Oddpinnate

Oddpinnate, also called imparipinnate, describes a type of pinnate compound leaf in which the leaf is made up of an odd number of leaflets, including a single terminal leaflet. It is the opposite of paripinnate (even-pinnate) leaves, which have an even number of leaflets and no terminal leaflet. The term is used in botanical descriptions and identification keys to distinguish leaf architectures.

In odd-pinnate leaves, leaflets are arranged along a central rachis, with a terminal leaflet at the distal end. The number of leaflets is typically odd—common counts include 5, 7, or 9—though variation occurs among species. The rachis may bear stipules and can be winged or plain; leaflets may be sessile or have short petiolules. Margins vary widely, ranging from entire to serrate, and leaflets can differ in size along the rachis.

Taxonomic relevance: odd-pinnate leaves are widespread among angiosperms and are especially common in the Fabaceae and Oleaceae families. Notable examples include Robinia pseudoacacia (black locust) and many Fraxinus species (ash), which commonly have odd-pinnate leaves with several leaflets.

Identification tips: to determine odd-pinnation, count the leaflets on a mature leaf and look for a single terminal leaflet. If the leaflets number is odd and a terminal leaflet is present, the leaf is typically odd-pinnate. This characteristic helps in distinguishing leaf arrangements in field guides and taxonomic keys.