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Pinna, a primary division with its leaflets of a bipinnate or tripinnate leaf.

Fronds two to six inches long, triangular-ovate, acute, broadest at the base, tripinnate.

From a systematic point of view these leaves indicate the origin of the water-parsnips from ordinary umbellifers, which generally have bi- and tripinnate leaves.

Pinnule, a secondary division of a bipinnate or tripinnate leaf, 66.

A more highly developed form of the typical plant, the lower pinnæ being often very broad, and the fronds tripinnate.