perfolation

Perfolation is a leaf morphology in botany in which the base of a leaf completely clasps or surrounds the stem, giving the appearance that the stem passes through the leaf. In perfoliate leaves the leaf tissue may encircle the stem to form a ring or cup, rather than simply attaching to the stem at a conventional petiole.

Perfoliate leaves occur in several plant groups and are most familiar in a few well-known species. Notable examples include Claytonia perfoliata, commonly known as miner’s lettuce, in which opposite leaves fuse around the stem, and Persicaria perfoliata, or mile-a-minute, a vine with perfoliate leaves that clasp the stem. The trait has evolved independently in different lineages and can vary in degree from a partial clasping to a nearly complete ring around the stem.

Development and morphology described as perfoliation result from the growth pattern of the leaf primordium, whose expansion encircles the stem and fuses with tissue on the opposite side. In some species the perfoliate condition is restricted to certain internodes or life stages, while in others it is persistent along much of the stem. The arrangement is visually striking and may interact with light capture, microhabitat around the stem, or herbivory, though the exact functional advantages are not universally established and may differ among species.

Etymology derives from Latin per- “through” and folium “leaf.” Perfoliation is discussed in botanical descriptions of leaf form and is contrasted with non-perfoliate, petiolate, or peltate leaves. Related concepts include perfoliate phyllotaxy and other leaf-stem integration patterns.