Monographs Details: Fissidens obscurocostatus Pursell
Authority: Pursell, Ronald A. 2007. Fissidentaceae. Fl. Neotrop. Monogr. 101 (Published by NYBG Press)
Description:Species Description - Plants light to dark green, becoming rust colored with age. Stems monomorphic, unbranched to sparingly branched, to 2.8 mm long x 1.3 mm wide; rhi-zoids basal, smooth, pale brown; axillary hyaline nodules absent; epidermis and outer tier of cortical cells small, incrassate, pigmented; inner cortical cells larger, thin-walled, hyaline; central strand present. Leaves tightly inrolled when dry, distant to loosely imbricate, as many as 13 pairs, ± falcate, lanceolate, acute, ending in a single, sharp cell, to 0.8 mm long x 0.2 mm wide, perichaetial leaves largest; margin crenulate, ± serrulate at leaf apex, sometimes weakly limbate on proximal half of perichaetial and 1-2 pairs of subtending leaves, limbidial cells unistratose; costa ending several cells below leaf apex, the distal part ± obscured by overlying chlorophyllose cells, bryoides type; dorsal lamina narrowed toward insertion, ending above or at insertion; vaginant laminae of cauline leaves ± 2/3 leaf length, acute, unequal, minor lamina ending 1/2 or more the distance between costa and margin; laminal cells distinct, eguttulate, unistratose, smooth, bulging, quadrate, ± arranged in rows diverging from costa, 5.5-9 pm long, larger near base of vaginant and dorsal laminae. Monoicous? (probably rhizautoicous); perigonia not seen; perichaetia terminal on stems. Sporophytes 1 per perichaetium, yellow, darkening with age; seta smooth, 1.45 mm long; theca exserted, erect, radially symmetric, 0.5-0.6 mm long, stomatose, exothecial cells quadrate to oblong, ± collenchymatous; peristome not seen; operculum not seen. Spores smooth, 16-18 pm diam. Calyptra not seen.

Discussion:This species, endemic to Mexico, is characterized by a costa that in many leaves is obscured at its distal end by overlying bulging, chlorophyllose cells, and small, smooth, bulging laminal cells arranged in rows that more or less radiate obliquely from the coSanta The leaves are generally somewhat falcate, and when dry are tightly inrolled. The sharp, clear terminal leaf cell and weak limbidium can cause confusion with either F. elegans or F. homschuchii. The former species, however, has pluripapillose laminal cells, while the latter species has unipapillose laminal cells. The peristome has not been observed in this species, and because of this, its taxonomic position is uncertain.
Distribution:Nuevo León Mexico North America| San Luis Potosí Mexico North America| Tamaulipas Mexico North America|