Monographs Details: Fissidens gymnostomus Brugg.-Nann.
Authority: Pursell, Ronald A. 2007. Fissidentaceae. Fl. Neotrop. Monogr. 101 (Published by NYBG Press)
Description:Species Description - Plants light to dark green. Stems monomorphic, unbranched and branched, to 6.5 mm long x 1.5 mm wide; rhizoids basal, smooth, tan; 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 crispate, somewhat inrolled from tips when dry, distant to loosely imbricate, as many as 9 pairs, oblong to lanceolate, broadly acute, most ending in a sharp, clear terminal cell, to 1.6 mm long x 0.3 mm wide, perichaetial leaves largest; margin crenulate, limbate on proximal ± 1/2 or less of vaginant laminae of most leaves, partially intralaminal, limbidial cells unistratose; costa percurrent or ending 2-3 cells below leaf apex, bryoides type; dorsal lamina narrowed to insertion; vaginant laminae of cauline leaves ± 1/2 -3/4 leaf length, acute, unequal, minor lamina ending near margin or ± 1/2 the distance between margin and costa; minor lamina rounded and free distally in perichaetial leaves; laminal cells distinct, eguttulate, unistratose, firm-walled, mammilose, 5.5-7 µm long. Monoicous (rhizautoicous); perigonial stems shorter or as long as perichaetial stems; perichaetia terminal on stems and branches. Sporophytes 1 per perichaetium, reddish; seta thick, to ± 1 mm long, not extending beyond perichaetial leaves; theca emergent, erect, radially symmetric to ± bilaterally symmetric, 0.5-0.7 mm long, stomatose, exothecial cells mostly oblong, vertical walls thicker than transverse walls; peristome absent; operculum conic, long-rostrate, 0.7 mm long. Spores smooth to finely papillose, 10-13.5 µm diam. Calyptra not seen.

Discussion:Fissidens gymnostomus is the only species of the genus known in the Neotropics to lack a peristome, a characteristic it shares with the African F scleromitrius (Besch.) Broth. In the Neotropical flora, F. gymnostomus might be confused with F. termitarum. Both species share a number of characters, i.e., leaves of nearly similar shape and size that often ending in a clear, sharp cell, mammillose laminai cells of nearly the same size, and reddish, short sporophytes. Whereas the limbidium of F. gymnostomus is found on most leaves, in F. termitarum it is restricted to the perichaetial and subtending leaves. While F. gymnostomus is eperistomate, F. termitarum is peristomate with teeth undivided or imperfectly divided.
Distribution:Minas Gerais Brazil South America|