Haplodontium crassinervum Herz., Biblioth. Bot. 87: 78. 1916. Syntypes: BOLIVIA. "Bei den Tunariseen, ca. 4400 m, [Herzog] 4840 & 4774" (lectotype BM!-4840).
The type specimen is stiffly robust and reddish to reddish-brown, with erect and imbricate leaves. Stems are highly branched by subfloral innovations although a few forks are present; perichaetia seem to be consistently terminal. Perigonia were not observed. Bryum crassinervum is similar to B. alpinum With, in having ovate-lanceolate leaves, strong costae ending near the apices, and long, narrow cells. It is distinguished by the very highly branched stems that make the perichaetia seem lateral. Sporophytes are not known. The gametophytes of B. crassinervum are, however, very different from those of any species of Mielichhoferia or Schizymenium.