Pinnate

Pinnate (from the Latin pinna, "a feather"), a term applied to compound leaves when the leaflets (pinnce) are arranged along the sides of a mid-rib or rachis. If there is an odd leaflet terminating the rachis, as in the rose or the elder, the leaf is imparipinnate or unequally pinnate; if not, as in Acacia, it is paripinnate, equally or abruptly pinnate. If the pairs of leaflets (juga) are alternately large and small, as in the potato, the leaf is interruptedly pinnate, as is also the leaf of Acjrimonia, which, having a larger terminal leaflet, is also termed lyrately pinnate. When some or all of the divisions of a pinnate leaf, still termed pinnce, are themselves pinnate, so that the primary rachis bears seconda-ry rachides, the leaf is bipinnate; or if again divided, as in many ferns, tri-pinnate. The ultimate leaflets are called pinnules. A simple leaf lobed in a similar manner may be pinnatifid, pinnatipartite, or pinnatisect, according to the depth of the lobings.