sessile

Sessile (from Latin sessilis, "sitting") is an adjective used in biology and related fields to describe an organism or structure that is attached directly by its base, lacking a stalk or means of self-propelled movement. In everyday use, sessile is contrasted with motile, meaning capable of movement from place to place.

In zoology and ecology, sessile organisms are anchored to a substrate for all or most of their life cycle and do not actively move about. Examples include adult barnacles, corals, sponges, and many bryozoans. Some organisms may disperse as larvae and then become sessile as adults. Some algae and plants also have sessile forms, particularly when attached to rocks or other substrates.

In botany, sessile describes plant organs that lack a stalk; a sessile leaf attaches directly to the stem, while a leaf with a stalk is called petiolate. A sessile flower or fruit is attached directly to the plant without a pedicel or other stalk.

In medicine, sessile describes a growth with a broad base attached to mucosa or tissue, such as a sessile polyp, in contrast to pedunculated growths that are stalked.

In materials science, the term sessile drop denotes a liquid droplet resting on a surface, used in contact angle measurements to assess surface energy and wettability.