Pinnation
（重定向自Tripinnate）
![A simple pinnate (unipinnate) frond of the fern, Blechnum appendiculatum.](/Images/godic/202502/17/Fern_frond_pinnate2425.jpg")
![Bipinnate leaves of species of palm in the genus Caryota](/Images/godic/202502/17/Caryota_bipinnate_leaves_IMG_53852425.JPG")
Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in patterns of erosion or stream beds.