Paraleucobryum (Limpricht) Loeske, Allg. Bot. Zeitschr. Syst. 13 (10): 162. 1907.
Greek para, similar to; Leucobryum, a genus of mosses in the Leucobryaceae
Robert R. Ireland
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, lacking 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 lacking. 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.
Species 3--4 (2 in the flora): Mexico, North America, Europe, Asia.
The genus 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. Allen (1999) and P. Müller and J.-P. Frahm (1987) present 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.
Allen, B. 1999. The genus Paraleucobryum (Musci: Dicranaceae) in Maine. Evansia 16(4): 174--178. Barnes, C. 1958 (1959). The genus Paraleucobryum. The Bryologist 61 (4): 335--339. Crum, H. A. and L. E. Anderson. 1981. Mosses of Eastern North America. Vol. 1. Columbia University Press, New York. Ireland, R. R. 1982. Moss Flora of the Maritime Provinces. National Museums of Canada, Natl. Mus. Nat. Sciences, Publs. in Botany, No. 13. Ottawa. Müller, P. and J.-P. Frahm. 1987. A review of the Paraleucobryoideae (Dicranaceae). Nova Hedwigia 45(3-4): 283--314. Ireland, R. R. 1994. Paraleucobryum. In: A. J. Sharp, H. Crum and P. M. Eckel, eds. The Moss Flora of Mexico, Part 1. Sphagnales to Bryales. Mem. New York Bot. Gard. 69: 147--148. Bronx. Lawton, E. 1971. Moss Flora of the Pacific Northwest. Hattori Botanical Laboratory. Nichinan. Williams, R. S. 1913. Dicranaceae. N. Amer. Flora 15(2): 77--166.