A stipule is a small, usually paired appendage found at the base of a leaf, right where the leaf stalk meets the stem. Most stipules look like tiny flaps, scales, or leaf-like projections flanking the petiole, and they appear in an enormous range of flowering plants and even some ferns. Though easy to overlook, stipules serve real purposes and come in a surprising variety of forms, from the papery sheaths wrapping the stems of buckwheat relatives to the vicious thorns on an acacia branch.
Where Stipules Sit and What They Look Like
The classic stipule is a small, flat outgrowth at the very base of the petiole, one on each side. In many species they are green and leaf-like, though often much smaller than the leaf blade itself. In others they are thin and papery, brownish, or so reduced that you need a hand lens to spot them. Stipules typically appear in pairs because the leaf primordium produces one lateral expansion on each side of its base early in development. In some plant families, however, the two stipules fuse together or attach in unusual positions, which gives rise to several recognizable arrangements.
Not every leaf has stipules. Botanists describe leaves as “stipulate” when stipules are present and “exstipulate” when they are absent. Entire plant families tend to go one way or the other. Roses, peas, and members of the coffee family (Rubiaceae) nearly always have conspicuous stipules, while many families in the daisy or mint orders typically lack them. Whether a species has stipules, and what form they take, has long been used as a clue for identifying and classifying plants.
How Stipules Develop
Stipules originate very early in the life of a leaf. As a leaf primordium begins to push out from the shoot tip, two lateral bulges form at the base of what will become the petiole. These meristematic zones grow rapidly and differentiate before much of the rest of the leaf has taken shape. In the dogbane family (Apocynaceae), for instance, the structures that emerge from these stipular zones are among the first features visible on a young leaf primordium, already appearing by the second or third node.
Genetic studies in garden pea have clarified how stipule identity is established. A gene called COCHLEATA (COCH) acts as a master regulator: it is required for the initiation, growth, and full development of stipules. When COCH is knocked out, stipules fail to form properly. Interestingly, COCH also represses the genetic pathway that would otherwise push the stipule toward developing like a compound leaf blade. In wild-type peas, the result is a simple, rounded (peltate) stipule rather than a leaflet-like structure. A second gene called STIPULE-REDUCED (ST) works alongside COCH to shape the final form.1PubMed. Regulation of stipule development by COCHLEATA and STIPULE-REDUCED genes in pea Pisum sativum These findings reinforce the idea that the stipule is an autonomous lateral organ, not merely a bit of leftover leaf tissue. It has its own developmental program, comparable in complexity to the leaf blade itself.
Anatomy and Vascularization
Internally, stipules can range from simple sheets of undifferentiated tissue to highly organized structures with their own vascular supply. In many species, stipules receive veins that branch off from the lateral leaf traces running through the node. The family Cunoniaceae, which includes a number of Southern Hemisphere trees and shrubs, illustrates this well. Their characteristic interpetiolar stipules are fed by veins that originate from lateral leaf traces, sometimes supplemented by complete lateral traces of their own.2American Journal of Botany. Diverse Nodal Anatomy of the Cunoniaceae Having a dedicated vascular supply means these stipules can transport water and sugars, supporting photosynthesis or secretion.
In other species, stipules are non-vascularized and much simpler. The tiny secretory structures called colleters that form on stipules of the coffee and dogbane families, for example, are emergences without internal veins.3PubMed Central. Stipules in Apocynaceae: an ontogenetic perspective Whether a stipule is vascularized or not often correlates with its size and how long it persists on the plant. Large, persistent stipules that function like miniature leaves tend to have veins; small, quickly shed stipules often do not.
The Main Types
Stipules are grouped by where they sit relative to the leaf and stem and whether neighboring stipules fuse together. The most commonly recognized arrangements include:
- Lateral (free): One stipule on each side of the petiole base, not joined to each other or to anything else. This is the textbook form, seen in roses and many legumes.
- Adnate: The stipule is fused along part of its length to the petiole, so it looks like a wing or flange running up the leaf stalk. Common in roses of the genus Rosa, where the stipule appears to be part of the petiole itself.
- Interpetiolar: Stipules from two adjacent leaves on opposite sides of the stem fuse together, forming a single structure between the two petioles. This is a hallmark of the coffee family (Rubiaceae) and the Cunoniaceae.
- Intrapetiolar: The two stipules belonging to a single leaf fuse together on the inner (adaxial) side of the petiole, creating a scale or sheath that sits between the petiole and the stem.
- Ochreate (ocrea): The two stipules fuse into a tubular sheath that completely encircles the stem above the node. This is the defining feature of the buckwheat family (Polygonaceae). The ocrea’s shape, length, hairiness, and surface wax patterns vary enough among species to be taxonomically useful for telling apart closely related plants.4Phytotaxa. Systematic implications of ocrea morphology in the genus Persicaria (Polygonaceae), focusing on Türkiye
Some species also have structures called stipels, which are tiny stipule-like appendages at the base of individual leaflets within a compound leaf rather than at the base of the whole leaf. Stipels appear in certain legumes and a few other families and are thought to be developmentally related to stipules, though their anatomy is often simpler.
Functions of Stipules
The most widely cited role of stipules is bud protection. Young, developing leaves are vulnerable to drying out, fungal attack, and herbivory. Stipules physically cover and shield the bud, and in many species they produce sticky or waxy secretions that add a chemical layer of defense. In the dogbane and coffee families, stipules bear small glandular structures called colleters that release a mixture of mucilage, resins, and other compounds. Chemical analysis of these secretions has detected proteins, pectins, lipids, terpenoids, and tannins, among other substances.5South African Journal of Botany. Development, structure and secretion compounds of stipule colleters in Pentas lanceolata (Rubiaceae) This cocktail can deter insects and inhibit fungal growth, giving young organs a better chance of surviving to maturity.
Many stipules are also photosynthetic. In peas, the stipules are conspicuously large and green, and they contribute meaningfully to the plant’s carbon budget. Researchers studying winter pea found that stipules contain substantial amounts of chlorophyll a, chlorophyll b, and carotenoids, and that these pigment levels respond to foliar fertilizer treatments just as leaf blades do.6Agriculture and Forestry. Content and Ratio of Photosynthetic Pigments in Stipules of Winter Pea with Using Different Growing Technologies In species where the true leaf blades are reduced or modified into tendrils (as in some climbing peas), stipules can become the plant’s primary photosynthetic organs, effectively taking over the leaf’s job.
Beyond protection and photosynthesis, stipules serve other functions depending on the species. In some tropical trees, large stipules shade the stem surface and reduce water loss. In plants that interact with ants, hollow stipules can serve as nesting chambers (domatia), providing shelter for ant colonies that in turn defend the plant against herbivores. And as we will see below, stipules in some lineages have been evolutionarily co-opted into structures that look nothing like the small flaps they started as.
When Stipules Become Something Else
One of the more dramatic things about stipules is the range of structures they can turn into through evolutionary modification. The sharp, paired thorns at the base of acacia leaves are modified stipules. Unlike the thorns of a hawthorn, which are modified stems, acacia stipular spines are always found flanking the leaf base and are derived from stipular tissue. Several species of Euphorbia similarly bear stipular spines, and the classification of Euphorbia species has historically leaned on the form and arrangement of these spines to sort out relationships within the genus.
In other lineages, stipules have been modified into tendrils used for climbing. The greenbrier genus (Smilax) is a well-known example: paired tendrils sprout from the petiole base and coil around supports. These tendrils are stipular in origin, distinct from the leaf-blade tendrils found in peas or the stem tendrils of grapes.
Stipules can also become leaf-like and photosynthetically dominant, as mentioned in peas, or they can enlarge into bract-like structures that surround flower clusters. In some fig trees, the large conical caps that enclose developing buds are actually stipules. Once the bud opens, these caps fall away, leaving a conspicuous ring scar on the stem. If you have ever noticed a circular scar at each node of a magnolia twig, that too is the mark left by a deciduous stipule that did its protective job and dropped off.
Why Some Plants Have Lost Them
Given how useful stipules can be, it is worth asking why many plant lineages have abandoned them entirely. The answer likely comes down to cost-benefit trade-offs. Producing stipules takes resources: meristematic cells, vascular connections, and photosynthate. In environments or growth strategies where the leaf itself provides adequate bud protection, or where the plant invests heavily in other defenses like trichomes or chemical deterrents, the added expense of stipules may not pay off. Over evolutionary time, natural selection can reduce stipules to tiny vestiges or eliminate them altogether.
Some families show intermediate states. A species might produce stipules only on juvenile foliage and lose them on mature branches, or retain tiny stipular remnants that fall off within days of the leaf expanding. These patterns suggest that stipule loss is not always a clean, all-or-nothing event but can proceed gradually, with function eroding before the structure itself disappears.
Stipules in the Fossil Record
Stipules have a long evolutionary history, and recent fossil work has pushed their origins back further than previously recognized. The fern order Marattiales, which today includes large tropical ferns with fleshy stipule-like structures at the base of their fronds, turns out to have been stipulate since at least the late Paleozoic era. Fossils of an extinct group called Psaroniaceae, which are the stem-group relatives of living Marattiales, preserve paired, scaly, vascularized appendages at the base of their fronds in a position equivalent to where modern marattialean stipules sit. Researchers have reinterpreted these structures, previously called aphlebiae, as true stipules homologous to those of living Marattiaceae.7PubMed Central. Earliest evolution of stipules among vascular plants documented in the late Paleozoic stem group of Marattiales
This makes Marattiales the earliest plant group known to have developed stipules, predating the flowering plants by a wide margin. It also highlights an evolutionary pattern: the psaroniaceous stipules appear to have undergone a process of lamination, gradually becoming more leaf-like over time, a trajectory that converges with what we see in some flowering-plant stipules that take on blade-like functions.7PubMed Central. Earliest evolution of stipules among vascular plants documented in the late Paleozoic stem group of Marattiales The fact that ferns and flowering plants arrived at functionally similar stipules independently underscores how advantageous these structures can be in protecting developing organs.
How Botanists Use Stipules for Identification
For anyone trying to identify an unfamiliar plant, stipules are quietly one of the most useful features to check. Their presence or absence, their shape, and their position relative to the leaf and stem can narrow down a plant’s family quickly. If you see a tubular sheath encircling the stem at each node, you are almost certainly looking at a member of Polygonaceae. If pairs of stipules are fused between opposite leaves, you are likely dealing with a member of the coffee family. The paired thorns at the base of a leaf point toward certain legumes or Euphorbia species.
Even within a single genus, stipule characteristics can help separate species. In Persicaria (smartweeds and knotweeds), the length of the ocrea, the shape of its tip, whether it is hairy or smooth, and the texture of its surface wax differ enough to distinguish species that might otherwise look confusingly similar.4Phytotaxa. Systematic implications of ocrea morphology in the genus Persicaria (Polygonaceae), focusing on Türkiye This level of detail matters to field botanists and taxonomists, but it is also useful for gardeners and naturalists who want to tell apart the various weedy smartweeds growing in a ditch or garden bed.
Stipules You Encounter Without Realizing It
If you have ever grown peas or beans, you have seen stipules up close. The large, leaf-like structures at each node of a pea plant are its stipules, and in some cultivars they are nearly as large as the leaflets themselves. Rose growers routinely handle stipules as well: those winged flanges running along the base of each leaf stalk on a rose bush are adnate stipules, and they are one of the features that make rose foliage look distinct from other shrubs.
Rhubarb provides another everyday example. The large papery sheaths that wrap around emerging rhubarb stalks in spring are stipular in origin. They protect the developing leaves during the critical early growth phase and then dry up and fall away. Tulip tree (Liriodendron) buds are enclosed by conspicuous stipules that leave ring-shaped scars on the twig after they drop, a feature you can spot on bare winter branches.
Even rubber plants (Ficus elastica) grown as houseplants display prominent stipules. The pink or reddish sheaths covering each new leaf as it unfurls are stipules doing their protective job in real time. Once the leaf opens, the stipule drops to the floor, and most plant owners sweep it up without knowing what it was. Paying attention to these small structures adds a layer of understanding to ordinary gardening. The paired flanges, sheaths, spines, and tendrils at the base of leaves are all expressions of one ancient, versatile organ doing whatever the plant’s ecology demands.