Brachymenium acuminatum Harv. in Hook., Icon. Pl. 1: 19. 1836.
Protologue: East Indies, Harvey.
Brachymenium filescens Bartr., J. Wash. Acad. Sci. 21: 292. 1931. Protologue: Costa Rica. Province of Alajuela, Cebadilla, alt. 700 m., Nov. 14, 1928, Valerio 209 (FH, US).
Plants minute, yellow-green, gregarious or in loose tufts. Stems slender, 2–10 mm long, epidermal cells quadrate, sparsely tomentose at base; rhizoids sparse at base, reddish brown, papillose roughened. Leaves 0.5–0.8 mm long, stiffly erect-appressed to imbricate when dry, concave, ovate to ovate-lanceolate; apices shortly acuminate; margins weakly bordered by long, narrow cells, entire, erect above, slightly reflexed below; costa percurrent to shortly excurrent, ventral superficial cells at base quadrate to rectangular; leaf cells lax and thin-walled throughout, upper cells elongate-rhomboidal, 40–90 x 10 μm, alar cells short-rectangular, 20–30 x 16–20 μm. Dioicous. Setae 10–30 mm long, red. Capsules 1.5–2.0 mm long, red, claviform to elongate-pyriform, constricted at neck, erect; opercula 0.3–0.5 mm long, conic; annuli compound, revoluble; exostome teeth reddish brown, thickly papillose, endostome yellowish, basal membrane to ½ the exostome teeth length, segments rudimentary to absent, cilia rudimentary to absent. Spores 10–14 μm, smooth to obscurely roughened. Calyptra not seen.
1. Brachymenium acuminatum Harv. in Hook. 尖叶短月藓 jian ye duan yue xian Icon. Pl. Rar. 1: 19. 1836. Gemmabryum acuminatum (Harv. in Hook.) Spence & Ramsay, Phytologia 87: 65. 2005. Type: East Indies, Harvey s.n. Plants small, to 5 mm high, grayish green to yellowish green, in dense tufts. Stems short, erect or nearly so, with numerous innovated branches and rhizoids at base. Leaves dense, in multiple rows, imbricately appressed, ovate-lanceolate, keeled, ca. 1.0 mm × 0.5 mm; margins plane, entire or serrulate in the upper part; costae strong, excurrent into long awns; leaf cells thin-walled; alar cells distinctly differentiated, quadrate or shortly rectangular, gradually becoming rhomboidal upwards; apical cells vermicular, thick-walled. Dioicous. Perichaetial leaves triangularly lanceolate, larger than the branch leaves. Setae erect, 8–20 mm long; capsules erect or slightly inclined, pyriform or ovoid; neck short; mouth narrowed; opercula conic, shortly apiculate; endostome segments rudimentary, basal membrane ca. 1/2 the height of teeth; cilia rudimentary or absent. Spores 11–17 µm in diameter.
The glossy, light green, concave leaves, with lax, elongate upper leaf cells and generally strongly differentiated basal cells will separate G. acuminatum from other species of the genus. Although the leaf is generally concave, above the base, when cut in cross-section the entire lamina is broadly recurved. This is apparently due to a slight thickening of the dorsal cell facies.
Plants small, forming loose turfs, light green to yellowish green, glossy; terricolous. Stems (2-)5-10 mm long, sparsely radiculose below; in section cortical cells in 2-4 rows. Leaves erect-appressed, little altered dry, concave; ovate to ovate-acuminate or ovate-lanceolate, 0.5-0.8 mm long; apex acute to acuminate; base flat, not concave; margins erect, entire. Costa short-excurrent, mucro 0.1-0.2 mm long; in section subround, ventral cells 2, large, thin-walled, dorsal substereid band 2 cells thick, dorsal surface cells undifferentiated. Upper laminal cells mostly 6-10: 1, fusiform to linear-rhomboidal, ± sinuolate, (50-)75-150 µm long, 12-18 µm wide, dorsal surface weakly thickened; basal cells generally distinct,quadrate to short-rectangular, 1-2: 1, thin-walled. Perichaetial leaves triangular, ± 1 mm long. Seta (6-)10-15(-22) mm long, yellowish; capsule suberect to inclined or almost horizontal, clavate to cylindrical-pyriform or occasionally smaller and pyriform, 2.5-3.5 mm long, yellowish, neck sulcate, to 1 mm long; exothecial cells subrectangular, walls ± wavy, 1-2 rows of transversely rectangular cells at mouth; peristome teeth 200-300 µm long, endostome with basal membrane 175-200 µm high, segments rudimentary; spores round, 16-18 µm, green, weakly papillose.
Plants in loose turfs, yellowish green, glossy. Stems 2-10 mm long. Leaves erect-appressed, concave, ovate to ovate-acuminate, 0.5-0.8 mm long; margins entire; costa short-excurrent. Upper laminal cells fusiform to linear-rhomboidal; basal cells distinct, quadrate to short-rectangular. Capsule inclined to horizontal, clavate to cylindrical-pyriform; endostome segments rudimentary. Recognised by the light green, glossy plants with concave leaves, lax, elongate upper laminal cells and strongly differentiated basal cells.
Brachymenium acuminatum has been reported from eastern and southern Africa, South America, India, southeast Asia and Australia. In southern Africa the species is found in the northern, central, southern and eastern Transvaal, Swaziland, Natal and Lesotho. A few specimens have also been collected in the northwestern and southwestern Cape, eastern Orange Free State, central South West Africa/Namibia and Botswana.