Ephemerum spinulosum Bruch & Schimp. ex Schimp., Syn. Musc. Eur., ed. 1, 1: 6. 1860.
Protologue: U.S.A. Ph. serratum β angustifolium H. et W. in Drum. Musci amer. II. [ Louisiana, without locality, Drummond, Musci Americani (Southern States) No. 2 (NY, DUKE)].
Plants pale green, with abundant protonemata. Leaves to 1.4 mm long x 0.4 mm wide, linear-lanceolate, acuminate; margins spinose-dentate; costae more or less percurrent, sometimes lacking in the lower parts of the leaves, dorsally roughened; upper leaf cells oblong-rhomboidal, 4-6:1, scindulose to almost smooth. Rhizautoicous or dioicous. Capsules ovoid, obliquely apiculate, 0.5–0.6 mm long. Spores bluntly papillose, 56–90 x 48–56 μm.