Plaubelia

Plants small, turf-forming or loosely cespitose, green distally, sometimes brown proximally. Stems often branching, to 4 mm, hyalodermis absent, sclerodermis weak, central strand strong; rhizoids sparse; axillary hairs of up to 5 cells, the basal 1–2 yellow. Cauline leaves smaller proximally, distally much larger, rosulate, crowded, incurved to spreading, often tubulose and incurved-contorted when dry, widespreading when moist, spathulate to oblong-ligulate; base little different in shape; margins incurved, involute or sometimes plane, entire or distantly denticulate above; apex rounded-acute to broadly rounded-obtuse, usually apiculate; costa short-excurrent, percurrent or ending up to 4 cells before the apex, adaxial surface of bulging cells, adaxial epidermis of bulging or mammillose cells, abaxial epidermis weakly differentiated, 1–2 stereid bands, guide cells 2–4 in 1 layer, hydroid strand often present; basal cells not differentiated or distinct in a small medial group or across the base, quadrate to short-rectangular, hyaline to yellowish; distal laminal cells rounded-hexagonal, walls evenly thickened, adaxially bulging-mammillose, abaxially nearly plane; distal laminal papillae often absent, or solid, small, simple, 1–2 per lumen abaxially or occasionally on both sides. Specialized asexual reproduction absent [gemmae present in leaf axils]. Sexual condition dioicous. Perichaetia terminal, leaves ovate-lanceolate to ligulate, shorter than stem leaves. Seta 1–8 mm. Capsule red to yellow-brown, ellipsoidal, operculum rostrate, peristome of 16 red, spiculose, long-linear teeth, not twisted, basal membrane absent. Calyptra cucullate. Spores lightly papillose, 8–10 µm. Laminal KOH color reaction in proximal leaves often orange-brown, in distal leaves yellow.

Distribution

sw, se United States, Mexico, West Indies, Central America, South America (Brazil, Venezuela), Asia (Burma), s Africa.

Discussion

Species 3 (1 in the flora).

As discussed by R. H. Zander (1993), the circumscription of the genus Hyophila is unsatisfactory, being both artificial (e.g., absence of peristome) and polyphyletic. The genus Plaubelia is separated from Hyophila mainly by the presence of a peristome. The two genera are related by the adaxially bulging, abaxially flat laminal cells, spathulate-oblong leaves, poorly differentiated basal cells, similar clavate gemmae (in exotic species) and other characters. The single abaxial stereid band of Plaubelia sprengelii was once an important basis for the genus, but with the inclusion of var. stomatodonta with its second stereid band into the variation of the species (Zander 1983), the generic distinction becomes more problematic.