Stipule

In botany, a stipule is an outgrowth borne on either side (sometimes just one side) of the base of a leafstalk (the petiole). A pair of stipules is considered part of the anatomy of the leaf of a typical flowering plant, although in many species the stipules are inconspicuous or entirely absent (and the leaf is then termed exstipulate). In some older botanical writing, the term "stipule" was used more generally to refer to any small leaves or leaf-parts, notably prophylls.[1] The word stipule was coined by Linnaeus[2] from Latin stipula, straw, stalk.

Types of stipules

 
Glandular stipule of Euphorbia pteroneura

 
Stipular spines on the mesquite tree (Prosopis pallida)

 
Fused together and leaf-like stipules of Alchemilla mollis

 
Leafy stipules at the base of a Rose leaf (Rosa canina)

 
Stipules building glandular hairs on Jatropha spicata

 
Stipules protecting young leaves of Carpinus betulus (European Hornbeam)

 
Stipular spine clusters of Euphorbia spectabilis

 
Stipular spines accompanied by prickles of Euphorbia didiereoides

General characteristics

The position of stipules on a plant varies widely from species to species, though they are often located near the base of a leaf. Stipules are most common on dicotyledons, where they appear in pairs alongside each leaf. Some monocotyledon plants display stipule-like structures, but only display one per leaf. A relationship exists between the anatomy of the stem node and the presence or absence of stipules: most plants with trilacunar nodes have stipules; species with unilacunar nodes lack stipules.[3]

Stipules are morphologically variable and might appear as glands, scales, hairs, spines, or laminar (leaf-like) structures.

If a single stipule goes all the way around the stem, it is known as an ochrea.[4]

Types

According to duration

The three types of stipules according to duration are caducous, deciduous and persistent. Caducous stipules fall off before the leaf unfolds, while deciduous stipules fall off immediately after the leaf unfolds. Persistent stipules remain attached to the plant.[5]

According to shape, size and position

Stipules can be considered free lateral, adnate, interpetiolar, intrapetiolar, ochreate, foliaceous, bud scales, tendrillar or spiny.

A stipule can be fused to the stem, or to the other stipule from the same node.

A stipule is "adnate" if it's fused together on part of the petiole length, but the anterior is still free.

A stipule is "interpetiolar" if it is located in between the petioles, as opposed to being attached to the petioles, and generally one stipule from each leaf is fused together, so it appears that there's just one stipule between each leaf.[6]

A stipule is "intrapetiolar" if it is located in the angle that's between a stem and a petiole. In this case, the two stipules generally form together and appear to be one stipule.

A stipule is "ochreate" if a single stipule appears to be a solid tube that goes all the way around the stem.

A stipule is "foliaceous" if it is leaf-like. These are generally used to photosynthesize.

A stipule is considered a "bud scale" if it is hard or scaly and protects leaf buds as they form. These generally fall off as soon as the leaf unfolds.

A stipule is considered "tendrillar" if they are long thin tendrils, and are generally used by climbing plants.

A stipule is considered "spiny" if they are long and pointy. These are generally used to deter animals.

A stipule is considered to be "abaxial", "counter" or "leaf opposed" if it's located on the opposite side to where the leaf meets the stem.[4][7]

Purpose of stipules

Stipules have various functions. Some stipules are not well understood or may be vestigial.

It is known that foliaceous stipules are used like leaves to make energy for the plants. Sometimes stipules protect the next leaf or bud as it grows in then falls off after the leaf unfolds, as with Tulip Poplars.[4] Stipules can be used as climbing tendrils by climbing plants. Spiny stipules can be used to help protect the plant from animals.[8]

References
  1. Goebel, K.E.v. (1969) [1905]. Organography of plants, especially of the Archegoniatae and Spermaphyta. Part 2 Special organography. Translated by I.B. Balfour. New York: Hofner publishing company.
  2. Concise English Dictionary Wordsworth Editions Ltd. 1994, ISBN 1-85326-328-1
  3. Sinnott, E. W. & I. W. Bailey (1914). "Investigations on the phylogeny of the angiosperms. 3. Nodal anatomy and the morphology of stipules". American Journal of Botany. 1 (9): 441–453. doi:10.2307/2435043. JSTOR 2435043.
  4. Bell, Adrian D. (2008-01-01). Plant Form: An Illustrated Guide to Flowering Plant Morphology. Timber Press. pp. 74–79. ISBN 9780881928501.
  5. Darby, John (1860-01-01). Botany of the Southern States. A.S. Barnes & H.L. Burr. pp. 59-61. Caducous, Deciduous and Persistent stipules.
  6. Wyk, Braam Van; Wyk, Piet Van (2007-01-01). How to Identify Trees in Southern Africa. Struik. pp. 33–36. ISBN 9781770072404.
  7. "What are Stipules and what are its types ?". PublishYourArticles.net - Publish Your Articles Now. 2012-02-14. Retrieved 2017-04-04.
  8. Brown, Robert (1874-01-01). A Manual of Botany: Anatomical and Physiological for the Use of Students. Blackwood. pp. 149-152. stipule.

General references
  • Esau, K. 1953. Plant Anatomy. Second Edition. John Wiley & Sons, Inc., New York, London, Sidney. 767 pp.
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