Hypnum chlorophyllum Hornschuch in C. F. P. von Martius et al., Fl. Bras. 1(2): 89. 1840; Stereophyllum chlorophyllum (Hornschuch) Mitten

Stems 6 cm, 2-4 mm wide across leafy stem. Leaves dorsal 1.3-1.6 × 0.6-0.9 mm, alar cells few, weakly differentiated, 12- 24 × 9-12 µm, walls not porose; lateral 1.5-2 × 0.6-1 mm, costa extending short distance beyond base, alar cells many, strongly differentiated, 24-89 × 14-28 µm, walls porose, medial laminal cells 89-146 × 7-12 µm. Perichaetia with leaves deeply erose. Seta 1.5-1.8 cm. Capsule 0.8-1.2 mm; operculum 0.4-0.6 mm.

Capsules mature winter. Forested sheltered gorges, rotten logs, exposed tree roots; moderate elevations (600-800 m); N.C.; Mexico (Quintana Roo); West Indies; Central America; n South America.

Pilosium chlorophyllum is rarely confused with other species in Stereophyllaceae. The species is distinctive because of its glossy, complanate-foliate plants, and dimorphic leaves, the dorsal ones symmetric and oblong-ovate, with neither a costa nor a distinctive alar region of differentiated cells, the lateral ones cultriform and oblong-lanceolate, with a short, weak costa scarcely reaching 1/3 leaf length, and a large area of enlarged, pigmented alar cells on one side of the costa. The cernuous, short-cylindric capsules have collenchymatous exothecial cells and the spores, 7-9 µm, are smaller than in other members of the family.