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BFNA Title: Platydictya |
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AMBLYSTEGIACEAE
- PLATYDICTYA XX. PLATYDICTYA Berkeley, Handb. Brit. Mosses 145. 1863 * [Greek, platy, broad; dictyon,
net, alluding to pattern of leaf cells] Howard A Crum Lars Hedenäs Serpoleskea (Hampe)
Loeske Plants very small and slender, in light- to
dark-green or brownish mats. Stems
creeping, freely and irregularly branched, with a narrow central strand or
central strand absent, without a hyalodermis; paraphyllia absent; rhizoids or
rhizoid initials below or at abaxial leaf insertion, or axillary, smooth or
granular-papillose, slightly branched; axillary hairs with 1--2 distal
hyaline cells. Stem leaves
erect-appressed to loosely spreading, sometimes subsecund, lanceolate,
acuminate, not plicate, slightly concave, very small, 0.15--0.3(--0.5) mm;
marginal lamina cells 1-stratose, margins plane, entire to denticulate; costa
none or very short, double, and indistinct; median lamina cells subquadrate
to oblong-rhombic or short-rhomboidal, smooth; alar cells scarcely
differentiated to subquadrate, in small, inconspicuous groups, not decurrent.
Sexual condition autoicous or
dioicous. Inner perichaetial leaves
from sheathing base acuminate, smooth; margin entire to dentate; lamina cells
smooth. Capsule oblong-cylindric
to oblong-obovoid, erect and symmetric, or variously inclined and asymmetric;
peristome perfect or somewhat specialized; exostome margin entire or dentate
distally. Spores 8--13 \um, finely
papillose. Species 10 (4
in the flora): Europe, Asia, North America, Plants of Platydictya resemble Amblystegium but are even smaller and
have leaves virtually ecostate. The capsule is variously inclined and asymmetric
but not slenderly cylindric, curved-asymmetric, or greatly contracted below
the mouth and at the neck when dry. The genus, except P. jungermannioides (see below) belongs to the Amblystegiaceae
despite its ecostate, often secund leaves which suggest an alliance with the
Hypnaceae. L. S. Cheney's (1897) treatment of the genus Amblystegium, in a broad sense, is a useful reference for the
species of Platydictya.
Illustrations are presented in that work, as well as by H. A. Crum and L. E.
Anderson (1981). Platydictya confervoides and, P. subtilis, and P. minutissima should preferably be treated as a
separate genus, Serpoleskea in the
Amblystegiaceae. Platycictya
jungermannioides differs from the other three species in having purple
(rather than red-brown), granular-papillose (versus smooth), axillary
rhizoids (versus inserted below leaves), a narrow branching angle (versus
wide), and easily detached branches (versus firmly attached). These features
in fact fit better the Plagiotheciaceae than in the Amblystegiaceae. SELECTED
REFERENCES Crum, H. A. and L. E. Anderson. 1981. Mosses of 1. Rhizoids
axillary, at least when young purplish and granular-papillose; branching
angle narrow and branches easily detached . . . 1. Platydictya jungermannioides 1. Rhizoids
inserted at or just below costa, red-brown, smooth; branching angle wide and
branches more firmly attached. 2.
Leaf cells short throughout, 2--3:1 . . . . . 2.
Platydictya confervoides 2.
Leaf cells elongate, 3--6:1. 3.
Leaves entire; perichaetial leaves entire; capsule erect. . . . . 3. Platydictya subtilis 3.
Leaves serrulate; perichaetial leaves toothed; capsule suberect to
horizontal. . 4.
Leaves erect-spreading when dry, serrulate to the base; alar cells
subquadrate to short-oblong in small and inconspicuous groups; dioicous;
perichaetial leaves ciliate-dentate above; capsule suberect. . . . 3. Platydictya jungermannioides 4.
Leaves loosely spreading when dry, entire at base; alar cells scarcely
differentiated; autoicous; perichaetial leaves coarsely and irregularly
dentate above; capsule usually inclined to
horizontal. . . . . 4. Platydictya
minutissima 1. Platydictya jungermannioides (Bridel) H. A. Crum, Mich. Bot. 3: 60.
1864 Hypnum jungermannioides
Bridel, Musc. Recent. Suppl. 2: 255.1812; Amblystegiella
sprucei (Spruce) Loeske Plants in dense, soft, silky, green to
yellow-brown mats; pseudoparaphyllia none. Branching angle narrow, branches easily detached; rhizoids
axillary, at least when young purplish and granular-papillose. Leaves erect-spreading or sometimes +
secund, 1.17--1.3(--0.5) mm, not or somewhat narrowed to the insertion,
serrulate all around, especially at the insertion; distal cells 3--4:1,
shortly oblong-rhomboidal; alar cells subquadrate in small and inconspicuous
groups of 3--7 cells along the margins. Specialized
asexual reproduction by axillary obcuneate propagula. Sexual condition dioicous. Perichaetial leaves ciliate-dentate above. Seta 6--11 mm. Capsule
erect and symmetric or nearly so, 0.5--1 mm, oblong-cylindric, contracted
below the mouth and at the short neck when dry; annulus of 2 layers of cells;
operculum convex-conic, stoutly mammillate to + rostellate; stomata in
the neck; peristome teeth yellow; cilia of endostome 1--2, rudimentary to
well developed. Spores 11--13 µm. Rocks in damp,
sheltered places, crevices of cliffs or under rock ledges, peaty soil or
humus under overhanging turf, hollows under roots of trees, lower sides of
logs, perhaps limited to calcareous habitats; low to high elevations; Greenland; Alta., B. C., N. B., Nfld. and Labrador, N.W.T., N.S.,
Nun., Ont., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Iowa, Mich., Mont., N.Mex., N.Y., N.Dak., Vt., Wash., Wyo.;
Europe; Asia. Platydictya jungermannioides is easily recognized by its small size,
absent or almost absent leaf costa, easily detached branches, and its
axillary rhizoids that are purplish and granular papillose at least when
young. The branching and rhizoid characters differentiate this species from
the other three Platydictya species. 2. Platydictya confervoides (Bridel) H. A. Crum, Mich. Bot. 3: 60.
1964 Hypnum confervoides
Bridel, Musc. Recent. Suppl. 2: 153. 1812; Amblystegiella confervoides
(Bridel) Loeske; A. conferva Plants in dull, dark green to yellow-brown,
rather rigid mats; pseudoparaphyllia none. Branching angle wide, branches firmly attached; rhizoids below or
at abaxial leaf insertion, red-brown and smooth. Leaves erect-appressed or rarely subsecund when dry,
erect-spreading when moist, 0.15--0.3 mm, not much narrowed to the insertion,
entire or nearly so; distal cells 2--3(--4):1, oblong-rhombic; alar cells
subquadrate in small, inconspicuous groups of 3--6 cells, rarely more, at the
basal margins. Specialized asexual
reproduction absent. Sexual
condition autoicous. Perichaetial
leaves entire or obscurely serrulate distally. Seta 6--8 mm. Capsule inclined
to horizontal and asymmetric or rarely suberect, 0.8--1.2 mm, shortly
oblong-cylindric, contracted below the mouth when dry; annulus of 2 layers of
cells; operculum convex-conic, stoutly apiculate; stomata at base of the
capsule; peristome teeth yellow-brown; cilia of endostome in 2's and 3's. Spores 11--13 \um. Moist, shaded
limestone rocks, especially in stream valleys; low to moderate elevations; Nfld., N.S., Labrador, Ont., Que.,
Yukon; Alaska, Ala., Conn., Ill., Ind., Iowa, Kans., Md., Mich., Minn., Mo.,
N.J., N.Y., Ohio, Pa., S.Dak., Tenn., Vt., Va., Wis.; Europe; Asia
(Caucasus). Diagnostic
features of Platydictya confervoides include
the entire or obscurely serrulate leaf margins and short cells, as well as
its rupestral habitat. 3. Platydictya subtilis (Hedwig) H. A. Crum, Mich. Bot. 3: 60.
1964 Leskea subtilis
Hedwig, Sp. Musc. 221. 1801; Amblystegiella
subtilis (Hedwig) Loeske; Amblystegium subtile (Hedwig) Schimper; Serpoleskea
subtilis (Hedwig) Loeske Plants dull, in green to brownish mats; pseudoparaphyllia foliose. Branching angle wide, branches firmly
attached; rhizoids below or at abaxial leaf insertion, red-brown and smooth. Leaves erect-spreading and often
subsecund, 0.25--0.5 mm, somewhat narrowed to the insertion, entire or nearly
so; distal cells typically elongate, (2--)3--5:1, oblong-rhomboidal;
subquadrate alar cells rather numerous but inconspicuous, 6--8 or more along
the basal margins. Specialized asexual
reproduction absent. Sexual condition
autoicous. Perichaetial leaves entire. Seta 7--12 mm. Capsule
erect or nearly so, symmetric, 1--1.5 mm, oblong-cylindric, somewhat
contracted at the short neck and sometimes also below the mouth when dry;
annulus of 1 layer of cells; operculum conic, obliquely short-pointed to
rostellate; stomata in the neck; peristome teeth yellow- brown; cilia of
endostome 1--2 and rudimentary or lacking. Spores 9--13 \um. Bark at base
of hardwoods, exposed roots, rarely on logs; low to moderate elevations; N.B.,
N.S., Ont., P.E.I., Que., Yukon; Ariz.,
Ind., Maine., Mass., Mich., Mo., N.H., N.J., N.Y., N.C., Okla., Va., Vt.,
Wis.; Europe; Asia; South America. Particularly
distinctive features of Platydictya
subtilis include the entire leaf margins, elongate distal cells, and
fairly numerous subquadrate alar cells. The capsule is erect or nearly so.
This is the only species of the genus typically found on bark. 4. Platydictya
minutissima (Sullivant & Lesquereux) H. A. Crum, Bryologist 72:
244. 1969 Hypnum minutissimum Sullivant &
Lesquereux, Musci Bor.-Amer. 74. 1856; Amblystegiella
minutissima (Sullivant) Nichols; Platydictya jungermannioides var. minutissima
(Sullivant) H. A. Crum Plants very slender, in thin, + silky, green to brownish mats. Branching angle wide, branches firmly
attached; rhizoids below or at abaxial leaf insertion, red-brown and smooth. Leaves rather remote, loosely
spreading, 0.18--0.3 mm, narrowly lanceolate, gradually acuminate, not
narrowed to the insertion, serrulate nearly all around but entire at the
insertion; distal cells 3--6:1; alar cells scarcely differentiated. Specialized asexual reproduction
absent. Sexual condition
autoicous. Perichaetial leaves coarsely dentate distally. Seta 4--9 mm. Capsule small, 0.4--0.45 mm, suberect or, more commonly, inclined
or horizontal, broadly oblong-ovoid, asymmetric, without a neck, not
contracted below the mouth when dry; annulus of 1 row of cells; operculum
convex-conic, stoutly apiculate; stomata apparently none; peristome teeth yellowish;
cilia of endostome well developed, single or paired. Spores
8--13 \um. Rare; moist,
shaded rock (limestone and sandstone); low to moderate elevations; Que.; Platydictya
minutissima is rare,
and occurs in thin, rather silky mats.
The leaves are somewhat remote, loosely spreading when dry, and
serrulate except near the insertion; the leaf cells are elongate, and those
in the alar regions are scarcely differentiated. |
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