Pinnation (also called pennation) is the arrangement of

feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and an exa ...

-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 Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

or metal crystals, and in patterns of

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

or stream beds. The term derives from the Latin word ''pinna'' meaning "feather", "

wing A wing is a type of fin that produces both Lift (force), lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform (aeronautics), planform. Wing efficiency is expressed as lift-to-d ...

", or " fin". A similar concept is "pectination", which is a comb-like arrangement of parts (arising from one side of an axis only). 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 In historical linguistics, cognates or lexical cognates are sets of words that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical effects on both the s ...

, and although they are sometimes used distinctly, there is no consistent difference in the meaning or usage of the two words.Jackson, Benjamin, Daydon; ''A Glossary of Botanic Terms with their Derivation and Accent''. Gerald Duckworth & Co. London, 4th ed 1928.

Plants

Botanically, pinnation is an arrangement of discrete structures (such as leaflets, veins, lobes, branches, or

appendages An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

) arising at multiple points along a common axis. For example, once-divided leaf blades having leaflets arranged on both sides of a

rachis In biology, a rachis (from the [], "backbone, spine") is a main axis or "shaft". In zoology and microbiology In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the ''rachi ...

are pinnately compound leaves. Many palms (notably the feather palms) and most cycads and grevilleas have pinnately divided leaves. Most species of

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

s have pinnate or more highly divided fronds, and in ferns, the leaflets or segments are typically referred to as "pinnae" (singular "pinna"). Plants with pinnate leaves are sometimes colloquially called "feather-leaved". Most of the following definitions are from Jackson's ''Glossary of Botanical Terms'':

Depth of divisions

* pinnatifid and pinnatipartite: leaves with pinnate lobes that are not discrete, remaining sufficiently connected to each other that they are not separate leaflets. * pinnatisect: cut all the way to the midrib or other axis, but with the bases of the pinnae not contracted to form discrete leaflets. * pinnate-pinnatifid: pinnate, with the pinnae being pinnatifid. Leaf morphology division pinnately-lobed.png, Leaf morphology division pinnately-cleft.png, Leaf morphology division pinnately-parted.png, Leaf morphology division pinnately-divided.png, Leaf morphology pinnatisect.png,

Number of divisions

* paripinnate: pinnately compound leaves in which leaflets are borne 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". Leaf morphology even pinnate.png, Leaf morphology odd pinnate.png, Leaf morphology alternipinnada.png,

Iteration of divisions

* 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

. Leaf morphology bipinnate.png, Leaf morphology type geminate-pinnate.png, Leaf morphology tripinnate.png, 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.Chittenden, Fred J. Ed., ''Royal Horticultural Society Dictionary of Gardening''. Oxford. 1951. Others also or alternatively apply it to second or third order divisions of a bipinnate or tripinnate leaf.Shastri, Varun. ''Dictionary of Botany''. Isha Books. 2005. . It is the ultimate free division (or leaflet) of a compound leaf, or a pinnate subdivision of a multipinnate leaf.

Animals

In animals, pinnation occurs in various organisms and structures, including: *Some muscles can be unipinnate or bipinnate muscles. *The fish '' Platax pinnatus'' is known as the pinnate spadefish or pinnate batfish.

Geomorphology

Pinnation occurs in certain waterway systems in which all major tributary streams enter the main channels by flowing in one direction at an oblique angle.

References

{{Reflist, 3 Plant morphology Leaves sv:Parflikig