These are unusually large, deeply pinnatifid plants, known mostly from the southeastern Coastal Plain (F). This variant has not been generally recognized in recent treatments (e.g. FNA 2). It can be maintained in gardens (Cranfill 1980). Plants known as var. incisum (Howe) Robins. appear transitional to typical platyneuron; they extend up the Atlantic states to southern New England, and are reported inland to Ky. and W.Va. (F).