atrichous

Atrichous is an adjective used in biology to describe organisms or surfaces that lack hairlike projections. The term derives from the Greek a- meaning without and trichos meaning hair. It is used across disciplines to denote the absence of different kinds of hairlike structures, including cilia, flagella, or plant trichomes.

In bacteriology, atrichous commonly refers to bacteria that lack flagella. Such cells are typically non-motile or less motile, in contrast to motile forms that bear flagella in various arrangements (for example, monotrichous or peritrichous). The designation helps distinguish strains in motility tests and can reflect genetic or environmental factors that influence the presence of flagella.

In botany and plant sciences, atrichous describes plant surfaces or structures that lack trichomes, the tiny hairlike outgrowths on leaves, stems, or other organs. Glabrous leaves or fruits are described as atrichous. The absence of trichomes can affect texture, water retention, and interactions with herbivores and environmental factors.

In other contexts, atrichous may refer to the absence of cilia on cells or organisms, for example in certain protozoa or epithelial cells. As with other uses, the term is general: it denotes the absence of a particular hairlike structure and is often clarified by specifying which structure is missing (flagellum, cilium, or trichome).