Fragile Leaf Dicranum Moss

Dicranum fragilifolium is a rare boreal species with shiny, light green to yellowish brown, erect-spreading leaves. The distal portion of the leaves is fragile and often broken off, thereby giving the plants a distinctive appearance. The deciduous leaf apices presumably serve as a type of asexual reproduction by regenerating to produce new plants. The species is often confused with D. tauricum, another species with deciduous leaf tips, but the latter occurs only in western North America. Where their ranges overlap they frequently are difficult to tell apart. When sporophytes are present the straight capsules of D. tauricum are distinctive from the usually arcuate ones of D. fragilifolium, which unfortunately rarely produces them. When sterile, the best way to separate the two is by the costa cross section in the proximal half of the leaf: D. fragilifolium has stereid cells in two thin bands while D. tauricum has none. Also, in D. fragilifolium there are 2-3 layers of cells above and below the guide cells, while in D. tauricum there are 1 or rarely 2 layers of cells. One other species with deciduous leaf tips that has sometimes been confused with D. fragilifolium is D. viride of eastern North America. It has a straight capsule like D. tauricum but as in D. fragilifolium capsules are rarely produced. The broad costa of D. viride, covering ¹/3 or more of the leaf base, will distinguish it from D. fragilifolium, the costa of which covers ¹/4 or less of the leaf base.

Plants in compact tufts, light green to yellowish brown, glossy. Stems 1.5-6 cm, densely tomentose with dark brown to red rhizoids. Leaves straight, erect-spreading, rigid, appressed when dry, smooth, (5-)6-7(-7.5) × 0.4-0.6 mm, most of the leaf tips deciduous and absent, concave proximally, canaliculate distally, from a lanceolate base to a long subula formed by the excurrent costa, apex acute; margins entire to somewhat serrulate above; laminae 1-stratose or some 2-stratose regions near costa; costa excurrent, ¹/4-¹/3 the width of the leaves at base, smooth or slightly rough above on abaxial surface, abaxial ridges absent, with a row of guide cells, two thin stereid bands (2-3 cells thick), adaxial and abaxial epidermal layers not differentiated or sometimes with a few cells in both layers enlarged; cell walls between lamina cells slightly bulging; leaf cells smooth; alar cells 1-stratose, sometimes with some 2-stratose regions, well-differentiated, sometimes extending to costa; proximal laminal cells elongate-rectangular, usually pitted or indistinctly pitted, (25-)39-55(-84) × (5-)7-8(-10) µm; median laminal cells rectangular, not pitted, (11-)21-22(-37) × (4-)7-8(-10) µm; distal laminal cells nearly elliptic, incrassate. Sexual condition dioicous; male plants as tall as females, usually more slender; interior perichaetial leaves abruptly long-acuminate, convolute-sheathing. Seta 1.5-2.5 cm, solitary, yellowish to brown. Capsule 1.8-2 mm, arcuate to nearly straight, ± erect, smooth, sometimes striate when dry, yellowish brown; operculum 1-2 mm. Spores 16-28 µm.

Plants small to medium-sized, 1–5 cm high, green to pale yellowish green, weakly shiny, in compact tufts. Stems slender, densely foliate, erect, simple or rarely branched, radiculose below. Leaves appressed, slightly altered when dry, erect-spreading or somewhat falcate-secund when moist, narrowly lanceolate, 6–7 mm long, gradually narrowed to a linear, often fragile, channeled subulate acumen; margins plane, entire below, subentire or minutely serrulate near the apex; costa occupying ca. ¼ the leaf base width, filling most of the subula, excurrent, ending in a long, smooth hairpoint, smooth at back above; upper cells irregular quadrate to short-rectangular, thick-walled, smooth; basal cells elongate, rounded linear-rectangular, thick-walled, porose; alar cells usually quadrate to short-rectangular, inflated, yellowish brown at the margins, hyaline next to the costa. Dioicous. Male plants dwarfed. Perichaetial leaves convolute-sheathing at base, abruptly subulate. Setae single, straight, 1–2 cm long, yellowish; capsules cylindric, up to 2 mm long, slightly curved, asymmetric, inclined, distinctly furrowed when dry; opercula conic-rostrate, nearly as long as the urns; annuli in 1–2 rows of large cells, often deciduous; peristome teeth lanceolate, vertically striolate below the middle. Spores ca. 24 µm in diameter, minutely papillose.

Distribution: China, Japan, Russia, Europe, and North America.

Habitat: on rotten wood, bases of trees, or wet rocks.

Orthodicranum fragilifolium (Lindb.) Podp., Consp. Musc. Eur. 152. 1954.

Dicranum fragilifolium Lindb, Oefv. Sv. Vet.-Akad
Forh. 14: 125. 1857.
Dioicous: malejrfants slender, up to 6 mm. high, growing, often 2 or 3 together, on tomentum of the upper fertile stems and bearing 1-3 flowers, each with 4 or 5 antheridia about 0.5 mm. long and few paraphyses, the perigonial leaves, mostly distinctly costate, from a brown base abruptly narrowed to a long, slender, more or less serrulate point: fertile plants in compact, mostly pale-green tufts, with slender stems up to 9 cm. high, tomentose to near the apex: stem-leaves erect-spreading, somewhat flexuous above, 6-7 mm. long, narrowly lanceolate and gradually long-subulate, from entire to more or less rough on the margin and back toward the apex, the fragile, often broken, nearly straight, grooved point mostly filled by the excurrent costa; costa one third to one fourth the width of the lower part of the leaf, in cross-section below showing 8-12 guide-cells with stereid-bands above and below, each of about two rows of cells of mostly uniform size ; alar cells brown to hyaline, extending to the costa 1 ; lower leafcells elongate with slightly thickened and pitted or not pitted walls, becoming shorter and not pitted above, the upper ones about 8 n wide and from nearly square to 2 or 3 times as long as broad; perichaetial leaves from a convolute base rather abruptly narrowed to a slender, smoothish point as long as the clasping part: seta 1.5 cm. long, finally reddish: capsule about 2 mm. long, oblong, curved, nodding, not strumose, furrowed when dry; annulus of mostly 2 rows of cells; lid conic-subulate, about as long as the capsule; peristome-teeth brown, vertically striate nearly to the apex, divided about one half down: spores rough, up to 25 ^ in diameter.
Type; locality: Sweden.
Distribution: Labrador to Alaska and southward to Minnesota, Montana, and' British Columbia, on logs; also in Europe and Asia.