Sterile colonies of P. incurvum can be very reminiscent of Weissia controversa , but the Ptychomitrium plants are more glossy and their leaves have smooth cells and lack the strongly involute margins of Weissia . Grimmia drummondii W. M. Wilson, J. Bot. Plants dull, small, cespitose, yellowish to dark green. Stems erect, to 0.5 cm tall. Calyptra lobes one third to one half length of calyptra.
Sporophytes are very frequent and abundant.
In urban areas in the southeastern United States P. drummondii is often frequent and abundant on trees in parks and campuses and along city streets. Chromosome studies on some mosses of the southeastern United States. Anderson, L. E., H. A. Crum and W. R. Buck. List of the mosses of North America north of Mexico. Buck, W. R. 1979.