Rhynchostegium serrulatum (Hedw.) A.Jaeger

  • Authority

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

  • Family

    Brachytheciaceae

  • Scientific Name

    Rhynchostegium serrulatum (Hedw.) A.Jaeger

  • Description

    Species Description - Plants medium-sized, in mostly lustrous, soft, bright- to yellow-green, often extensive, thin, loose to dense mats. Stems creeping, irregularly to subpinnately branched, the branches mostly <1 cm long; in cross-section with 2-3 rows of small thick-walled cells surrounding abruptly larger thin-walled cells, central strand small but distinct, of small thin-walled cells; pseudoparaphyllia foliose; axillary hairs with 1-2 short brown basal cells and 2-3 elongate hyaline to brown distal cells. Stem and branch leaves not differentiated, distant to close and ± overlapping, ± complanate dry or moist, wide-spreading, ovate-lanceolate to oblong-ovate, 1.4-1.9 mm long, gradually acuminate, the apex often with a single twist; margins serrulate throughout, more sharply and closely so above, plane to erect; costa single, slender, tapering distally, ending at ca. 3/4 the leaf length, usually projecting as a small spine; cells linear, straight to subflexuose, smooth, thin- to firm-walled, not porose, usually not becoming shorter in the acumen but in less acuminate forms the extreme apical cells somewhat shorter; alar cells scarcely differentiated, subquadrate to short-rectangular in a band across the insertion, becoming larger toward the costa. Asexual propagula none. Autoicous. Perichaetia inconspicuous; leaves erect, sometimes with somewhat spreading apices, oblong, ca. 2 mm long, ± abruptly long-acuminate; margins serrulate above, entire to crenulate below, plane; costa none or single and short, not extending into the acumen; cells linear, smooth, firm- to thick-walled, ± porose, becoming broader and rectangular toward the insertion; alar cells not differentiated. Setae elongate, smooth, reddish, 1.3-2.5(-3) cm long, ± flexuose, not or slightly twisted; capsules inclined, ± arcuate, asymmetric, especially in old capsules, short-cylindric, 1.5-2 mm long, constricted below the mouth when dry and empty; exothecial cells subquadrate to short-rectangular, firm-walled; annulus of 1-2(-3) rows of narrow, elongate, firm-walled cells; operculum obliquely short- to long-rostrate; exostome teeth reddish brown, triangular, obscurely shouldered, narrowly bordered, on the front surface cross-striolate below, densely papillose above, trabeculate at back; endostome finely papillose, often sparsely so, with a high basal membrane, segments keeled, broadly perforate, gaping with age, almost as long as the teeth, cilia usually in groups of 2-3, nodulose, shorter than the segments. Spores spherical, ± smooth, 11.5-16 µm diam. Calyptrae cucullate, naked, smooth.

  • Discussion

    2. Rhynchostegium serrulatum (Hedw.) A. Jaeger, Ber. Thatigk. St. Gallischen Naturwiss. Ges. 1876-77: 370. 1878; Hypnum serrulatum Hedw., Sp. Muse. Frond. 238. 1801; Eurhynchium serrulatum (Hedw.) Kindb., Ottawa Naturalist 7: 21. 1870; Brachythecium serrulatum (Hedw.) H. Rob., Bryologist 65: 125. 1962; Steerecleus serrulatus (Hedw.) H. Rob., Mem. New York Bot. Gard. 45: 681. 1987. Plate 98, figures 1-7 Hypnum frondicola Müll. Hal. ex Paris, Index Bryol. 642. 1896, nom. nud.; Rhynchostegium frondicola Müll. Hal., Hedwigia 37: 261. 1898; Rhynchostegium serrulatum var. frondicola (Müll. Hal.) Thér., Mem. Soc. Cub. Hist. Nat. “Felipe Poey” 15: 215. 1941. Discussion. Rhynchostegium serrulatum is recognized by its ± complanate foliation and ovate-lanceolate leaves serrulate almost throughout. Without doubt it is one of our most variable species, and it may represent a species complex. However, despite repeated attempts, I could not discern any clear-cut discontinuities of morphological variation. Aspect varies from plants with very distant leaves to ones with overlapping leaves. Leaves vary from relatively narrow with gradually or even sometimes ± abruptly acuminate apices, to ovate with short-acuminate apices. However, no correlation of the characters was perceived. Certainly the taxon could use more study over its entire range. The so-called var. frondicola is no more than a form with fairly distant leaves; similar expressions were studied from the United States. Robinson (1962: 125, 126) questioned the inclusion of R. serrulatum in Rhynchostegium, and included it in Brachythecium near B. rutabulum (Hedw.) Schimp. Later (Robinson, 1987) he placed it in Steerecleus. However, the species has a long-rostrate operculum unlike other Brachythecia. Similarly, R. serrulatum is complanate-foliate and not too unlike R. con-fertum, the type of Rhynchostegium. In the genera with rostrate opercula, the basal marginal laminal cells (at the insertion) are elongate rather than quadrate (fide K. McFarland, pers. comm.). Since this is also the case in R. serrulatum, I am quite comfortable with its placement in Rhynchostegium, preferring it to be accommodated there rather than in either Brachythecium or a segregate genus.

  • Distribution

    Range. Eastern North America, Mexico, Central America, northern Andean South America, Japan, Korea; Cuba, Jamaica, Hispaniola (Haiti and Dominican Republic), Puerto Rico; growing mostly on soil or thin soil over rocks or on humus, in mesic to humid forests or commonly in exposed habitats, at 100-1800 m.

    North America| Central America| Venezuela South America| Colombia South America| Ecuador South America| Peru South America| Japan Asia| North Korea Asia| South Korea Asia| Cuba South America| Jamaica South America| Haiti South America| Dominican Republic South America| Puerto Rico South America|