Leucobryum Moss

Leucobryum albidum characteristically occurs in small, low cushions, usually no more than 10 cm in diameter, and frequently bears sporophytes. Of the 1035 collections examined, 632 (61 percent) had sporophytes. Leucobryum albidum is sometimes difficult to separate from small plants of L. glaucum. Some authors have used the number of leucocysts, as seen in transverse section, on both sides of the chlorocyst layer on thicker, lateral regions of costa to separate these species. However, this character varies widely on plants from the same colony and even on different sides of the same leaf. There is also no consistent pattern for these species across the geographical range, and correlation with other characters such as stem height and length of limb to length of sheath is inconclusive. The most satisfactory criteria for recognizing L. albidum are its generally compact, short cushions and leaves 2-4 mm with reflexed limb usually shorter than the sheath. E. Patterson et al. (1998) in a study of Leucobryum from a limited area near Durham, North Carolina, using nuclear ribosomal DNA extracts from plants of various sizes, demonstrated that two haplotyes were present, and that L. albidum (small plants) is genetically discontinuous with L. glaucum (large plants). Leucobryum incurvifolium Müller Hal. [= Terrestria incurvifolia ( Müller Hal.) W. L. Peterson] was reported from Florida (W. L. Peterson and A. J. Sharp 1980). However, the two collections cited from Florida appear to be nothing more than a variation of L. albidum. They do not have the distinct cucullate, hyaline-apiculate leaf tips characteristic of L. incurvifolium (Peterson 1994).

Plants in low, compact cushions or turfs. Stems less than 1 cm tall (rarely to 4.5 cm). Leaves 2-4(-6) mm, limb subtubulose, erect to wide-spreading, straight, apex apiculate, entire, speading from oblong-obovate sheath, shorter than (rarely equal to) the length of the sheath; costa in transverse section near base showing lateral, thicker regions composed mostly of 2(-3) layers of enlarged leucocysts on both sides of the central layer of chlorocysts, and a central, thinner region composed of 1 layer of smaller leucocysts on both sides of the chlorocyst layer; lamina narrow, 8-11 cells wide. Specialized asexual reproduction by small leaf-like gemmae on minute, forked branches at stem tip or on pseudopodium-like branches and by caducous leaves with rhizoids at leaf apex. Seta 8-12 mm, brown to reddish. Capsule strongly inclined and curved when dry and empty, sometimes slightly strumose, 1.2-1.8 mm, red to reddish brown; operculum 1-1.3 mm; peristome teeth dark red. Spores minutely papillose, 11-16 µm.

Dicranum albidum P. Beauvois, Prodr. Aethéogam., 52. 1805