Pinnately Compound Leaves

A pinnate leaf is any compound leaf where the leaflets attach along the petiole. This attachment gives the leaf a “feather-like” shape. They are commonly known as “feather-leaved”; the leaflets are referred to frequently as pinnae; and the phenomenon of pinnate arrangement is known as pinnation.

A pinnate leaf may end with an odd or even number of leaflets, in which the leaf may be referred to as odd pinnate or even pinnate. When it develops an odd number of leaflets, the odd leaflet is a terminal leaflet which is whorledly attached to the end of the petiole. If the number is even, the terminal leaflet is absent.

These leaflets are frequently depicted as oppositely attached. However, the leaflets may also be alternately attached; in this case, they are described as alternipinnate. Additionally, if the leaf is even pinnate and the leaflets are oppositely attached, the terminal leaflets will be whorled.

A bipinnate leaf is any twice compounded leaf rather than a single pinnately compound leaf. These compound divisions can occur multiple times within one compound leaf, with adjectives described for three (tripinnate) and four (tetrapinnate). A once pinnately divided leaf is also referred to as unipinnate.