BFNA Title: Amblystegium
XX. Amblystegium Schimper, Bryol. Eur. 6: 45. 1853 * [Greek ambly, blunt, and stege, operculum, alluding to obtuse operculum]
Plants small and slender in soft mats, green to yellowish. Stems creeping, freely and irregularly branched; central strand of small, thin-walled cells present; hyalodermis absent; paraphyllia none; rhizoids or rhizoid initials only on stem or at abaxial costal insertion, smooth; axillary hairs with 1(--2) elongate hyaline distal cells. Stem leaves soft, erect to spreading but never complanate, ovate to oblong-lanceolate, acuminate, similar to branch leaves although somewhat larger, not plicate, slightly concave; marginal laminal cells 1-stratose; margin plane, entire or denticulate; costa 10--30 \um at base, mostly extending to about mid-leaf but sometimes shorter or reaching 3/4 of leaf length; median lamina cells firm-walled, slightly incrassate, eporose; alar cells often well differentiated, sub-quadrate to transversely elongate, in a broadly ovate or transversely triangular group along margin, reaching from leaf margin ca. 65% of distance to leaf mid point at insertion, not decurrent. Sexual condition autoicous. Inner perichaetial leaves narrowing from just before the acuminate apex, plicate. Capsule 1.5--2 mm, cylindric from a well-developed neck, strongly curved and inclined to horizontal; peristome perfect; exostome margin dentate or slightly so. Spores spherical, nearly smooth to minutely papillose.
Species 1 (1 in the flora): widespread in the Holarctic, reaching into subtropical and tropical areas.
Amblystegium differs from Hygroamblystegium by smaller plant size and a weaker costa, this less than 30 \um wide at base, most often ceasing at mid leaf. It rarely reaches 3/4 of leaf length but, in such cases, is straight and not curved as in Hygroamblystegium. Unlike the latter genus, Amblystegium lacks paraphyllia. So circumscribed, Amblystegium is a terrestrial genus that sometimes occurs in swampy but never aquatic or sub-aquatic habitats.
SELECTED REFERENCES Vanderpoorten A., B. Goffinet, L. Hedenäs, C. J. Cox, and A. J. Shaw. 2003. A taxonomic reassessment of the Vittiaceae (Hypnales, Bryopsida): evidence from phylogenetic analyses of combined chloroplast and nuclear sequence data. Pl. Syst. Evol. 241: 1--12.
1. Amblystegium serpens (Hedwig) Schimper, Bryol. Eur. 6: 53, pl. 564 (fasc. 55--56. Mon. 9, pl. 3). 1853
Hypnum serpens Hedwig, Sp. Musc. Frond., 268. 1801; Amblystegium juratzkanum Schimper; A. serpens var. juratzkanum (Schimper) Rau & Hervey
Stem leaves 0.5--1 mm; median lamina cells shortly oblong, 12--55 x 7-12 \um, 3--5:1. Seta elongate, 10--25 mm, reddish, smooth. Spores 9--18 \um.
Variable features in A. serpens include the serration of the leaf border, which ranges from entire to serrulate or even serrate; length of the costa, from very short (less than 1/5 of leaf length) to sub-percurrent; the sub-quadrate to transversely elongate shape of the alar cells; and leaf stance, which ranges from erect to spreading. These last two characters have sometimes been used to recognize a separate taxon, var. juratzkanum. The continuous range of variation of these characters, however, precludes any infraspecific division within A. serpens, which is, overall, a fairly-well circumscribed species with comparatively low levels of plasticity with regard to Hygroamblystegium species.
Tree trunks, rotten wood, rock, soil, in a range of habitats from (sometimes salty) swamps to rather xeric habitats; 0--3000 m; Greenland; Alta., B.C., Man., N.B., N.W.T., Nfld and Labr., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Ark., Calif., Colo., Conn., Del., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Mass., Md., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., W.Va., Wash., Wis., Wyo.; Mexico; Central America; South America; Europe; Asia; North Africa; Australia; Pacific Islands (New Zealand).