Perfoliation

Perfoliation is a plant leaf morphology in which the leaf blade closely surrounds the stem, giving the appearance that the stem passes through the leaf. In complete perfoliation the stem is almost entirely enclosed by the leaf margin; in partial perfoliation, the leaf base wraps around the stem for only part of its circumference. Perfoliate structures may involve the leaf blade embracing the stem or, in some cases, the petiole surrounding the stem before attaching to the blade. Perfoliate leaves are distinct from peltate leaves, where the petiole attaches to the blade away from the margin, and from sessile leaves that lack a distinct stalk but do not enclose the stem.

Perfoliation occurs in a relatively small number of angiosperm lineages and has been observed in both herbaceous and woody plants, including some annuals and climbers. It arises through developmental changes in leaf growth, often via fusion of the leaf base around the stem or by leaf blades that grow to surround the young shoot. The adaptive value of perfoliate leaves varies by species, and in many cases it is viewed as a neutral or variation rather than an obligate adaptation; hypotheses regarding function include protection of growing points, optimization of light capture, or deterrence of herbivory, but no universal explanation applies.

Terminology: The term perfolation comes from Latin perfolatus, meaning through-leaf. In botanical descriptions, a leaf or leaf base described as perfoliate is one that completely or almost completely encloses the stem. Perfoliation highlights the diversity of leaf morphology and its occasional occurrence across different plant groups.