unipinnate

Unipinnate is a botanical term used to describe a type of pinnate compound leaf in which the leaf blade is divided into multiple leaflets arranged along a single central axis, the rachis. The leaflets are typically attached to the rachis by short stalks called petiolules, though some may be sessile. The arrangement gives the appearance of a single feather-like line of leaflets extending from the base of the leaf stalk.

In unipinnate leaves there is no subdivision of the rachis into additional branches that would form secondary rachises (pinnae). By contrast, bipinnate leaves have leaflets arranged on secondary axes (pinnae) that themselves arise from a main rachis. Unipinnate leaves can be described as paripinnate or imparipinnate, depending on whether a terminal leaflet is present at the tip of the rachis.

Common examples of plants with unipinnate leaves include several species of the Fabaceae, such as Robinia pseudoacacia (black locust), and Juglans species (walnuts). These leaves typically feature many leaflets along a single rachis, producing a feather-like profile.

The term unipinnate is derived from Latin roots meaning “one” (uni) and “feather-like” (pinnatus), reflecting the feathered arrangement of leaflets along one axis. It is primarily a descriptive term in morphology and is used to distinguish leaf architecture within the broader category of pinnate (feather-like) leaves.