Monographs Details: Macromitrium
Authority: Sharp, Aaron J., et al. 1994. The Moss Flora of Mexico. Part Two: Orthotrichales to Polytrichales. Mem. New York Bot. Gard. 69 (2)
Description:Genus Description - Plants slender to robust, often yellow- to olive-green above, in dense, spreading, tomentose, green, reddish-rusty-brown mats on rocks and trees. Stems creeping, with numerous, ascending to erect, simple or forked branches. Leaves contorted, spirally-twisted, or crisped-flexuose, rarely loosely erect-appressed, with apices inrolled to twisted when dry, erect-spreading to squarrose-recurved when moist, keeled, linear-lanceolate, ligulate, oblong, ovate-oblong, or lingulate, rounded-obtuse, acute, or long-acuminate, sometimes cuspidate, apiculate, subulate, or long-awned, rarely fragile-tipped; margins entire, crenulate to serrate, erect, plane, or reflexed-recurved; costa single, strong, excurrent or ending in or near the apex; upper cells rounded to rectangular-elliptic, ± thick-walled, flat to strongly bulging, smooth or with conic or rounded papillae; basal cells elongate, thick-walled, smooth or tuberculate, with sinuose lumina. Autoicous or dioicous, sometimes pseudautoicous. Perigonia budlike, axillary or on short branches, often produced by dwarf male plants. Perichaetial leaves sometimes longer than other leaves. Setae smooth or papillose, elongate, erect to flexuose; capsules long-exserted, erect, ovoid, elliptic, or cylindric, smooth to 8-ribbed the entire length, usually not constricted below the mouth, abruptly to gradually contracted to the seta through a short neck; stomata superficial, often with guard cells poorly differentiated, in the lower portion ofthe urn; annulus usually of 1-3 rows of thin-walled, hyaline cells; operculum conic, long-rostrate; peristome double, single, or lacking; exostome teeth 16, often united in 8 pairs or membranous, densely papillose or papillose-striate, erect or recurved; endostome, when present, consisting of a delicate, sparsely papillose membrane, rarely divided into segments. Spores isosporous or anisosporous, moderate-sized to large, papillose. Calyptrae conic-mitrate, laciniate or many lobed, rarely slit up 1 side, plicate, smooth, sometimes hairy.
In Mexico, there are 10 species of Macromitrium, of which M . guatemaliense and M . cirrosum are by far the most common. Three groups of species can be recognized: (1.) Macromitrium altituberculosum, M.fragilicuspis, M . guatemaliense, and M. contextum are large and irregularly branched, with fairly broad leaves and basal marginal borders toothed near the insertion; the basal cells tend to be strongly tuberculate and the leaves irregularly twisted. (2.) Macromitrium cirrosum, M . longifolium, and perhaps M . punctatum have similar leaf orientation and size, but the leaves are narrower and often more acuminate, the basal cells not as strongly tuberculate or even smooth, and the basal border entire. (3.) Macromitrium microstomum, M. richardii, and M . sharpii are smaller, more regularly branched from a creeping stem (approaching Groutiella), with leaves contorted and inrolled at the tips and having smooth or slightly tuberculate basal cells and entire basal margins.