Dense Fork Moss

Dicranum elongatum is easy to recognize because the plants are relatively small, slender, glossy, and grow in dense, compact tufts. The leaves are short, narrow, usually less than 6 × 0.5 mm, ending in a long, fine, tubulose subula, acute at the apex, smooth or nearly so on the abaxial surface, and have entire margins or rarely some denticulations at the apex. Capsules, which are not uncommon on plants in some arctic localities, are short, less than 2 mm, straight and erect to slightly arcuate, smooth but striate when dry.

Dicranum elongatum can readily be confused with the closely related D. groenlandicum. They both are arctic-alpine species sharing nearly the same type of habitat with almost the same distribution. They can usually be readily distinguished in their typical form but there appear to be many intergradations that cause difficulty. Dicranum groenlandicum has narrowly obtuse leaf apices and cells that are pitted to well above the middle of the leaf in contrast to the acute leaf apices and cells that are pitted only up to the middle of the leaf in D. elongatum. E. Hegewald (1972) found that the pits in the leaf are the most reliable means of separating difficult specimens of Finnish plants. H. A. Crum and L. E. Anderson (1981) expressed doubt as to whether the two are genetically different. Both D. elongatum and D. groenlandicum often bear at the apex of some stems julaceous shoots with small, ovate, broad leaves with obtuse apices. This can lead to the misidentification of some plants of D. elongatum unless the leaves in the basal part of the stems are always used to determine the shape of the leaf apices.

Plants slender, elongate, 6–16 cm long, yellowish green to brownish green above, dark brown below, shiny, in dense, compact tufts. Stems erect, simple or branched, usually with many branchlets, densely tomentose below. Leaves erect, scarcely altered or tips incurved-flexuose when dry, lanceolate, 3–5 mm × 0.4–0.5 mm, gradually narrowed from an ovate base to a subtubulose, acuminate acumen, the apex acute or obtuse; margins plane, entire below, slightly serrulate at the apex; costa stout, occupying 1/5 – ¼ the leaf base width, often percurrent or very shortly excurrent, smooth at back above; upper cells irregular, rounded quadrate or short- rectangular to slightly elongate, thick-walled, smooth, scarcely porose; basal cells elongate, strongly thick-walled, porose; alar cells quadrate or hexagonal, moderately inflated, yellowish brown, unistratose, not extending to the costa. Dioicous. Male plants normal. Setae single, straight, 8–15 mm long, yellowish; capsules erect to suberect, short-cylindric, 1.5–2.0 mm long, often slightly curved, furrowed when dry; opercula long-rostrate, nearly as long as the urns; annuli compound, in 1–2 rows of large, revoluble cells; peristome teeth 2–3 divided to the middle, reddish brown. Spores 18–22 µm in diameter, minutely papillose.

Plants in compact tufts, yellowish green to light green, glossy. Stems 2-10 cm, tomentose throughout with reddish brown rhizoids. Leaves erect-spreading, erect-appressed to rarely spreading when dry, apex sometimes flex-uose, smooth, (2.5-)3-4.5(-6) × 0.3-0.5 mm, from a lanceolate base to a long, fine, tubulose subula, apex usually acute, sometimes apical leaves of stems blunt, julaceous; margins entire, rarely slightly denticulate at apex; laminae 1-stratose; costa percurrent or shortly excurrent, ¹/6-¹/4 the width of the leaves at base, smooth or weakly rough above on abaxial surface, abaxial ridges absent, with a row of guide cells, two stereid bands not extending to apex, adaxial and abaxial epidermal layers of cells usually not differentiated or sometimes a few cells in both layers enlarged; cell walls between lamina cells slightly bulging; leaf cells smooth; alar cells 1-stratose or 2-stratose, well-differentiated, not extending to costa; proximal laminal cells usually elongate, pitted, (14-)24-36(-49) × (2-)4-6(-9) µm; distal laminal cells short-rectangular, quadrate, rounded, or sometimes irregularly shaped, incrassate, not pitted, (5-)12-17(-23) × (4-)6-8(-9) µm. Sexual condition dioicous; male plants as large as females; interior perichaetial leaves abruptly short-acuminate, convolute-sheathing. Seta 1.5-2 cm., solitary, yellowish to yellowish brown or reddish yellow. Capsule 1.2-1.8 mm, nearly straight and erect to slightly arcuate, striate when dry, yellowish brown; operculum 1.2-1.8 mm. Spores 17-22 µm.

Distribution: China, Japan, Russian Far East, Europe, and North America.

Habitat: on wet rocks or in apline tundra.

Dicranum elongatum Schleich.; Schwaegr. Suppl. I 1 : 171. 1811
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Dicranum subflagellare Card. & Ther. Proc. Wash. Acad. Sci. 4: 298. 1902.
Dioicous: male plants mingled with the fertile tufts, slender, elongate, with usually 2 or 3-' scattered flowers containing 3-5 antheridia and rather numerous paraphyses: fertile plants in compact, broad mats up to 15 cm. high, with slender stems tomentose to near the apex: stemleaves more or less erect-appressed or incurved when dry, the upper rarely somewhat curvedsecund, 3-4 mm. long, from a lanceolate base gradually narrowed to a subtubulose, acute point, entire above or serrulate on th e margin a nd sightly rough on^the^back ; costa a little above the base about one fourth the width^fthe leaf, per current or excurrent, in cross-section near the middle with 7 or 8 guide-cells and stereid-bands above and below of 2 or 3 rows of cells, the outer scarcely differentiated; alar cells golden-brown; cells of the lower part of the blade elongate, with thickened, pitt ed walls , the median and upper ones shorter, often scarcelyelongate, with thickened, not pitted walls ; inner perichaetial leaves about the length of the stem-leaves, rather abruptly narrowed "to a slender, entire point nearly as long as the broader part and mostly formed of the excurrent costa: seta 15-18 mm. long, slender, mostly palereddish: capsule about 1.5 mm. long, slightly nodding, curved, somewhat furrowed when dry, the exo thecal cells elongate with slightly sinuous, unequally thickened walls, with stoma ta in mostly 1 row near the base; annulus of 2 or 3 rows of cells; lid with the oblique beak about as long as the capsule; peristome-teeth dark-red, vertically striate to near the apex, divided two thirds down or more, with distinct articulations on the inner face about 20 p apart: spores roughish, up to 24 p in diameter.
Type locality: France.
Distribution: Greenland to Alaska and southward to the mountains of New England and Montana; also in Europe and Asia.