Monographs Details: Pylaisiadelpha
Authority: Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part Two: Orthotrichales to Polytrichales. Mem. New York Bot. Gard. 69 (2)
Description:Genus Description - Plants small and slender to medium-sized, in flat, shiny, green or yellowish mats. Stems creeping, freely and regularly pinnate-branched. Leaves often complanate, ± secund, at least at the tips, oblong-lanceolate to oblong-ovate or elliptic, gradually or abmptly acuminate; margins usually recurved or reflexed below, sermlate toward the leaf tips; upper cells linear-rhomboidal, smooth; alar cells subquadrate in small triangular areas, usually with some cells at the extreme base inflated and hyaline or yellowish in 1-2 rows. Setae elongate, smooth; capsules erect or nearly so, symmetric, and oblong-cylindric; operculum short- to long-rostrate; exothecial cells not collenchymatous; exostome teeth with a median zigzag line, cross-striolate below, bordered, trabeculate at back; endostome with a high basal membrane, keeled segments, and cilia none, single, or paired. Calyptrae cucullate.
The leaves, sometimes complanate, are secund, at least at the tips. The alar cells may be abmptly inflated in 1-2 rows or only slightly enlarged at the extreme angles. The exostome teeth are not furrowed, as also in Sematophyllum, and the exothecial cells lack the corner thickenings of that genus.
Pylaisiadelpha Card. 1910 is an older name than Brotherella Loeske ex Fleisch. 1914, which it replaces, at least in part (Buck, 1984c; Ando et al., 1989). Brotherella differs in its larger size, leaves not or weakly falcate, alar cells better differentiated, with only a few subquadrate cells above them, capsules inclined to subhorizontal, peristome better developed (and perfect), and spores smooth or less papillose. The Mexican species do not sort well into those categories, although they seem, in most respects, closer to Pylaisiadelpha. The wide-ranging, temperate species, B. recurvans (Mx.) Fleisch. and its allies very likely deserve segregation from Pylaisiadelpha, and P. deplanatula may be better placed in Brotherella. According to Ando et al. (1989), Pylaisiadelpha belongs in the Hypnaceae and Brotherella in the Sematophyllaceae.