Pinnation
Pinnate is a term used to describe feather-like or multi-divided features arising from both sides of a common axis in plant or animal structures, and comes from the Latin word pinna for "feather". A similar term is pectinate, which refers to a comb-like arrangement of parts (arising from one side of an axis). The term contrasts somewhat with palmate, in which the parts or structures radiate out from a common point.
Plants
Botanically, the term describes an arrangement of discrete structures (such as leaflets, veins, lobes, branches, or appendages) arising at multiple points along a common axis. For example, once-divided leaf blades having leaflets arranged on both sides of a rachis are pinnately compound leaves. Many palms (notably the feather palms) and most cycads and grevilleas have pinnately divided leaves. Most species of ferns have pinnate or more highly divided fronds, and ferns the leaflets are typically referred to as "pinnae" (singular "pinna"). Plants with pinnate leaves are sometimes colloquially called "feather-leaved".
pinnatifid and pinnatipartite – leaves with pinnate lobes that are not discrete, remaining sufficiently connected to each other that they are not separate leaflets.
paripinnate – pinnately-compound leaves in which leaflets are born in pairs along the rachis without a single terminal leaflet; also called "even-pinnate".
imparipinnate – pinnately-compound leaves in which there is a lone terminal leaflet rather than a terminal pair of leaflets; also called "odd-pinnate".
bipinnate – pinnately-compound leaves in which the leaflets are themselves pinnately-compound; also called "twice-pinnate".
tripinnate – pinnately-compound leaves in which the leaflets are themselves bipinnate; also called "thrice-pinnate".
tetrapinnate – pinnately-compound leaves in which the leaflets are themselves tripinnate.
Animals
In animals, pinnate is used to describe feather-like structures:
- Some muscles can be unipinnate or bipinnate muscles
- The fish, Platax pinnatus, is known as the pinnate spadefish or pinnate batfish.