Homomallium mexicanum Cardot 1910

Homomallium mexicanum

Homomallium mexicanum Cardot, Rev. Bryol. 37: 53. 1910. Type: Mexico. Hidalgo: Cuyamaloya Station, 17 Sept 1908, Pringle, Plantae Mexicanae 10631 (syntypes: NY-3!, US!), 15250 (syntype: specimen not seen).

Plants medium-sized, in flat mats, shiny, soft, pale green to dark green. Stems to 4 cm long, creeping, elongate, irregularly pinnately branched; branches erect-ascending, somewhat curved, 2–7 mm long, rarely flagelliform; in cross section with 1–2 rows of medium-sized, thick-walled cells surrounding abruptly larger firm-walled cells, central strand of small, very thin-walled cells; pseudoparaphyllia filamentous; axillary hairs of 1 short brown basal cell and 1–2 elongate hyaline apical cells. Stem and branch leaves similar, 1–1.4 mm long, homomallous, strongly concave, ovate-lanceolate, broadly long-acuminate; margins subentire to serrulate above, entire below, usually narrowly recurved below, plane above; costa short and double; cells long-hexagonal, flexuose, 40–70 μm long at midleaf, mostly 5–6 μm wide, as short as 20 μm long in the acumen, smooth; alar cells subquadrate to oblate (especially along the margins) in 6–8 rows, extending up the margins by 20–30 cells. Perichaetial leaves erect, oblong-lanceolate, convolute, gradually narrow-acuminate; margins subentire. Setae 0.5–1.5 cm long, reddish; capsules 1.3–1.5 mm long, suberect to inclined, cylindrical; annulus of 1 row of thick-walled cells; operculum ˜0.4 mm long, mostly obliquely short-rostrate; exostome teeth cross-striolate below, coarsely papillose above, trabeculate at back; endostome yellowish, papillose throughout, with a high basal membrane, segments keeled, perforate, cilia mostly in pairs. Spores 15–20 μm in diameter. Calyptrae cucullate, naked, smooth.

Distribution and ecology: Northern Mexico; also in southwestern United States; growing on bases of hardwood trees, logs, and rocks, mostly at (1500–)2000–2700 m.

Illustrations in publications: Fig. 755 in Ando (1994: 1016).

Discussion: When sterile, the plants might be confused with Pylaisia because of the numerous alar cells. However, the shorter apical laminal cells are decidedly different than those in that genus. When sporophytes are present (frequent), the inclined, asymmetric capsules separate it from the erect, symmetric capsules of Pylaisia. Homomallium mexicanum differs from H. adnatum (Hedw.) Broth., of eastern North America, by its larger size (leaves greater than 1 mm long), longer apical laminal cells, and recurved lower leaf margins.

Specimens examined: MEXICO. Durango: Along Hwy. 40, W of Durango, near Km 103, 23°48'N, 105°23'W, ˜2355 m, King & Garvey B311 (MO, NY). Guanajuato: Sierra de Pénjamo, 24 km SW de Cuerámaro, 20°35'N, 101°45'W, Delgadillo 5825 (MEXU, NY). Hidalgo: Only the type seen.

Homomallium mexicanum là một loài Rêu trong họ Hypnaceae. Loài này được Cardot mô tả khoa học đầu tiên năm 1910.