Monographs Details: Fabronia
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 very small, in soft, silky-green mats. Stems fragile, sparsely branched, in section 6-8 cells across, all cells ± thin-walled with scarcely any differentiation in size but slightly larger toward the outside; pseudoparaphyllia foliose; branches usually short, ± terete. Leaves loosely appressed when dry, spreading when moist (branch leaves somewhat smaller and less acuminate than stem leaves), narrowly lanceolate to ovate, gradually or abruptly acuminate, often piliferous; margins plane, entire, denticulate, dentate, or ciliate-dentate; costa slender, usually extending to about the midleaf, sometimes ending in a small spine; upper cells short- to long-rhomboidal, smooth, mostly thin-walled except at the tip ofthe costa and in the acumen, with conspicuous primary utricles; alar cells quadrate. Autoicous. Perichaetial leaves broader than vegetative leaves, often serrate-dentate. Setae erect, smooth, yellowish; capsules ovoid to pyriform, often flaring at the mouth on aging; annulus none; operculum umbonate to mammillate; exothecial cells ± isodiametric to short-rectangular with strongly wavy walls except at the mouth where the cells are ± narrowly rectangular with straight walls; peristome single (consisting of exostome only) or absent, inserted below the mouth, incurved when moist, erect to spreading when dry, the 16 teeth usually fused in pairs, broadly lanceolate and blunt, red-brown, with a ± straight center line and large plates on the outer surface, densely papillose-striolate throughout; columella short. Spores smooth to coarsely papillose.
Fabronia is taxonomically difficult. Few characters are stable. This is especially true of marginal toothing, yet many species have been described on that basis alone. In Mexico the variations are such that all the species can be confused. I have relegated many names to varietal status or complete synonymy. I rationalize that approach only by assuming that early workers describing species as new had access to few collections and were unaware ofthe great morphological variability. Buck (1983a) treated the South American Fabroniae in considerable detail. That treatment is useful in evaluating the Mexican species as well.