A leaf is made up of a long, extended blade called the lamina and a stalk-like petiole that connects it to the plant stem. Stipules are structures which resemble scales, spines or glands, and are typically found on either side of the leaf base in angiosperm leaves. The stipule of leaves are of several types. Let’s learn about them in detail here.
Table of Contents
Stipule – Meaning
Stipules are foliar appendages at the base of the leaf sheath or hypopodium that are often paired and sometimes leafy. They may range from quite leaf-like to small and inconspicuous structures.
They are typically regarded as a component of a normal flowering plant’s anatomy. Stipules, however, are not present in a lot of plants. The stipules’ shape and size also vary depending on the species. They typically take the form of scales, hairs, spines, glands, or leaf-like (laminar) structures. They nevertheless frequently appear in dicots. Stipule-like structures are also seen in monocots.
Types of Stipules
The nine major types of stipules are as follows:
- Free-lateral stipules
- Adnate stipules
- Interpetiolar stipules
- Intrapetiolar stipules
- Ochreate stipules
- Convoluted stipules (bud scales)
- Spinous stipules
- Tendrillar stipules
- Foliaceous stipules
Based on Position, Shape and Size
- Free lateral stipules – These are tiny free outgrowths that can be seen at the base of the petiole on both sides. Most members of the Malvaceae family have this feature. Example – China rose.
- Adnate stipules – In this case, the two stipules are connected to the petiole on both sides up to a certain distance, giving the impression that the base of the petiole is winged. Example – Rosa.
- Intrapetiolar stipules – Here stipules are present on opposing sides of the leaves and are joined by their inner margins. These stipules are positioned between the stem and the leaves. Most members of Rubiaceae have this feature. Example – Gardenia.
- Interpetiolar stipules – The stipules in question are tiny, semi-lanceolate entities that are found on both sides of opposite leaves. In this instance, two pairs of stipules from the two opposing leaves are joined by their outer margins. Example – Mussaenda.
- Foliaceous stipules – They are large leaf-like structures, such as those on foliaceous plants like Lathyrus aphaca. In Pisum sativum, this stipule looks like large leaflets.
- Ochreate stipules – These stipules, which enclose a larger section of the internode, are sheath-like and essentially tubular in structure. In this type, a number of stipules combine to form an enveloping sheath. It is a characteristic feature of the family Polygonaceae. Example – Polygonum.
- Bud scales or convoluted stipules – Convoluted stipules are stipules that have undergone modification to become membranous scale-like structures that surround and protect buds. Example – Ficus benghalensis.
- Spinous stipules – Consists of sharp spines, such as those on Acacia nilotica. They serve as defensive structures.
- Tendrillar stipules – When the stipules change into tendrils, such as in Smilax, it is called tendrillar stipules. These slender, tendril-like structures help the plants in climbing up.
Also Check:Leaves Morphology – Types and Modifications
Based on Duration
According to duration, there are three different types of stipules: caducous, persistent and deciduous.
- Deciduous stipules drop off right away once the leaf unfolds.
- Caducous stipules drop off before the leaf unfolds.
- Persistent stipules are affixed to the plant permanently.
Function of Stipule
Stipules serves various functions:
- They may protect the shoot apical meristem while the leaf is small and young.
- In other plants, they are large enough to contribute a significant amount of photosynthesis.
- They also help in the retention of moisture in some cases.
- Tendrillar stipules act as organs of support and spinous stipules act as organs of defence.
Keep exploring BYJU’S Biology to learn more such exciting topics.
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