BFNA Title: Hygroamblystegium
Author: Alain Vanderpoorten
Date: September 11, 2009
Edit Level: R
Version: 1

Bryophyte Flora of North America, Provisional Publication
Missouri Botanical Garden

BFNA Web site: http://www.mobot.org/plantscience/BFNA/bfnamenu.htm

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XX. Hygroamblystegium Loeske, Moosfl. Harz., 294. 1903 * [Greek hugros, moist, and genus Amblystegium]

Alain Vanderpoorten

Plants slender to robust, in dull, more or less stiff, yellow to dark green or blackish mats. Stem creeping, irregularly and often freely branched, without a hyalodermis; central strand present or absent; stem cortex of 2--4 layers of incrassate cells; paraphyllia often present; axillary hairs with a single brown basal cell and 1--2 elongate hyaline distal cells. Stem and branch leaves often differentiated, erect, not or slightly falcate-secund, oblong-lanceolate to oblong-ovate, gradually acuminate to an acute or obtuse apex; margin entire to denticulate, plane; costa single, broad, often curved beyond mid leaf, ceasing at mid leaf to excurrent; mid leaf cells smooth, firm-walled, eporose, becoming short-rectangular, broader, and often colored towards insertion; alar cells not or poorly differentiated, rectangular to quadrate, in rather indistinct ovate group along lower leaf margins. Sexual condition autoicous. Capsules inclined, arcuate, cylindric to oblong-cylindric, constricted below mouth when dry; exothecial cells long to short-rectangular, firm-walled, not collenchymatous, 30--105 x 18--35 \um; annulus of 2--4 rows of thin-walled separating cells; operculum acute to apiculate to rostrate; exostome teeth yellow-brown, bordered, on front surface cross-striolate basally, coarsely papillose distally, trabeculate at back; endostome with a high basal membrane, segments not or narrowly perforate, cilia in groups of 1--3, nodulose to appendiculate . Spores finely papillose.

 

Species: 1 (1 in the flora): bipolar distribution, including the Holarctic region, South America, South Africa, Pacific Islands (New Zealand), Antarctica.

 

Hygroamblystegium is a morphologically highly variable genus, and conflicting taxonomic treatments arose from different interpretation of character significance. The species of the genus are mostly aquatic to sub-aquatic and a substantial proportion of their morphological variation is purely plastic. None of the species form monophyletic groups in molecular phylogenetic analyses. All exhibit various ploidy levels and the group can be compared to complex of agamospermous vascular plants, where the wide range of genetic variability within “species” of polyphyletic origin are retained in the face of fast and independent evolution of polyploid genomes, unlikely to be associated with any kind of pattern of morphological variation. All species names previously recognized in the Flora region are considered here as synonyms of H. varium. Some traits are, however, indicative of habitat conditions. Although such plants with convergent morphologies do not form monophyletic lineages and should thus not be given species status, their recognition at an infra-specific level is supported ecologically. These infra-specific taxa correspond to terrestrial plants of wet meadows, fens, and marshes (var. humile), and strictly aquatic plants of oligotrophic, calcareous springs, which, owing to their endemic occurrence in North America, may be recognized at the subspecies level, namely subsp. noterophilum. Although some other expressions are extremely well-characterized, especially in fast-flowing water, in which plants often exhibit a robust, blackish, stiff, bristly habit because of persistent costae from which laminae have been eroded (H. tenax), plants previously described under epithets varium, fluviatile, and tenax form a continuous range of variation. The situation is especially complicated in North America since plants with a typical varium or tenax morphology often tend to develop an obtuse acumen (orthocladon expression) and therefore become almost impossible to distinguish from actual fluviatile.

Although phylogenetically unrelated, Hygroamblystegium sometimes bears strong resemblance with Cratoneuron filicinum (Hedw.) Spruce. The best example of this convergence has been called H. tenax var spinifolium (Schimp.) Jenn., a morphologically extremely well-characterized entity with a large size, long-excurrent, thick costa, which, despite the lack of inflated, hyaline alar cells and the strictly straight leaves, is an aquatic expression of Cratoneuron filicinum in oligotrophic, calcareous spring areas. Many weak forms of Cratoneuron with weakly developed, thick-walled and non-inflated alar cells are also often difficult to distinguish from Hygroamblystegium. Although the latter differs by its autoicous condition, some depauperate, sterile material may not be named with confidence.

 

SELECTED REFERENCES  Vanderpoorten, A. 2004. A simple taxonomic treatment for a complicated evolutionary story: the genus Hygroamblystegium. Monogr. Syst. Bot., Missouri Bot. Gard. 98: 320--327. Vanderpoorten, A. and A.-L. Jacquemart. 2004. Evolutionary mode, tempo, and phylogenetic association of continuous morphological traits in the aquatic moss genus Amblystegium. J. Evol. Biol. 17: 279--287. Vanderpoorten, A., A. J. Shaw and C. J. Cox. 2004. Evolution of multiple paralogous adenosine kinase genes in the moss genus Hygroamblystegium: phylogenetic implications. Mol. Phylog. Evol. 31: 505--516.

 

1. Hygroamblystegium varium (Hedwig) Mönkemeyer, Hedwigia 50: 275. 1911

 

Leskea varia Hedwig, Sp. Musc. Frond., 216. 1801; Amblystegium fluviatile (Hedwig) Schimper; A. noterophilum (Sullivant & Lesquereux ex Sullivant) Holzinger; A. varium (Hedwig) Lindberg; A. tenax (Hedwig) C. E. O. Jensen; A. humile (P. Beauvois) Crundwell; A. trichopodium (Schultz) Hartman; Hygroamblystegium fluviatile (Hedwig) Loeske; H. humile (P. Beauvois) Vanderpoorten, Hedenäs & Goffinet; H. noterophilum (Sullivant & Lesquereux) Warnstorf; H. tenax (Hedwig) C. E. O. Jensen

 

Stem leaves with rhombic to oblong-hexagonal, mid leaf cells, 10--60 x 5--15 \um, 2--7:1. Seta smooth, dark red, 12--22 mm. Spores 12--45 \um.

 

Wide ecological range, from sub-xeric habitats including rocks and tree trunks in hardwood mesic forests to marsh, fens, ponds, springs, and mountain fast-flowing streams; 0--2500 m; Alta., B.C., Man., N.W.T., N.B., Nfld., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., 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., Wash., W.Va., Wis., Wyo.; widespread in Holarctic: South America; s Africa; Pacific Islands (New Zealand); Antarctica.

 

1. Plants slender to moderately robust; costa less than 100 \um wide at base, ceasing at mid leaf to percurrent; lamina always 1-stratose . . . 1a. Hygroamblystegium varium subsp. varium

 

1. Extremely robust plants to 15 cm; costa strong, 110--140 \um wide at base, excurrent as a stout point; lamina sometimes 2-stratose in part, especially at the base near the costa . . . 1b. Hygroamblystegium varium subsp. noterophilum

 

1a. Hygroamblystegium varium (Hedwig) Mönkemeyer subsp. varium

 

Plants terrestrial, sub-aquatic or aquatic on rocks or wood, very rarely submerged and floating, yellowish to dark green. Stems stiff and rigid, to 10 cm but usually less; central strand usually present. Leaves ovate-lanceolate to ovate-triangular, 0.6--1.8 x 0.3--0.8 mm, margins entire or nearly so to serrate; costa ceasing at mid-leaf to percurrent or shortly excurrent; median cells 10--60 x 5--11 \um, 3--5:1; lamina 1-stratose.

 

Hygroamblystegium varium subsp. varium occurs in a wide range of habitats and displays, accordingly, a wide range of morphological variability. Many features, like the presence of a central strand in the stem, leaf shape, and shape of the leaf apex, are plastic and depend on water availability.

 

Wide ecological range, from sub-xeric habitats including rocks and tree trunks in hardwood mesic forests to marsh, fens, ponds, springs, and mountain fast-flowing streams; 0--2500 m: Alta., B.C., Man., N.W.T., N.B., Nfld., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., 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., Wash., W.Va., Wis., Wyo.; widespread in the Holarctic region: South America: s Africa; Pacific Islands (New Zealand); Antarctica.

 

1. Costa percurrent; alar cells usually somewhat differentiated, quadrate to short-rectangular, coloured; leaf shape and apex variable; plants never complanate . . . . 1a1. Hygroamblystegium varium var. varium

 

1. Costa ceasing before apex; alar cells undifferentiated; leaves broadly ovate, narrowed towards insertion; apex acuminate; plants sometimes complanate in habit  . . . 1a2. Hygroamblystegium varium var. humile

 

1a1. Hygroamblystegium varium subsp. varium var. varium

 

Stem leaves 0.6--2 mm; margins entire to denticulate; costa percurrent, 40--100 \um at base; apex obtuse to acute; median leaf cells 10--40 x 5--10 \um, 3—5:1; alar and basal cells somewhat differentiated, shorter, often coloured.

 

Hygroamblystegium varium subsp. varium var. varium is an exceedingly variable taxon occurring in a wide range of habitats. Leaf shape ranges from triangular with an apiculate apex to ovate-lanceolate with an obtuse apex. The latter morphology corresponds to what was previously called H. fluviatile. The continuous range of variation of leaf shape, the presence of leaves with different shapes and morphologies of leaf apices on the same stem, as well as the large plasticity of this character, however, precludes any formal recognition of the different morphotypes exhibited by the taxon.

 

Wide ecological range, from sub-xeric habitats including rocks and tree trunks in hardwood mesic forests to marsh, fens, ponds, and mountain fast-flowing streams; 0--2500 m; Alta., B.C., Man., N.W.T., N.B., Nfld., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Ala., 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., Wash., W.Va., Wis., Wyo.; widespread in Holarctic: South America; s Africa; Pacific Islands (New Zealand); Antarctica.

 

1a2. Hygroamblystegium varium subsp. varium var. humile Vanderpoorten & Hedenäs, J. Bryol. 31: xx. 2009

 

Stem leaves 1.2--1.9 mm, ovate-lanceolate; margins entire or minutely serrate; costa vanishing at mid-leaf to just before apex; median leaf cells 30--60 x 9--15 \um, 3--7:1; alar and basal cells shorter, rectangular, not sharply differentiated.

 

Hygroamblystegium varium subsp. varium var. humile is easily recognized by a much shorter costa than has been associated with other names included within H. varium, more elongate leaf cells, and undifferentiated alar cells. The length of the costa is, however, a plastic character that varies depending on water availability. In North America in particular, many specimens display a costa that ranges from ceasing at mid-leaf to sub-percurrent, rendering the distinction with other taxa within H. varium difficult. Variety humile often exhibits a complanate habit, which explains why the taxon has sometimes been associated with Leptodictyum, but this character also strongly varies and molecular data unambiguously show that the taxon is nested within Hygroamblystegium. Variety humile also bears strong resemblance with Pseudocampylium radicale, from which it is distinguished by non-decurrent leaves.

 

Wet meadows, fens, marshes; 0--3000 m; Alta., Man., N.B., Nfld., N.S., Ont., PEI, Que., Sask.; Ariz., Calif., Colo., Fla., Ga., Idaho, Ill., Ind. Iowa, Kans., Maine, Mass., Mich., Minn., Miss., Mo., Mont. N.Dak., N.J., N.Mex., N.Y., N.C., Nebr., Nev., Oreg., Pa., S.Dak., Tex., Utah, Vt., Wash., Wis., Wyo.; Central America; South America; Europe; Asia.

 

2. Hygroamblystegium varium (Hedw.) Mönkemeyer subsp. noterophilum Vanderpoorten & Hedenäs, J. Bryol. 31: xx. 2009

 

Plants often submerged and floating, dark green. Stems stiff and rigid, to 15 cm, with a central strand and several layers of thick-walled cortical cells. Leaves ovate-lanceolate to ovate-triangular, 1.2--2.4 x 0.3--1 mm; margins entire or nearly so; costa strong, excurrent, broad and thick at base, to 1/3 width of leaf base; median cells 20--45 x 6--10 \um; lamina sometimes 2-stratose in part, especially at base near costa.

 

Hygroamblystegium varium subsp. noterophilum is morphologically well-characterized by its large size, broad, excurrent costa ending into a stout point, and partly bistratose lamina. This taxon is restricted to areas of oligotrophic, calcareous springs. The leaves of submerged stems are, however, frequently quite different in shape from those of emergent stems and branches, suggesting that at least some of the morphological characteristics may be altered depending on water availability. Current phylogenetic analyses, in fact, failed to demonstrate the genetic integrity of the taxon. The morphology of populations from calcareous springs is typically very different from that of terrestrial or sub-aquatic populations in many bryophyte species (e.g., in Cratoneuron filicinum (Hedw.) Spruce, wherein such expressions are so different, that they were previously interpreted as a variety of Hygroamblystegium tenax, namely H. tenax var. spinifolium (Schimp.) Jenn.). Therefore, pending for additional evidence, noterophilum is treated here as a subspecies of H. varium.

 

Oligotrophic, calcareous spring areas; 0--2500 m; endemic to North America: B.C.; Ont.; Alaska, Ill., Mont., Minn., Iowa, Mich., Mo., Pa., S.Dak, Wis., Wyo.