Brachythecium rivulare Schimp.

Authority

Buck, William R. 1998. Pleurocarpous mosses of the West Indies. Mem. New York Bot. Gard. 82: 1-400.

Family

Brachytheciaceae

Scientific Name

Brachythecium rivulare Schimp.

Description

Species Description - Plants medium-sized to ± robust, in ± lustrous, ± soft, green to yellow-green, dense, often extensive tufts. Stems creeping, inconspicuous, to ca. 10 cm long, irregularly but freely branched, the primary branches ascending to erect, ca. 1.5-2.5 cm long; in cross-section with 1-2 rows of small thick-walled cells surrounding abruptly larger thinner-walled cells, central strand of small thin-walled cells; pseudoparaphyllia foliose; axillary hairs with a single short brown basal cell and a single elongate hyaline distal cell. Primary and secondary branch leaves somewhat differentiated, primary branch leaves erect when dry, erect-spreading when moist, oblong-ovate, gradually or sometimes ± abruptly broadly acuminate, the apex usually not twisted, (1.5-) 1.8-2.5 mm long, ± concave, weakly plicate, strongly decurrent; margins serrulate almost throughout, plane; costa single, tapering distally, ending ca. 3/4 the leaf length; cells linear, straight to subflexuose, smooth, firm-walled, becoming broader and thicker-walled toward the insertion; alar cells ± abruptly differentiated, conspicuous in broad decurrencies, cells short-oblong, ± inflated. Secondary branch leaves crowded, erect when dry, erect-spreading when moist, oblong-lanceolate, 1-1.5(-2) mm long, gradually acute to broadly acuminate, ± concave, not or weakly plicate, inconspicuously decurrent; other details as in primary branch leaves. Asexual propagula none. Dioicous, or rarely autoicous. [Sporophytes unknown in the West Indies; description from North American material.] Perichaetia somewhat conspicuous; leaves spreading from an erect, oblong base, to ca. 3.75 mm long, ± abruptly long-acuminate, concave; margins ± crenulate throughout, plane; costa single, ending below midleaf, near apex of base, sometimes absent in outermost leaves; cells linear, smooth, firm-walled, becoming shorter and broader toward the insertion; alar cells not differentiated. Setae elongate, roughened throughout, reddish, 1.5-2.5 cm long, straight to subflexuose, not or only slightly twisted; capsules inclined to horizontal, asymmetric, cylindric, 2-2.5 mm long, dark-brown; exothecial cells subquadrate, thick-walled, scarcely differentiated at the mouth, stomata round-pored; annulus of (1-) 2(-3) rows of rectangular, thick-walled cells, narrower than those of the exothecium, tardily deciduous; operculum conic-apiculate, ca. 1.2 mm long; columella broadly oblong, ca. as long as the urn; exostome teeth reddish brown, triangular, scarcely shouldered, narrowly bordered, on the front surface cross-striolate below, finely papillose and pale above, trabeculate at back; endostome finely papillose, with a high basal membrane, segments keeled, perforate, shorter than the teeth, cilia in groups of 2-3. Spores spherical, finely papillose, 15-22 µm diam. Calyptrae cucullate, naked, smooth.

Discussion

4. Brachythecium rivulare Schimp. in Bruch, Schimp. & W. Giimbel, Bryol. Eur. 6(fasc. 52-54, Monogr. 1): 17. 1853; Hypnum rivulare (Schimp.) Bruch in Wils., Bryol. Brit. 346. 1855, hom, illeg., non Brid., Musc. Rec. 2(2): 117. 1801 [=Brachythecium albicans (Hedw.) Schimp.]. Plate 95, figures 9-16 Discussion. Brachythecium rivulare is recognized by more or less erect primary branches growing in wet habitats. The alar region is strongly broad- decurrent and abruptly differentiated, with inflated alar cells filling the decurrencies. It is known from a couple of localities in La Vega Province, Dominican Republic. The species is a good example of a north-temperate disjunct to the higher elevations of Hispaniola. Often these species are further represented in the northern Andes, but not in this case.

Distribution

Range. North America, from Newfoundland to British Columbia and Alaska in the north, and North Carolina and Arkansas to New Mexico in the south, Europe, central and eastern Asia; Hispaniola (Dominican Republic); usually growing in or near waterfalls or seepy areas, in the West Indies at 1500-2200 m.

North America| Europe| Asia| Dominican Republic South America| West Indies|