Imparipinnate

Imparipinnate is a botanical term used to describe a type of pinnately compound leaf in which the number of leaflets is odd. The defining feature is a single terminal leaflet at the tip of the rachis, resulting in an odd count of leaflets along the rachis. The leaflets are typically attached to the central axis (the rachis) by small stalks called petiolules and are arranged along the rachis in an alternating or near-opposite pattern.

In contrast, paripinnate (even-pinnate) leaves have an even number of leaflets and lack a terminal leaflet, producing no single terminal leaflet at the end of the rachis. A related arrangement is bipinnate, where leaflets are subdivided further into smaller pinnules on secondary pinnae. Imparipinnate leaves are described for species across a range of dicotyledonous plants, and the pattern is often noted in field and herbarium descriptions to aid identification.

Morphologically, the number of leaflets in imparipinnate leaves can vary from a few to many, and leaflet size, shape, and margin can differ among species. The terminal leaflet may be particularly prominent, reduced, or occasionally absent in some individuals or forms, but the typical pattern is the presence of a single terminal leaflet.

The term imparipinnate is used in plant descriptions, floras, and keys to distinguish leaf architecture. It derives from Latin impar, meaning not even, and pinnatus (or pinna), meaning feather or wing, reflecting an odd arrangement along the rachis. See also paripinnate and bipinnate.