Verticillus

Verticillus is a botanical term used to describe a whorl, or circular arrangement, of plant parts around a stem at a node. In its singular form, verticillus historically referred to a cluster of leaves, stipules, or floral parts that encircle the stem in a single level, giving a whorled appearance. In modern plant description, the same concept is more commonly expressed with terms such as verticillate or whorled.

In practice, plants described as having a verticillus display multiple organs at the same height around the stem. This contrasts with monochasial arrangements like opposite leaves (pairs at a node) or alternate arrangements (single leaf per node). When three or more leaves or floral elements radiate from a single point around the stem, the term verticillate is often applied.

The term also appears in discussions of inflorescences. Verticillate or verticillate-like inflorescences refer to groups of flowers arranged around the stem in a circular pattern, creating a ring or whorl of blossoms at a given level.

Etymology and usage have varied over time. Verticillus derives from Latin roots meaning a small whirl or turning, reflecting the circular arrangement described by the term. In contemporary botany, adopting verticillate or whorled is common, with verticillus retained mainly in historical or descriptive contexts.

See also: whorl, verticillate, phyllotaxy, inflorescence.