Leptodictyum riparium (Hedw.) Warnst.

  • Authority

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

  • Family

    Amblystegiaceae

  • Scientific Name

    Leptodictyum riparium (Hedw.) Warnst.

  • Description

    Species Description - Plants small to medium-sized, in dull or lustrous, soft to flaccid, yellow-green or sometimes bright-green, thin mats. Stems creeping or floating, to ca. 30 cm long, but often ca. 5-10 cm, irregularly and freely branched, the branches prostrate (if terrestrial) or ascending (if aquatic); in cross-section with 1-3 rows of small firm-walled cells, the outer row (sometimes stripping off with dissection) often with thin external walls, surrounding larger scarcely thinner-walled cells, central strand small, of small thin-walled cells; paraphyllia absent; pseudoparaphyllia foliose, small; axillary hairs with 1(-2) short brown basal cells and (2-)3-5(-7) very elongate hyaline distal cells. Stem and branch leaves similar, mostly wide-spreading, sometimes erect (in emergent aquatic forms), distantly spaced, ovate-lanceolate to oblong-lanceolate, (0.8-) 1.7-3(-4.5) mm long, long-acuminate; margins entire or subserrulate at apex, plane; costa single, slender, ending ca. 2/3 the leaf length; cells long-hexagonal to linear, 6-10:1, smooth, thin-walled, becoming shorter in the acumen, becoming noticeably laxer and broader in large areas toward the insertion; alar cells not or poorly differentiated in 2-3 rows in the extreme angles. Asexual propagula none. Autoicous. Perichaetia enlarged, conspicuous; leaves erect, oblong-ovate, 1.4-2.1 mm long, abruptly short-acuminate; margins entire or subserrulate above, plane; costa single, extending to base of the acumen; cells linear, subflexuose, smooth, becoming shorter and broader toward the insertion. Setae elongate, smooth, reddish brown to yellow, 1-2(-3) cm long, slightly twisted when dry; capsules suberect to horizontal, arcuate, asymmetric, cylindric, 1-2.5 mm long, constricted below the mouth when dry; exothecial cells short-rectangular, firm-walled, not collenchymatous, stomata long-pored; annulus of 2-3 rows of elongate, firm-walled cells, tardily deciduous; operculum conic-apiculate to short-rostrate; exostome teeth yellow-brown, shouldered, bordered, on the front surface cross-striolate below, coarsely papillose above, trabeculate at back; endostome papillose throughout, with a high basal membrane, segments keeled, narrowly perforate, cilia in groups of 1-4, nodulose to appendiculate. Spores spherical, finely papillose, 9-13(-21) µm diam. Calyptrae cucullate, naked, smooth.

  • Discussion

    1. Leptodictyum riparium (Hedw.) Wamst., Krypt.-Fl. Brandenburg 2: 878. 1906; Hypnum riparium Hedw., Sp. Musc. Frond. 241. 1801; Amblystegium riparium (Hedw.) Schimp. in Bruch, Schimp. & W. Gümbel, Bryol. Eur. 6(fasc. 55-56, Monogr. 1): 58. 1853; Stereodon riparius (Hedw.) Mitt., J. Linn. Soc., Bot. 8: 43. 1864; Chrysohypnum riparium (Hedw.) Loeske, Moosfl. Harz. 301. 1903, comb, inval. Plate 82, figures 1-6 Amblystegium riparium var. floridanum Renauld & Car-dot, Rev. Bryol. 15: 72. 1888; Amblystegium floridanum (Renauld & Cardot) Renauld & Cardot, Rev. Bryol. 20: 24. 1893. Amblystegium octodiceroides Müll. Hal., Hedwigia 37: 265. 1898; Leptodictyum octodiceroides (Müll. Hal.) Broth, in Engl., Nat. Pflanzenfam., ed. 2, 11: 337. 1925. Discussion. Leptodictyum riparium is characterized by plants with slender costae extending about 2/3 the leaf length, relatively long upper cells, and a large area of lax, broad cells near the insertion, especially juxtacostally. In its typical expression the leaves are wide-spreading, distantly placed, and soft. However, the plants are subject to environmental modification. When growing emergent (usually from standing water), the leaves are often erect rather than wide-spreading. When the plants are in highly calcareous, low-light situations, they are often much more diminutive in stature but otherwise identical in structure, i.e., the so-called var. floridanum. Our only Bahamian specimen (Britton 6464, NY) is just such a plant, and it was collected in a cave.

  • Distribution

    Range. Southern Canada, United States, Mexico, Guatemala, Europe, northern and southern Africa, northern and central Asia, Japan, Australia; Bahamas (Eleuthera), Cuba, Jamaica, Hispaniola (Haiti and Dominican Republic); growing on decaying vegetation, soil or sometimes rocks, often submerged or emergent, from near sea level to ca. 2000 m.

    Canada North America| United States of America North America| Mexico North America| Guatemala Central America| Europe| Africa| Japan Asia| Australia Oceania| Bahamas South America| Cuba South America| Jamaica South America| Haiti South America| Dominican Republic South America|