Amentum

An amentum, commonly called a catkin in English, is a slender, unbranched inflorescence composed of many small flowers arranged along a central axis. Amenta are typically pendulous and wind-pollinated, and they often lack conspicuous petals, making the individual flowers inconspicuous to the casual observer. They occur in several groups of deciduous trees and shrubs, particularly those that rely on wind dispersal for pollen.

The flowers within an amentum are usually unisexual. Male catkins bear numerous stamens, while female catkins contain ovules and mature into fruits after pollination. In many species the male and female flowers are produced on separate plants (dioecious), though in other species both sexes may be found on the same plant (monoecious). The structure of the inflorescence and its timing support efficient wind pollination despite a lack of showy petals.

Ecology and phenology: Catkins often appear in late winter or early spring, sometimes before leaves emerge. Their pendant form can reduce interference from rain and aid pollen dispersal by wind. Pollination is typically wind-driven rather than insect-mediated, a characteristic shared by many unisexual, non-showy inflorescences.

Taxonomy and examples: The term amentum is used for catkin-like inflorescences in several plant groups, including Betulaceae (birches, alders, hazels), Salicaceae (willows, poplars), and related taxa. The etymology traces to Latin amentum, meaning a strap or thong, alluding to the slender, hanging form of the inflorescence.

See also: Catkin, Inflorescence, Wind pollination.