Porotrichum

• Authority

  Buck, William R. 2003. Guide to the plants of central french Guiana. Part 3. Mosses. Mem. New York Bot. Gard. 76: 1-167.

• Family

  Neckeraceae

• Scientific Name

  Porotrichum

• Description

  Genus Description - Plants medium-sized to robust, rarely small, stipitate-frondose, in pale to dark green to golden, mostly stiff, often extensive colonies; primary stems creeping, secondary stems distinctly stipitate, erect to pendent, frondose, regularly to irregularly 1-2(3)-pinnate, usually complanate-foliate, the primary stem often more slender than the stipe, the ultimate branches often attenuate, often with flagellate branches, in cross-section with central strand. Primary creeping stem leaves reduced, widely spaced, appressed or with spreading apices, ovate to triangular, acuminate, not decurrent; margins subentire, usually plane, sometimes incurved; costa single, ending near or somewhat above midleaf; cells ± linear, smooth, firm- to thick-walled, ± porose; alar cells not or weakly differentiated. Stipe leaves often widely spaced, sometimes imbricate, appressed to squarrose, not complanate, ovate to triangular, acuminate or less often obtuse or acute, usually not or scarcely decurrent; margins subentire, rarely toothed, plane to incurved above or recurved below; costa single, ending near or above midleaf; cells mostly long-fusiform, smooth or rarely prorulose, firm- to thick-walled, ± porose; alar cells mostly weakly differentiated. Secondary stem leaves differentiated from those of the stipe and usually from branch leaves, typically the largest leaves on the plants, com¬planate, erect-spreading to spreading, usually oblong-ovate, obtuse-cuspidate to acute or short-acuminate, rarely plicate when dry, not or scarcely decurrent; margins mostly serrate at least above, less often throughout, the teeth 1-3-celled, plane to incurved above or recurved below; costa single, usually ending 2/3-3/4 the leaf length, projecting as a spine at apex or not; cells mostly fusiform, ca. 6-8:1, sometimes shorter or longer, smooth or prorulose, firm- to thick-walled, rarely thin-walled, often porose, often becoming shorter apically; alar cells typically not or poorly differentiated. Branch leaves erect- to wide-spreading, complanate or less often ± turgid, ovate to oblong-ligulate or rarely ± lingulate-obovate, often concave, sometimes strongly so, sometimes plicate, especially when dry, not or scarcely decurrent, not rounded to the insertion; margins typically serrate above with teeth 1-3-celled, sometimes almost to base, rarely with just a few scattered teeth, plane to incurved above, less often recurved below; costa single, ending near midleaf to ca. 5/6 the leaf length, rarely shorter, projecting as a spine at apex or not; cells mostly fusiform, ca. 6-8:1, sometimes shorter (1-2:1) to linear, smooth or prorulose, often firm- to thick-walled and ± porose, often becoming shorter in the apex; alar cells not or weakly differentiated or distinct but few. Asexual propagula common, of flagellate branches or rarely of caducous leaves; flagellate branches arising from branch apices or axils of branch leaves, with greatly reduced leaves. Dioicous or rarely autoicous. Perichaetia conspicuous, without ramenta. Setae short to elongate, mostly 0.5-3 cm long, usually smooth, rarely roughened above, stout to slender, reddish; capsules erect, cylindric, symmetric; exostome teeth on the front surface cross-striolate either only in lowermost part or well up the tooth, sometimes with overlying papillae, papillose above; endostome with a medium-high to high, mostly ± smooth basal membrane, segments mostly papillose, keeled, perforate to gaping, about as long as the teeth, cilia in groups of 1-3, papillose, shorter than the segments, or rudimentary to absent. Calyptrae cucullate, naked or sparsely hairy.

• Discussion

  Porotrichum is a genus of perhaps 20-30 species, most speciose in tropical America but with good representation in Africa and less in tropical Asia. It is characterized by strongly stipitate-frondose plants, the leaves (at least those of secondary stems above branching) are complanate, and the setae are elongate. It differs from some of the other allied genera by having mostly fusiform laminal cells that are usually firm- to thick- walled and often porose. I agree with Sastre-De Jesus (1987) in synonymizing Porothamnium with Porotrichum. Traditionally they have been segregated by Porothamnium having exostome teeth cross-striolate well up the front surface of the teeth, a high endostomial basal membrane, and well developed cilia, and Porotrichum having its exostome cross-striolate only at the base of the teeth, a lower (but still prominent) endostomial basal membrane, and no cilia. De Sloover (1983) additionally suggested that Porothamnium could be recognized by a glossy (rather than dull) seta, and plants of a darker, more metallic green. From my experience, species with better developed peristomes (i.e., Porothamnium) are mostly terrestrial or epilithic, and those with more reduced peristomes {Porotrichum) are epiphytic.