page_title: Pinnation
section_title: Iteration of divisions
hierarchical_section_title: Pinnation / Plants / Iteration of divisions
caption_attribution_description: Caryota species in San Diego Zoo, showing strongly bipinnate leaves
context_page_description: Pinnation 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.
  The term derives from the Latin word pinna meaning "feather", "wing", or "fin". A similar concept is pectination, which is a comb-like arrangement of parts. Pinnation is commonly referred to in contrast to palmation, in which the parts or structures radiate out from a common point. 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.
context_section_description: 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.
  unipinnate: solitary compound leaf with a row of leaflets arranged along each side of a common rachis.
  The term pinnula (plural: pinnulae) is the Latin diminutive of pinna (plural: pinnae);  either as such or in the Anglicised form: pinnule, it is differently defined by various authorities. Some apply it to the leaflets of a pinna, especially the leaflets of bipinnate or tripinnate leaves. Others also or alternatively apply it to second or third order divisions of a bipinnate or tripinnate leaf.
  It is the ultimate free division (or leaflet) of a compound leaf, or a pinnate subdivision of a multipinnate leaf.
caption: Bipinnate leaves of species of palm in the genus Caryota
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