BFNA Title: Macrocoma
Macrocoma - Orthotrichaceae
4. Macrocoma (J. K. A. Müller) Grout, Bryologist 47: 4. 1944 * [Greek macro-, long, and kome, maine, alluding to long hairs on calyptrae of some species]
Macromitrium sect. Macrocoma J. K. A. Müller, Bot. Zeitung (Berlin) 3: 522. 1845
Dale H. Vitt
Plants slender to filiform, mats on trees and rocks. Stems creeping with numerous lateral ascending branches. Branch leaves closely erect-appressed, not contorted when dry, erect-spreading when moist, up to 2 mm, lanceolate to ovate-lanceolate, narrowly obtuse, acute, or bluntly acuminate, carinate, rhizoids often produced on the abaxial side of the costa; margins ± plane, entire; costa percurrent, prominant; distal cells small, rounded-quadrate, bulging, smooth or papillose; basal cells rounded to elliptic, bulging, papillose-mammillose. Perichaetial leaves slenderly acute. Sexual condition goniautoicous. Seta smooth, to 7 mm, dextrose. Capsule exserted, oblong-cylindric to fusiform, ± plicate above or smooth; stomates superficial; peristome single or lacking; consisting of 16 pale, short, blunt teeth or a low, papillose membrane. Calyptra mitrate, long elliptic-conic, ± hairy, completely covering capsule, smooth. Spores rather large, isomorphic.
Species 11 (1 in the flora); in higher elevation scrub forests; North, Central and South America, West Indies, Asia, Africa (including Madagascar), Australia, Pacific Islands (Hawaii, New Zealand).
In addition to the rounded basal cells, characters of the genus include the slender, irregularly branched stems, leaves erect-appressed when dry, capsule cylindric, peristome often reduced, and calyptra long conic-elliptic.
1. Macrocoma tenuis (Hooker & Greville) Vitt, Rev. Bryol. Lichénol. 39: 217. 1973
Orthotrichum tenue Hooker & Greville, Edinburgh J. Sci. 1: 120. plate 5. 1824
Subspecies 2 (1 in the flora): North America; Central America; South America; West Indies; Asia; s Africa; Pacific Islands (New Zealand); Australia.
1a. Macrocoma tenuis subsp. sullivantii (J. K. A. Müller) Vitt, Bryologist 83: 405--436. 1980
'Macrocoma sullivantii J. K. A. Müller, Bot. Zeitung (Berlin) 20: 361. 1862
Plants slender. Branch leaves 0.7--1.2 mm, acute to narrowly obtuse; cells papillose, up to 22 µm, margins of distal cells bulging. Perichaetial leaves longer. Seta 4--6.5 mm. Capsule 1.3--2 mm; exothecial cells not or slightly differentiated; peristome single, consisting of low, densely papillose membrane. Calyptra obscurely plicate, mitrate but many times splitting by single cleft along one rib. Spores 33--42 µm.
Dry mountain tops and slopes of the southern Blue Ridge escarpment, abundant, sometimes covering entire tree trunks of Pinus, Juniperus, and Quercus; 600 m and above; Ga., N.C., S.C., Tenn.; Mexico; West Indies; South America; Asia (China, Japan, Korea, Taiwan).
Macrocoma tenuis subsp. sullivantii differs from other species in the Orthotrichaceae by having slender, creeping stems with erect branches. The leaves are erect-appressed, and the basal cells of the leaves are rounded-quadrate. It is very closely related to a Mexican species, M. orthotrichoides, which differs in having a peristome and its sparsely hairy calyptra. Macrocoma tenuis subsp. tenuis is Old World in distribution.