Pinnation

Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis.

A similar concept is "pectination", which is a comb-like arrangement of parts (arising from one side of an axis only).

The terms "pinnation" and "pennation" are cognate, and although they are sometimes used distinctly, there is no consistent difference in the meaning or usage of the two words.

[5][6] Botanically, pinnation is 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.