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