Plants to 12 × 1.5-3.5 mm. Stem branched; axillary hyaline nodules absent; central strand present. Leaves as many as 28 pairs, sometimes ± undulate, oblong, obtuse-apiculate to acute, to 2.4 × 0.3-0.4 mm; dorsal lamina narrowed proximally, ending before or at insertion; vaginant laminae ¹/2-²/3 leaf length, acute, ± unequal, minor lamina ending near margin; margin evenly crenulate-serrulate but irregularly serrate distally; costa ending 6-16 cells before apex, covered and obscured above by chlorophyllose cells, taxifolius-type; lamina cells irregularly 2-stratose, smooth, bulging, firm-walled, irregularly rounded-hexagonal, 7.5-10 µm. Sexual condition gonioautoicous and cladautoicous; perigonia gemmiform, axillary, and on short branches; perichaetia on short axillary branches near proximal ends of stem. Sporophytes 1 per perichaetium. Seta 1.5-5.5 mm. Capsule theca 0.8-2.1 mm, erect, radially symmetric or nearly so; peristome taxifolius-type; operculum long rostrate, 0.6-0.9 mm. Calyptra cucullate, smooth, 1.5 mm. Spores 13-18 µm.

Particularly around bases of trees, also rocks, mostly limestone, infrequently decaying wood; Ont., Que.; Ala., Ark., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Miss., Mo., N.H., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va., Wis.; Mexico (San Luis Potosí, Tamaulipas).

Fissidens subbasilaris is distinguished, even in the field, by a costa obscured by chlorophyllose cells distally, and short perichaetial branches in the axils of proximal leaves. The plants are typically dark-green and often tinged with red.