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 a premie ...

-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 Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

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

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is e ...

", or " fin". A similar concept is "pectination," which is a

comb A comb is a tool consisting of a shaft that holds a row of teeth for pulling through the hair to clean, untangle, or style it. Combs have been used since prehistoric times, having been discovered in very refined forms from settlements dating ba ...

-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 in different languages that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical ef ...

, 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; Published by Gerald Duckworth & Co. London, 4th ed 1928

Plants

Botanically Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...

, pinnation is an arrangement of discrete structures (such as leaflets,

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...

, 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

cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male o ...

s and grevilleas have pinnately divided leaves. Most species of

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

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 rachis. 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. Publisher: 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