A recent collection of Platydictya minutissima from Kentucky, U.S.A., prompted a re-examination of the species. Based on rhizoid placement and pseudoparaphyllium form, the taxon is transferred to Serpoleskea as S. minutissima (Sull. & Lesq.) W.R.Buck & B.H.Allen. The species is restricted to eastern North America. Ecologically the taxon grows on moist rocks in or along streams, becoming submerged at times of high water.