils which help the plants in climbing up. Tendrillar stipules are found in Smilax zeylanica (Liliaceae).
(viii) Spinous stipules are those which are modified to form spinous structures, e.g. in Capparis spinosa (Capparidaceae), Zizyphus mauritiana (Rhamnaceae), Acacia sp. (Mimosaceae) etc. the stipules are modified into sharp pointed structures. These spines serve as defensive functions.
(ix) Convolute or Bud-scales – When stipules are modified into membranous scale-like structures and protect buds by covering all round, e.g., Artocarpus heterophyllus, Ficus benghalensis (Moraceae) etc. Function is protection of buds.
Plant Stem – Types, Functions & Modification of stem with Examples
Types of Venation – Difference Between Parallel and Reticulate Venation
FUNCTION OF STIPULES
The functions of stipules are various; these are, (a) protection of leaf bud, (b) retention of moisture in some cases, (c) function of leaves e.g. as by foliaceous stipule, (d) as defensive organs by spinous stipules, (e) as organs of support by tendrillar stipules.
Stipel — These are two small stipule-like appendages, present at the base of a leaflet in some compound leaves. Stipels are seen in many genera belonging to the family Leguminosae e.g. Dolichos lablab, Vicea faba, Desmodium sp. etc.
