Pinnate - Plants

Plants

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". Most of the following definitions are from Jackson's Glossary of Botanical Terms:

• 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.

• unipinnate: solitary compound leaf with a row of leaflets arranged along each side of a common rachis.

• The term pinnula is the Latin diminutive of pinna; 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 second or third order divisions of a bipinnate or tripinnate leaf.