Wednesday, April 20, 2011

Nature Word of the Week: Pinnate

This is the first posting of a new weekly feature... Nature Word of the Week.  Every Wednesday, I'll define a different nature-related word.  I'll try to mix it up, referencing different sources and choosing words of varying obscurity or technical level.  Probably nothing new for the professional scientist-types out there, but hopefully interesting or even instructive for casual nature observers like me.  I know I'll be learning as I create these posts.

So without further ado (OK, maybe just a little trumpet fanfare), the Nature of Portland proudly presents the very first, Nature Word of the Week!

This Week's Nature Word is: Pinnate


  1. Resembling a feather.
  2. (botany) Having two rows of branches, lobes, leaflets, or veins arranged on each side of a common axis

Pinnate leaves on a palm tree in the Phoenix genus - credit: Mmcknight4 via Wiktionary

Botanically, the term describes 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. Many palms (notably the feather palms) and most cycads and grevilleas have pinnately divided leaves. Most species of ferns 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".

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.
paripinnate: pinnately-compound leaves in which leaflets are born 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".
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.

A pinnate frond of the fern, Blechnum appendiculatum - credit: Marshman via Wikipedia
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