Stems: stout, ascending from a decumbent rooting perennial base. Leaves: pinnate, oblong, serrate. Flowers: few in an open cyme. Fruit: achenes glabrous, hairy receptacle becoming large and spongy.

This Purple Cinque foil is a marsh plant with a decumbent root and a somewhat woody base. The leaves are five to seven foliolate, the lower ones long-stalked and the upper ones nearly sessile, the leaflets being oblong, toothed, blunt at the apex and narrowed at the base. The showy flowers, which grow in an open cyme, have a large calyx which is dark purple within and much exceeds the small purple petals. The numerous stamens are inserted on the pubescent receptacle which becomes spongy in fruit.