21. Fissidens obtusifolius Wilson, London J. Bot. 4: 196, plate 9, fig. b. 1845.
Fissidens obtusifolius var. kansanus Renauld & Cardot; F. obtusifolius var. marginatus Flowers
Plants to 8 × 1.5 mm. Stem branched; axillary hyaline nodules absent; central strand weak or absent. Leaves as many as 20 pairs, broadly ovate to oblong, rounded to obtuse, infrequently weakly apiculate in distal leaves, to 1.3 × 0.4 mm; dorsal lamina narrowed proximally, ending at or before insertion; vaginant laminae ± 1/2-4/5 leaf length, ± equal, minor lamina ending on or near margin; margin ± entire, elimbate or weakly to strongly limbate, limbidium restricted to proximal parts of vaginant laminae of perichaetial, perigonial and subtending leaves, or present along entire length of vaginant laminae of most leaves, or variable on all laminae of larger leaves, often intralaminal in proximal parts of vaginant laminae, often spurred in vaginant laminae; costa ending 2-11 cells before apex, often spurred above, bryoides-type; laminal cells 1-stratose, distinct, smooth, ± bulging, irregularly quadrate to hexagonal, 6-15 µm. Sexual condition cladautoicous, gonioautoicous, and possibly rhizautoicous; naked archegonia occasionally in axils of distal leaves. Sporophytes 1 per perichaetium. Seta to 3.5 mm. Capsule theca exserted, ± erect, radially symmetric, to 0.8 mm; peristome bryoides-type; operculum to 0.3 mm. Calyptra cucullate, smooth, 0.5 mm. Spores 20-29 µm.
Typically on limestone and limestone bearing sandstone along streams and waterfalls, often near the high-water level, sometimes inundated, infrequently on bricks; Ont.; Ala., Ark., Colo., Conn., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mass., Mich., Minn., Mo., Nebr., N.Y., Ohio, Okla., Pa., Tenn., Tex., Utah, Va., W.Va., Wis.
The ovate to oblong, rounded to broadly obtuse leaves on which the limbidium can be quite variable distinguish Fissidens obtusifolius. It has been confused with an expression of F. bryoides that typically occurs on acidic stones and rocks aside streams, and with expressions of F. sublimbatus (R. A. Pursell 1997). Both of those species have highly variable limbidia. The former, however, has lanceolate to ligulate, acute to obtuse-apiculate leaves in which the apiculus is poorly developed. The latter has smaller laminal cells and ovate to lanceolate, rounded to obtuse-apiculate leaves in which the apiculus is a single sharply pointed cell.