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BFNA Title: Hygroamblystegium |
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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, shortly decurrent. 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 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.; |