34. Microbryum Schimper, Syn. Musc. Eur. 10. 1860.
[Greek mikros, small, and bryon, moss]
Richard H. Zander
Phascum sect. Microbryum (Schimper) Podpera; Phascum subg. Microbryum (Schimper) Limpricht; Phascum sect. Pottiella (Limpricht) Paris; Phascum subg. Pottiella Limpricht; Pottia sect. Pottiella (Limpricht) Nyholm; Pottia subg. Pottiella (Limpricht) Brotherus
Plants in a low turf, scattered or gregarious, occasionally bulbiform, reddish brown distally, brown proximally. Stem very short, 0.2-0.4 mm, hyalodermis absent, sclerodermis absent or weakly differentiated, central strand present or absent; axillary hairs of 3-6 cells, the proximal 1-2 cells usually with thicker walls. Leaves appressed when dry, weakly spreading, tips occasionally reflexed when moist, lanceolate, elliptical or ovate, adaxial surface weakly concave to broadly channeled, short, 0.6-1.8 mm; base not differentiated, proximal margins not differentiated; distal margins recurved at mid leaf and commonly recurved to near apex, entire or rarely serrulate near apex, margins occasionally less papillose and somewhat thicker walled than medially; apex broadly acute; costa excurrent as an apiculus, mucro or short awn, occasionally only percurrent, adaxial outgrowths occasionally present as a pad of enlarged parenchymatous cells, adaxial cells quadrate or short-rectangular or elongate, in 2(4-6) rows; transverse section usually round, adaxial epidermis present, adaxial stereid band absent, guide cells 2(-4) in 1 layer, hydroid strand present, occasionally central, abaxial stereid band present, round to semicircular in sectional shape, abaxial epidermis present; proximal cells differentiated across leaf or higher medially, rectangular, 2-4:1, walls of proximal cells usually thin; distal medial cells quadrate to hexagonal or short-rectangular, occasionally rhomboidal, small to somewhat enlarged, 11-15 µm wide, 1-2:1, 1-stratose; papillae usually simple (seldom 2-fid), hollow, 1-6 per lumen, occasionally branching and tall, cell-walls thin to moderately and evenly thickened, convex on both sides. Specialized asexual reproduction absent. Sexual condition monoicous, usually paroicous, occasionally synoicous. Perichaetia terminal, interior leaves often somewhat enlarged, otherwise little differentiated. Seta very short to elongate (to 4 mm). Capsule stegocarpous or cleistocarpous, theca ovate to short elliptical, apiculate when cleistocarpous, 0.5-1.1 mm, annulus absent or of 1-2 rows of weakly vesiculose cells, persistent; operculum when differentiated low-conic, peristome teeth when present 16, irregular, often rudimentary, ligulate to triangular in shape, untwisted. Calyptra conic-cucullate, occasionally mitrate. Spores large, 20-30 µm. KOH laminal color reaction red.
Species 13 (4 in the flora): worldwide in temperate zones.
Microbryum is similar to Syntrichia in its broad leaves, single stereid band, and red reaction of the lamina to KOH, but differs in the short stems, distinctive reduction series involving the sporophyte, round to semicircular costal stereid band (reniform in Syntrichia), peristomes (when present) of 16 irregular, often rudimentary, truncate peristome teeth that are large in comparison with the size of the capsule, and operculum (when present) low-conic. Adaxial costal pads of cells are occasionally present (in M. vlassovii). Distinguishing features include variation in ornamentation and size of the spores, and collections of these monoicous taxa usually include sporophytes.