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BFNA Title: Plagiobryum |
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Bryaceae – Plagiobryum XX. PLAGIOBRYUM Lindberg, Öfv. K. Vet.-Akad. Föhr. 19:
606. 1862 * [Greek plagio, oblique,
and bryon, a moss] Terry
A. J. Hedderson Plants
soft, slender, 0.3--2.5 cm, forming turf or in +/- caespitose clumps,
perennial, reddish brown to green or whitish- to silvery green with pink
tinges. Stems 0.3--1.5(--2) cm, highly branched proximal to the
apex by sterile innovations, in transverse section with 1--3 layers of
cortical cells that are smaller and thicker-walled than the interior cells, central strand present, red to
red-brown rhizoids usually abundant especially near base. Leaves
dimorphic, those of main shoot axes erect-spreading to appressed, larger
toward the stem apex, broadly ovate to lanceolate, usually slightly
decurrent, apices +/- reflexed, margins plane or recurved, entire, leaves of
innovations smaller, more ovate; costa present, single, sub-percurrent to
excurrent, in transverse section usually with a few abaxial stereids but
these occasionally absent; laminal cells 1-stratose, lax and
thin-walled throughout or in older leaves becoming firm-walled, rhombic to
rectangular distally, rectangular toward leaf base, toward margins usually
1--3 rows somewhat longer and narrower but not forming distinct border. Specialised asexual reproduction
absent. Sexual condition dioicous; perichaetia and perigonia terminal;
perichaetial leaves usually enlarged; perigonia bud-like with more ovate and
abruptly acuminate leaves. Seta slightly curved to cygneous,
often reflexed at base. Capsule horizontal to pendulous,
relatively large, clavate, gibbous, distinctly zygomorphic; neck
well-developed, 0.5--2.5 times length of urn, furrowed when dry; urn gibbous,
narrowed to an oblique mouth; annulus large, revoluble; operculum small,
mammillate to low-conic; peristome well developed with exostome shorter than
the endostome, teeth narrow-lanceolate, unbordered, yellowish to reddish
yellow; endostome loosely adherent to
exostome, processes narrow with narrow perforations, cilia rudimentary. Spores
adherent in tetrads, at least until maturity, elliptic, densely papillose,
yellow- to greenish brown or brown, 26--42 µm. Species 9 (2 in the flora): North America, Central
America, Europe, Asia, Africa, Pacific Islands (New Zealand). Plagiobryum
is easily distinguished when fruiting by the large, gibbous and distinctly
zygomorphic capsules. 1. Plants whitish to
silvery-green with pink tinges; innovations julaceous; leaves, especially of
innovations, imbricate and broadly ovate with plane margins; exostome only
slightly shorter than endostome; spores separate at maturity 1. Plagiobryum zierii 1.
Plants reddish brown; innovations not julaceous; leaves erect to
spreading, ovate-lanceolate to lanceolate, margins recurved; exostome
0.5--0.7 times height of endostome; spores dispersed in tetrads. …………………...
2. Plagiobryum demissum 1. Plagiobryum
zierii (Hedwig) Lindberg, Öfv. K. Vet.Akad. Förh. 19: 606. 1862 Bryum
zierii Hedwig, Spec. Musc. Frond., 182. 1801; Pohlia zierii (Hedwig) Schwägrichen Plants
0.8--2.5 cm, whitish or silvery green, usually with pink
tinges. Stems erect, 3--20 mm, soft, usually highly branched by elongate,
julaceous sub-perichaetial innovations.
Leaves of innovations
broadly ovate to nearly circular, concave, appressed or imbricate, slightly
decurrent, 0.7--1.3 x 0.4--0.8 mm, apices acute, ending in a small reflexed
point, margins plane, leaves on fertile shoots larger, more narrowly ovate;
costa ending in or shortly before leaf point, in transverse section
with 2--3 adaxial cells in a single layer, abaxial stereid band usually 2--3
cells thick but occasionally absent; laminal cells lax and thin-walled
distally, or in older leaves with +/- firm walls, rhomboidal or
elongate-rhomboidal, 2.5--5:1, 13--24 /um wide at mid-leaf, proximal cells
rectangular 2--4:1, firmer walled. Capsule horizontal to pendulous,
4--14 mm, neck 0.9--2.5 times length of urn, exostome yellow to yellow-brown,
distinctly papillose in lower 1/2, 0.85--0.9 times length of hyaline
endostome. Spores separate at maturity, 28-40 /um, brown to yellow-brown or
greenish brown, papillose. Capsules mature mid to late
summer or early autumn. Ledges,
crevices of moist or wet cliff faces, occasionally as scattered plants among
other bryophytes, often in the vicinity of waterfalls, most frequently found
on basic substrates including basalt, shale, limestone; 0--3,000 m;
Greenland; Alta., B.C., Nfld., N.W.T., N.S., Nunavut, Que., Yukon; Alaska,
Colo., Idaho, Mont., Oreg., Vt., Wash.; Central America (Guatemala), Europe,
Asia, Africa (South Africa). Plagiobryum
zierii is a predominantly montane-alpine species that is
disjunctively distributed between eastern and western North America. It
differs from P. demissum in
the julaceous, whitish or silvery green plants that are usually suffused with
tinges of pink. Plagiobryum demissum is
invariably red or reddish brown, and the shoots are non-terete. The broadly ovate, flat-margined leaves of P. zierii also serve to identify the
species. Sterile collections are more
likely to be confused with Bryum
argenteum, which is also silvery-green and has a similar leaf shape. However, plants of B. argenteum are smaller, have laminal cells firm to +/-
incrassate distally and quadrate proximally, lack pinkish colouration and
occur in drier, often disturbed or nitrogen enriched, habitats. 2. Plagiobryum demissum
(Hooker) Lindberg, Öfv. K. Vet.-Akad. Förh. 19: 606. 1862 Bryum
demissum Hooker, Musci Exotica 2: pl. 99. 1819; Meesia
demissa Hoppe & Hornschuch Plants
0.3--1.2 cm, red to reddish brown. Stems erect, 6--15 mm, soft, usually
branched by short sub-perichaetial innovations. Leaves
of innovations ovate-lanceolate to ovate, flat to slightly concave, erect to
erect-spreading, 0.9--1.4 mm x 0.25--0.5 mm, ending in a slender, acute apex,
margins recurved, on fertile shoots larger,
more distinctly lanceolate; costa ending in apex to distinctly excurrent, in
transverse section with 2--5 adaxial cells in one or two layers, abaxial
stereid band 2--4 cells thick; laminal cells +/- firm-walled distally,
narrowly hexagonal or rhomboidal to rectangular, 2.5--4.5:1, 12--20 /um wide
at mid-leaf, proximal cells thicker walled, 3--5:1. Capsule
pendulous, 2--5 mm, neck 0.5--1.2 times length of urn, exostome yellowish to
brown, nearly smooth to distinctly striate throughout, up to 0.5 times height
of hyaline endostome. Spores released in tetrads,
(26--)28--35(--42) /um, brown, strongly papillose. Capsules mature in late summer or autumn. Moist, often base
rich, cliffs, or on humusy soil in tundra; 0--4200 m; Greenland; Alta., B.C.,
Nfld., Nunavut, N.W.T, Yukon; Alaska, Colo.; Europe, Asia. Plagiobryum
demissum is a species of highly disjunctive distribution that is
almost always associated with mountainous areas. It is, surprisingly, little recorded from
most areas of the Canadian Arctic. The
species is easily recognised when fertile by the combination of reddish
gametophytes and pendulous, zygomorphic and distinctly “hump-backed”
capsules. When sterile the plants are
inconspicuous and practically indistinguishable from small reddish Bryum species. |
