enation

Enation is a term used in plant morphology to describe a small, leaf-like outgrowth on the surface of a plant, typically arising from the epidermis of leaves or stems. Enations are usually simple, flat or slightly raised projections and, in many fossil plants, lack vascular tissue such as xylem and phloem. Because of this absence of vasculature, enations are distinguished from true leaves, which contain vascular traces.

In paleobotany, enations are especially associated with early vascular plants, including certain lycopsids such as Lepidodendron. They contributed to the scaly or textured surface of branches in some Paleozoic plants. Enations are often discussed as potential precursors to true leaves (microphylls), illustrating a stage in the evolutionary transition from simple epidermal outgrowths to organized photosynthetic organs with vascular tissue.

The significance of enations varies across interpretations; some enations may be modified for other functions or may reflect developmental patterns that later gave rise to vascularized leaves. In living plants, the term is less frequently applied, with enations primarily appearing in discussions of fossil plant morphology and the evolution of leaf architecture. The distinction between enations and other epidermal outgrowths hinges on structural integration and the presence or absence of vascular tissue.

See also: leaf, microphyll, lycopsid.