Paraleucobryum spp.
Family: Dicranaceae
Project: Southwest Biodiversity Consortium
Plants in loose to dense tufts, whitish green, grayish green or yellowish green, glossy. Stems 1-4 cm, erect, simple or branched, rhizoids on stems below apex among leaves. Leaves subulate to narrowly lanceolate, gradually acuminate, subtubulose distally, erect-spreading to falcate-secund, especially at stem tips, little changed when dry, smooth; apices acute, sometimes deciduous; margins plane or incurved, serrate to serrulate distally to below leaf middle; laminae unistratose; costa single, percurrent, covering 1/2-2/3 of leaf base and all of subula, smooth or striate on abaxial surface, absent stereids, composed of 3-4 layers of large cells, hyaline, nonchlorophyllose cells intermingled with green, chlorophyllose cells, striations or ridges appearing as rows of teeth at high magnifications on abaxial surface of costa (P. longifolium); leaf cells pitted proximally, smooth, walls of medium thickness, median cells quadrate to rectangular, elongate proximally, alar cells inflated, extending to costa, 1-stratose, brown or sometimes hyaline. Specialized asexual propagation absent. Sexual condition dioicous; perigonia and perichaetia terminal; perigonial leaves ovate, concave, short-acuminate; perichaetial leaves with a broad base, abruptly narrowed to a long awn, inner ones sheathing. Seta solitary or rarely 2 per perichaetium, smooth, elongate, erect, straight to flexuose, twisted when dry, yellowish brown. Capsule erect to somewhat inclined, cylindric, straight, smooth, irregularly furrowed when dry, a few stomata at base, exothecial walls incrassate; annulus rudimentary; operculum rostrate, straight; peristome single, 16 lanceolate teeth, divided about halfway into 2 segments, papillose above, vertically to obliquely striate below, brown to reddish brown. Spores 22-33 µm, spherical to ellipsoidal, minutely papillose. Calyptra cucullate, smooth, naked, covering most of capsule, fugacious. Paraleucobryum is a rather peculiar member of the Dicranaceae because of its unique leaf structure. In the leaf cross section there is an adaxial and abaxial layer of hyalocysts and a median layer of chlorocysts. Sometimes a few chlorocysts are in the abaxial layer of cells in some species. Brothera and Atractylocarpus have a very similar leaf structure and are the reason that the three genera are often placed in the same subfamily, Paraleucobryoideae. Both B. H. Allen (1999) and P. Müller and J.-P. Frahm (1987) presented extensive discussion on the relationship of Paraleucobryum to other members of the Dicranaceae. They also discuss what may be heterospory or bimodal spores in P. longifolium.

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