Helicodontium capillare (Hedw.) A.Jaeger

Authority

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

Family

Myriniaceae

Scientific Name

Helicodontium capillare (Hedw.) A.Jaeger

Description

Species Description - Plants small and slender, in dull, dark-green, mostly dense, ± flat mats. Stems creeping, to 2 cm long, freely branched, the branches mostly short, slender, terete-foliate when dry; in crosssection with 2-4 rows of small thick-walled cells surrounding larger thinner-walled cells, central strand usually present, small; pseudoparaphyllia foliose; axillary hairs with 1-2 short hyaline basal cells and a single somewhat elongate hyaline distal cell. Stem and branch leaves similar, crowded, appressed when dry, wide-spreading when moist, oblong-ovate-lanceolate to ovate, 0.6-1 mm long, bluntly acute to short-acuminate, somewhat concave, slightly decurrent; margins crenulate to serrulate above, more pronounced in longer acumina, entire below, plane; costa single, ending 2/3-3/4 or more the leaf length, the more acuminate leaves with costae ending lower, smooth or projecting as a small spine at apex; cells rhomboidal to long-hexagonal (in more acuminate leaves), smooth, firm-walled, becoming longer toward the insertion, especially juxtacostally; alar cells ± quadrate in 4-6 rows, not extending over the costa. Asexual propagula none. Autoicous. Perichaetial leaves sheathing, broadly oblong to oblong-ovate, 0.45-0.85 mm long, abruptly broadly acuminate, concave; margins serrulate above, subentire below, plane; costa single, ending ca. midleaf; cells long-hexagonal, ca. 6:1, smooth, firm-walled, becoming rectangular toward the insertion; alar cells gradually differentiated. Setae elongate, slender, usually somewhat roughened, especially near middle, occasionally smooth, reddish, 5-6 mm long; capsules erect, symmetric, ovoid to short-cylindric, ca. 1 mm long, dirty-yellow, often darkened near mouth, contracted below the mouth when dry and empty; exothecial cells short-rectangular, ± thick-walled, becoming smaller and thinner-walled in 1-3 rows at the mouth; annulus not differentiated; operculum obliquely blunt-rostrate, slightly longer than 1/2 the urn length; exostome teeth narrowly triangular, yellowish when young, becoming brownish gray with age, shouldered, bordered, on the front surface with a zig-zag median line, cross-striolate below, papillose above, trabeculate at back, usually unornamented; endostome with a moderately high, smooth basal membrane, segments papillose, keeled perforate, ca. as long as the teeth, cilia none. Spores spherical papillose, 15-20 µm diam. Calyptrae cucullate, naked, smooth.

Discussion

1. Helicodontium capillare (Hedw.) A. Jaeger, Ber. Thätigk. St. Gallischen Naturwiss. Ges. 1876-77: 225. 1878; Leskea capillaris Hedw., Sp. Musc. Frond. 221. 1801; Hypnum capillare (Hedw.) P. Beauv., Prodr. Aethéogam. 62. 1805, hom. illeg., non (Hedw.) F. Weber & D. Mohr, Index Mus. Pl. Crypt. 3. 1803 [= Bryum capillare Hedw.]. Plate 107, figures 1-6 Leskea minutula Brid., Musc. Recent. Suppl. 2: 69. 1812. Hypnum portoricense Balb. ex Brid., Bryol. Univ. 2: 301. 1827, nom. nud. in syn. Helicodontium tenuirostre Schwagr., Sp. Muse. Frond. Suppl. 3(2): 293. 1830; Hypnum tenuirostre (Schwagr.) Müll. Hal., Syn. Musc. Frond. 2: 411. 1851, horn, illeg., non Hook., Musci Exot. 2: 111. 1819 [= Sematophyllum uncinatum I. G. Stone & G. A. M. Scott]; Leskea tenuirostris (Schwägr.) Hook. ex Hampe, Vidensk. Meddel. Dansk Naturhist. Foren. Kjøbenhavn III, 9-10: 266. 1878, hom. illeg., non Bruch & Schimp. ex Sull. in A. Gray, Manual 668. 1848 [= Pylaisiadelpha tenuirostris (Sull.) W. R. Buck]. Hypnum exilissimum Sull., Proc. Amer. Acad. Arts 5: 286. 1861; Helicodontium exilissimum (Sull.) A. Jaeger, Ber. Thätigk. St. Gallischen Naturwiss. Ges. 1876-77: 225. 1878. Discussion. Helicodontium capillare is recognized by plants with mostly ovate leaves with a slender costa ending somewhat to well above midleaf and cells mostly 3-4:1. Plants of marginal habitats have narrower leaves, shorter costae, and relatively longer cells. The plants are frequently fertile and the capsules are erect, often with dark mouths. The species might be confused only with Austinia tenuinervis. However, in that species the plants are even smaller; the costa, although single, is weaker; and the peristome is of endostome only. Helicodontium capillare is one of the most common and weedy mosses in mesic, lowland forests (which are common in the Greater Antilles but mostly destroyed in the Lesser Antilles). Leaf shape, with consequent differences in degree of serrulation, costa length, and cell length, varies with habitat. These minor modifications have been described as species but do not seem worthy of taxonomic recognition. Plants of H. tenuirostre are relatively large, with broadly ovate leaves and bluntly acute apices. At the other end of the spectrum, H. exilissimum, described from Cuba, is a slender, depauperate plant with lanceolate, short-acuminate leaves. These differences appear to be environmentally induced, as evidenced by the presence of plants with leaves of one “species” on one branch and leaves of another “species” on another branch of the same stem. A variability in seta roughness does not correlate with leaf characters. Because H. capillare is so widespread in the American tropics, one would expect it to be pantropical, or at least to occur in lowland west tropical Africa.

Distribution

Range. Mexico to northern Argentina; Cuba, Jamaica, Hispaniola (Haiti and Dominican Republic), Puerto Rico, St. Martin, Saba, Nevis; most often growing on tree trunks but also on soil, rocks (frequently limestone), and logs, in fairly open, mesic forests, at 100-1000 m.

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