Leaves long-lanceolate, base little differentiated to triangular or narrowly elliptic, shoulders absent, distal laminal margins plane or erect, apex broadly channeled or plane, acute, mucro very strong, of 6-10(-14) cells; costal adaxial stereid band smaller than the abaxial; distal laminal cells 8-10 µm wide. Sexual condition cladautoicous. Seta very short, less than 0.05 cm not including the vaginula. Capsule cleistocarpic, round, with a short-rostrate or conic, occasionally angled or curved apiculus.
As with Weissia ludoviciana, the gametophyte of W. muhlenbergiana is like that of W. brachycarpa, but differs to some extent in the distal leaf margins occasionally sharply inflexed. If the sporophyte has a hybrid origin, then the archegoniate parent has characteristics of both W. controversa and W. brachycarpa. The hybrid W. muehlenbergiana × W. controversa was reported by C. Williams (1966).