Monographs Details: Fissidens acacioides var. acacioides
Authority: Pursell, Ronald A. 2007. Fissidentaceae. Fl. Neotrop. Monogr. 101 (Published by NYBG Press)
Synonyms:Fissidens acacioides Schrad., Skitophyllum accacioides (Schrad.) Bach.Pyl., Schistophyllum acacioides (Schrad.) Lindb., Conomitrium stissotheca Müll.Hal., Fissidens stissotheca (Müll.Hal.) Mitt., Fissidens stissotheca (Müll.Hal.) Mitt., Fissidens substissotheca Broth., Conomitrium substissotheca (Broth.) Paris
Description:Variety Description - Plants sordid to dark green. Stems monomor-phic, unbranched and branched, to 15 mm [1.5 cm] long x 0.4 mm wide; rhizoids basal, smooth; axillary hyaline nodules present; epidermis and outer 1-3 tiers of cortical cells small, incrassate, pigmented; inner cortical cells larger, thin-walled, hyaline; central strand present or absent. Leaves slightly crispate when dry, imbricate, in numerous pairs, lanceolate, acute to broadly obtuse, sometimes short-acuminate, 1.7-3.0 mm long x 0.6-1.0 mm wide, perichaetial leaves largest; margin elimbate; costa ending 4-18 cells below leaf apex, distal end often obscured by overlying chlorophyllose cells, usually bryoides type or sometimes variable; dorsal lamina ending at insertion, sometimes short-decurrent; vaginant laminae of cauline leaves 1/2-2/3 leaf length, acute, ± equal, ending on or near margin or free almost to costa and rounded; laminal cells distinct, eguttulate, irregularly bistratose, firm-walled, smooth, ± bulging, 8-13 pm long, juxtacostal cells in ventral and dorsal lamina and proximal parts of vaginant laminae somewhat larger. Monoicous (gonioautoicous); perigonia gemmiform, axillary; perichaetia terminal on stems and branches. Sporophytes 1-3 per perichaetium, usually numerous, reddish; seta smooth, 0.6-4.0 mm long; theca emergent to exserted, erect, radially symmetric, 0.5-1.0 mm long, stomatose or estomatose, exothecial cells quadrate to oblong, vertical walls thicker than horizontal walls; peristome anomalous, teeth divided ± 2/3 their length or undivided, often fenestrate; operculum conic, short-rostrate, 0.20.3 mm long. Spores finely papillose, 18-29 (-40) pm diam. Calyptra not seen.

Discussion:Fissidens acacioides is quite variable in leaf shape, costa length, and seta length. The three varieties recognized are based on these differences. The species is most apt to be confused with F. hydropogon. However, the leaves of F. acacioides are elimbate whereas those of F. hydropogon are limbate on the vaginant laminae of perichaetial and the subtending pair of leaves. In F. acacioides the vaginant laminae are about 2/3 the leaf length but in F. hydropogon they extend 4/5 the leaf length. Both species have immersed capsules, although some expressions of F. acacioides have exserted capsules. In F. hydropogon the capsules are at most emergent. The distal end of the costa in F. acaciodes can also be obscured by overlying chlorophyllose cells, but this is not the case in F. hydropogon. Lastly, F. acacioides is a denizen of the streams of southeastern Brazil, eastern Argentina, and Paraguay (as var. immersus) while F. hydropogon is known from a single site near Quito, Ecuador.
Distribution:Paraná Brazil South America| Rio Grande do Sul Brazil South America| Santa Catarina Brazil South America| São Paulo Brazil South America| Buenos Aires Argentina South America|