Stem rounded-pentagonal in section. Leaves flat but narrowly keeled along costa, long-ligulate, distal margins plane, entire (or tattered by fragmentation), not bordered; apex narrowly rounded, blunt, keeled; basal cells differentiated across leaf base, not running up margins, not distinctly enlarged submarginally; distal laminal cells with a massive multiplex papillae over each lumen; mucro short-conic, of ca. 3 cells. Sterile in range of the flora.

Soil, rock, calcareous substrates; La., Tex.; Mexico; West Indies; Central America (Belize, Guatemala, Honduras).

Trichostomum portoricense is a distinctive species with no immediate relatives in the genus. The deep, narrow groove down the adaxial surface of the leaf is reminiscent of that of species of Barbula or Anoectangium. The massive, cap-like papillae are similar to those of Tuerckheimia, but the long-ligulate leaf shape of T. portoricense is diagnostic. The leaf lamina fragments easily in patches, and doubtless figures in asexual reproduction. The distribution was recently summarized by P. M. Eckel (2003).