Mapping here is tentative. Although widely reported across eastern North America by some authors (e.g. K in progress), this taxon may have a largely southeastern range, and it appears particulalrly distinct on the Piedmont and Atlantic Coastal Plain (FNA 22, W). However, differentiation from typical triphyllum needs further research. Identification in the herbarium is often difficult. Treatment as subspecies may be preferred, although intergradation is unknown. In Ky. some populations of these rather small late-flowering plants appear to be associated with relatively damp and acid soils, especially in flatwoods and streamheads of the Mississippian and Appalachian Plateaus. A. pusillum differs from triphyllum sensu stricto as follows (W): leaves usually green beneath at maturity (versus glaucous); spathe flange 1-3 mm broad (versus 2-9 mm); spathe hood solid green or solid purple (versus green or green with purple stripes); sterile spadix ["appendix"] cylindrical (versus cylindrical to clavate); plants mostly up to 2 dm tall or rarely to 4 dm (versus often up to 4 dm or rarely to 9 dm); 2n = 28 (versus 56).