Definition - What does Pinnate mean?
In plant biology, a pinnate is a compound leaf structure with a feather-like formation of leaflets arranged either in pairs or alternating along the main stem. There are both odd and even pinnate leaflets.
Odd pinnate leaflets are those that are attached along an extension of the petiole called a rachis and have a terminal leaflet, hence, there is an odd number of leaflets.
Even pinnate leaflets are leaflets attached along the rachis that do not have a terminal leaflet, resulting in an even number of leaflets.
In a ‘twice pinnate’, the leaflets are also divided into additional leaflets, like in fern plants.
MaximumYield explains Pinnate
The term pinnate derives from the Latin word ‘pinna’, which means feather, wing, or fin. A pinnate is basically the arrangement of feather-like or multi-divided features arising from both sides of a common axis of a plant.
A concept similar to that of pinnate is ‘pectination’. A pectination is a comb-like arrangement of parts in plants arising from one side of an axis only.
The pinnation is commonly referred to in contrast to palmation. Palmation is the opposite of pinnation, in which the parts or structures radiate out from a common point.
Furthermore, the terms pinnation and pennation are related; although they are sometimes used distinctly, there is no consistent difference in the meaning or usage of the two words.
Trees having a leaf that is pinnately compound will have leaflets growing from several places along the stalk or rachis. Some trees have a leaf where at least some of the leaves are doubly compound (leaflets on a rachis and on a second rachis is called bipinnate) and the leaflets have mostly smooth margins.
An alternate botanical word for bipinnate is called pinnule. Pinnule or pinnula simply means a secondary division of a pinnate leaf.
In addition to plant biology, pinnation occurs in biological morphology in crystals, such as some forms of ice or metal crystals, and in patterns of erosion or stream beds.