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XX. DICRANUM Hedwig, Spec. Musc. 126.
1801 * [Greek dicranon, pitchfork] Robert R. Ireland Plants in loose to dense tufts, yellowish
green to dark green, dull or shiny. Stems (0.5–)2–12(–18) cm, erect,
simple or forked, densely tomentose with white or reddish brown, smooth to
papillose rhizoids, these sometimes nearly lacking, rhizoids arising at bases
of branches (macronemata) and sometimes in rows scattered along stems
(micronemata). Leaves usually lanceolate, rarely ovate, proximal part concave,
rarely flat, distal subula keeled to tubulose, erect-appressed, erect-patent
or spreading, straight, weakly curled, crispate or cirrate when dry,
generally falcate-secund, less often straight, undulate, rugose or smooth,
margins plane to incurved or involute, entire to serrate in distal part,
entire proximally, apex acute to obtuse, tips sometimes deciduous, apparently
a means of asexual reproduction; laminae 1- or 2-stratose at margins or
sometimes near costa; costa single, ending before apex to excurrent, smooth
or toothed on abaxial surface, sometimes with 2–4 serrated ridges abaxially,
1–2 rows of guide cells, 2 well-developed stereid bands above and below,
sometimes slightly differentiated or lacking, extending to apex, or ending
before the apex, adaxial and (or) abaxial epidermal layers of cells
differentiated or undifferentiated, sometimes only a few cells in both layers
enlarged; laminal cell walls weakly to strongly bulging, or bulges lacking;
leaf cells pitted or nonpitted, smooth or sometimes abaxially, rarely
adaxially, mammillose, papillose or toothed by projecting cell ends, walls
often thickened; distal and median laminal cells short or long, quadrate,
rectangular or irregularly angled, proximal cells rectangular to linear, alar
cells inflated, 1- or 2-stratose, rarely more, generally orange to brown,
rarely poorly differentiated. Specialized asexual reproduction lacking
or as clusters of 1–6, deciduous, terete, flagelliform branchlets, borne in
axils of distal leaves. Sexual condition dioicous or
pseudomonoicous; male plants as large as female plants or dwarfed and
epiphytic on stem rhizoids of female plants; perigonial leaves ovate,
concave, short-acuminate; perichaetial leaves convolute-sheathing, abruptly
subulate or rarely interior leaves gradually acuminate. Seta
solitary or up to 6 per perichaetium, erect, twisted when dry, yellow, brown
or reddish, elongate, smooth. Capsule erect or inclined, straight
or arcuate, cylindric, smooth, striate or furrowed when dry, annulus of 1–3
rows of usually large, deciduous or persistent cells, sometimes indistinctly
differentiated; operculum long-rostrate, straight or arcuate; peristome
single, 16 teeth, split 1/3–1/2 their length into 2 or, rarely, 3 divisions,
vertically pitted-striolate proximally, papillose above, reddish brown. Spores
spheric, 12–30 µm, finely papillose. Calyptra fugacious, cucullate,
smooth, naked, covering most of capsule, Species ca. 140 (26 in the flora):
North America, Central America, South America, Europe, Asia, Africa, and
Australia. For this flora the segregate genus Orthodicranum is not recognized. Whether to recognize this genus or not has
been debated for years. W. Peterson
(1979) listed the following six characters that he considered important in
separating this segregate from Dicranum:
(1) capsules straight vs. capsules curved; (2) capsules smooth to slightly
wrinkled vs. capsules ribbed; (3) alar cells 1-stratose vs. alar cells
2-stratose; (4) peristome teeth relatively narrow (ca. 60 µm) vs. peristome
teeth relatively wide (70–95 µm or more); (5) specialized asexual
reproduction by broken leaf tips or flagellated branches common vs.
specialized asexual reproduction rare; (6) specialized habitat of rocks and
wood vs. habitat of wood or rock rare, usually on soil or humus. The species placed in Orthodicranum by him as well as by other bryologists are D. flagellare,
D. fulvum, D. montanum, D. tauricum and D. viride. Dicranum
fragilifolium is another species in
our flora that has been placed there by some bryologists (e.g., J. Podpera
1954). The problem with recognizing
the genus Orthodicranum is that some
of the members otherwise remaining in Dicranum
share one or more of the six character states Peterson outlined for the
segregate genus. Dicranum fragilifolium and D.
rhabdocarpa are two of the species
that commonly have some of the characters of Orthodicranum and some of those of Dicranum. Other species
in Dicranum less commonly have
characters of both genera. If for no
other reason but the sake of utility it is more practical at this time to
leave all the species in one genus so they can be keyed out together and
compared more readily. Perhaps when a
world monograph of the genus Dicranum
is done it will become more evident whether it is important to recognize Orthodicranum and perhaps even other
segregate genera. Leaf cross sections of the leaves employed
in this treatment are necessary to observe cell features of the costa and
laminal cells. The costa stereid and
guide cells, the adaxial and abaxial epidermal cells, the number of layers of
alar and laminal cells, and the bulges in the cell walls between the laminal
cells are all observable in cross section.
These characters are extremely important because they can reliably
differentiate many species of Dicranum. The leaf cross section characters are usually less variable and
less influenced by the environment than other gametophytic characters, such
as leaf habit, shape, margins and costa length characters, and are utilized
to a great extent since they are considered much more dependable in species
identification than some of the other characters in the genus. SELECTED REFERENCES Allen, B. 1998a. The genus Orthodicranum
(Musci: Dicranaceae) in Maine.
Evansia 15(1): 9–20. Allen, B.
1998b. The genus Dicranum
(Musci: Dicranaceae) in Maine. Evansia 15(2): 45–80. Bellolio-Trucco, G. and R. R.
Ireland. 1990. A taxonomic study of the moss genus Dicranum
(Dicranaceae) in Ontario and Quebec.
Canadian Journal of Botany 68(4): 867–909. Chien, G., D.H. Vitt and S. He. 1999. Dicranum.
Pp. 163–193. In G. Chien and M.R.
Crosby (Editors), Moss Flora of China, Vol. 1. Sphagnaceae-Leucobryaceae. Bejing, New York and St. Louis. Crum, H. A. and L. E. Anderson. 1981.
Mosses of Eastern North America.
Vol. 1. New York. Ireland,
R. R. 1971. Dicranum. In E.
Lawton, Moss Flora of the Pacific Northwest.
Pp. 72–81, pl. 29–33. The
Hattori Botanical Laboratory, Nichinan, Japan. Ireland, R. R.
1982. Moss Flora of the
Maritime Provinces. National Museums
of Canada , Nat. Mus. Nat. Sciences, Publs. in Botany, No. 13. Ottawa.
Nyholm, E. 1986. Illustrated flora of Nordic mosses. Fasc. I.
Fissidentaceae-Seligeriaceae.
Odense. Peterson, W. 1979.
A revision of the genera Dicranum and Orthodicranum
(Musci) in North America north of Mexico.
453 pp. Ph.D. thesis,
University of Alberta, Edmonton.
Williams, R. S. 1913. Dicranaceae. N. Amer. Flora 15(2):
77–166. 1. Leaves mostly straight, erect-spreading,
the tips deciduous and lacking. 2. Costa
lacking stereid bands, with 1–2 layers of cells above and below the guide
cells in the basal part of leaf; alar cells 1-stratose; capsule straight,
erect; w North America.......................... 2. Costa
with stereid bands, although sometimes weak, with 2–3 layers of cells above
and below the guide cells in the basal part of leaf; alar cells 1- or
2-stratose; capsule straight and erect or arcuate; w or more often e North
America. 3. Leaves
shiny, with proximal cells pitted, distal cells rectangular, alar cells
2-stratose or with a few 1-stratose regions, lamina rarely with 2-stratose
regions......................................... 3. Leaves
dull, with proximal cells not pitted (or with few pits), distal cells
quadrate, alar cells 1-stratose or with few 2-stratose regions, lamina often
with 2-stratose regions................ 23. Dicranum viride 1. Leaves rarely straight, usually crisped
or falcate, the tips mostly present. 4. Distal
leaf cells usually elongate, sinuose, pitted. 5. Costa
with 2 rows of guide cells, without abaxial ridges; leaves 10–15 mm; setae often
aggregate......................................................................................................... 6. Dicranum majus 5. Costa with 1 row of guide cells, often
with abaxial ridges; leaves often less than 10 mm; setae solitary or
aggregate. 6. Leaves keeled distally, margins strongly
serrate to toothed in distal 1/2; costa with 2–4 well-developed dentate
ridges on abaxial surface in distal part of leaf. 7. Leaves
spreading, strongly undulate; setae aggregate, 3–5 per perichaetium..... 1. Dicranum polysetum 7. Leaves falcate-secund, not or slightly
undulate; setae solitary, rarely 2 per perichaetium. 8. Interior
perichaetial leaves gradually acuminate; endemic to w NorthAmerica.............................................................................................. 3. Dicranum howellii 8. Interior
perichaetial leaves abruptly acuminate; throughout most of North America........................................................................... 2. Dicranum scoparium 6. Leaves tubulose to somewhat keeled
distally, margins entire to serrate in distal 1/2; costa without or with
poorly developed dentate ridges distally on abaxial surface. 9. Costa subpercurrent to percurrent; alar
cells usually 1-stratose, rarely 2-stratose inpart; capsule slightly arcuate
to straight and erect. 10. Leaves
spreading to slightly falcate-secund, margins serrate near apex; capsule 2–4
mm; endemic to w North America. 7. Dicranum rhabdocarpum 10. Leaves
erect-spreading to erect-appressed, margins entire; capsule 1.5–2 mm; across
n North America............................. 20. Dicranum groenlandicum 9. Costa subpercurrent to excurrent; alar
cells 2-stratose; capsule slightly to strongly arcuate. 11. Leaves
with a long, narrow subula, apex acute to somewhat obtuse............... 11. Leaves with a short subula, apex obtuse to
somewhat acute. 12. Leaves
usually with twisted apex when dry; portion of some stemsjulaceous and
composed of short, broad, concave, appressed, somewhat obtuse leaves;
proximal leaf margins ± involute......................................... 5. Dicranum leioneuron 12. Leaves
seldom or never with twisted apex when dry; without julaceous portions of
stems; proximal leaf margins flat. 13. Leaves
rugose-undulate, shiny, cells smooth on abaxial surface................... 4. Dicranum bonjeanii 13. Leaves
not or little rugose-undulate, dull, cells often somewhat rough on abaxial
surface.................................................... 2. Dicranum scoparium (form) 4. Distal
leaf cells usually short (quadrate, rectangular, or irregularly angled),
neither sinuose nor pitted (or with few pits). 14. Proximal
leaf cells not pitted (or with few pits); alar cells usually 1-stratose,
rarely 2-stratose; capsule generally straight; plants averaging 2–4 cm. 15. Leaf
lamina mostly 2-stratose above, costa usually more than 1/4 width of leaf
base; usually on rock, rarely on corticolous substrates......................... 22. Dicranum fulvum 15. Leaf
lamina 1-stratose above, costa less than 1/4 width of leaf base; common on
wood and humus, sometimes on soil or rock. 16. Plants
with 2–6 flagelliform branchlets (rigid and terete branches with appressed
leaves) in the distal leaf axils; brood branches lacking; leaves tubulose
distally and slightly papillose on abaxial surface, curled to crisped when
dry; distal leaf cells short-rectangular to quadrate.................................... 26. Dicranum flagellare 16. Plants
lacking flagelliform branchlets; usually with weak, slender, broodbranches
with linear, strongly crisped leaves when dry; leaves semi-keeled distally
and strongly papillose on abaxial surface, generally strongly cirrate when
dry; distal leaf cells regularly quadrate............................................... 25. Dicranum montanum 14. Proximal
leaf cells pitted; alar cells 1- or often 2-stratose; capsule generally
arcuate; plants averaging 3–8 cm. 17. Leaves
tubulose in distal 1/2; costa often indistinct and scarcely prominent on
abaxial surface. 18. Leaf
cells strongly papillose in distal 1/2 of leaf; costa without stereids in
distal 1/4–1/3 of leaf, adaxial and abaxial epidermal layer of cells not or
scarcely differentiated; capsule sometimes strumose, 1–3 per perichaetium;
endemic to nw North America............................................................ 16. Dicranum pallidisetum 18. Leaf
cells smooth or weakly papillose in distal 1/2 of leaf; costa with stereid
bands in distal part of leaf as well as proximally, adaxial and abaxial
epidermal layer of cells sometimes differentiated; capsule not strumose,
solitary; across North America. 19. Leaves
cirrate to crisped when dry; distal leaf cells short-rectangular to quadrate,
with thin walls, proximal cells 9–12 ìm wide; costa with adaxial epidermal
layer of cells enlarged (seen in cross section near leaf middle); capsule 2–4
mm.................................................... 18. Dicranum muehlenbeckii 19. Leaves
erect-appressed or slightly curled when dry; distal leaf cells elliptic to
rectangular, with thick walls, proximal cells 5–6 µm wide; costa with only a
few cells in adaxial epidermal layer enlarged; capsule 1–2 mm. 20. Proximal
leaves with acute apices; proximal leaf cells usually less than 40 μm, median
cells pitted mainly proximal to middle of leaf.................. 19.
Dicranum elongatum 20. Proximal
leaves often with blunt apices; proximal leaf cells usually morethan 40 µm,
median cells pitted well distal above middle of leaf.. 20. Dicranum
groenlandicum 17. Leaves
keeled in distal 1/2; costa prominent and rounded on abaxial surface. 21. Leaves
plane or indistinctly undulate near apex. 22. Leaves
strongly cirrate to crisped when dry, proximal cells usually less than 45 µm;
capsule 3–4 mm............................................. 13. Dicranum brevifolium 22. Leaves
straight to ± curled when dry, proximal cells usually more than 45 µm;
capsule 1–3 mm. 23. Leaves
with distal margins ± involute, laminae with few 2-stratoseregions on margins
in distal part; leaf cells smooth to slightly papillose on abaxial surface in
distal part of leaf 14. Dicranum acutifolium 23. Leaves
with distal margins erect, laminae with one or both distal margins
2-stratose; leaf cells papillose on abaxial surface in distal part of leaf..................................................................... 15. Dicranum fuscescens 21. Leaves
undulate or rugose (Dicranum condensatum indistinctly undulate). 24. Costa
ending well before apex, rarely nearly percurrent 8. Dicranum undulatum 24. Costa
percurrent to excurrent. 25. Leaves
erect-spreading to erect and compressed when moist; distal-median leaf cells
irregularly angled, with unequally thickened walls; capsule 1.5–2 mm,
slightly contracted below mouth. 26. Leaves
gradually narrowed to a long-acuminate apex; costa with a few differentiated
cells in adaxial epidermal layer, cell walls between lamina cells not
bulging; nw North America......................................... 26. Leaves
acute to gradually narrowed to a short-acuminate apex; costa lacking
differentiated cells in adaxial epidermal layer, cell wallsbetween lamina
cells weakly to strongly bulging; e North America. 27. Leaves
ovate to ovate-lanceolate, concave and arched, loosely imbricate when dry.................... 12. Dicranum spurium 27. Leaves
broadly lanceolate, not arched, slightly crisped when dry, not imbricate............................ 11. Dicranum condensatum 25. Leaves
falcate-secund when moist; distal-median leaf cells short- rectangular to
quadrate, with equally thickened walls; capsule 2–4 mm, not contracted below
mouth. 28. Leaf
margins strongly toothed distally, laminae with tooth-like projections
scattered distally on abaxial surface; setae often aggregate, 1–5 per
perichaetium; capsule not strumose.................. 9. Dicranum ontariense 28. Leaf
margins slightly serrate distally, laminae smooth to slightly rough distally
on abaxial surface; seta always solitary; capsule ± strumose. 29. Leaves
strongly crisped to cirrate when dry, proximal leaf cells usually less than
45 µm; stems densely tomentose................ 13. Dicranum brevifolium 29. Leaves
straight to curled when dry, proximal leaf cells often more than 45 µm; stems
somewhat tomentose 14. Dicranum acutifolium 1. Dicranum polysetum Swartz, Monthl. Rev. 34: 538. |