Plants dark green to almost blackish, to 10 cm high, mostly with more than 20 pairs of leaves, little modified when dry. Leaves closely imbricated, spreading from stem at less than a 45 degree angle, to 5 mm long, oblong-lanceolate, about 4–5: 1, bluntly acute to rounded at apex. Vaginant lamina about 4:1, mostly extending 1/3 to 2/5 of leaf, with the two sides equal. Dorsal lamina rounded at base, not extending to insertion on stem. Median cells of all laminae in 2–4 layers, smooth on both surfaces, to 12 µm wide, irregularly hexagonal with angular lumens and thick walls with lumen/wall ratio 3–4: 1. Costa to 80 µm broad at base, tapering only near its apex, ending within about 5–10 cells of leaf apex. Margin mostly unistratose and plane, regularly crenulate. Costa cross-section of 4–6 layers of stereids, with guide cells rather poorly differentiated. Stem with central strand, thin-walled inner cortical cells and 2–4 layers of abruptly differentiated smaller, red-brown and thick-walled outer corticals, lateral cells of outer cortex somewhat differentiated. Axillary hyaline nodules not present.
Dioicous with sporophytes unknown in California (the description of the sporophyte is taken from Grout (1936). Perichaetia axillary in distal portions of female plants. Seta to 15 mm, erect. Urn to 1.2 mm long, oblong. Operculum conic-rostrate, to 1 mm long. Spores to 24 µm, nearly smooth.
This is a widely distributed aquatic to semiaquatic plant in temperate areas of Eurasia, and North and Central America. All the literature suggests that it is an obligate calciphile but many of the California localities are from rapidly flowing shallow water on serpentine. This is the only California Fissidens with such large and thick, almost black leaves.
|Literature||Barnes 1887; Bourell 1981; Crum and Anderson 1981; Flowers 1973; Frantz and Cordone 1967; Harthill et al. 1979; Holmberg 1969; Howe 1896; Kellman 2003; Kingman 1912; Koch 1950a, 1951e; Koch and Ikenberry 1954; Lawton 1971; Lesquereux 1868; Lesquereux and James 1884; Long 1978; Mishler 1978; Spjut 1971; Watson 1880; Yurky 1990, 1995.|
|Illustrations||Malcolm et al. 2009 p. 86; Crum and Anderson 1981; Flowers 1973; Iwatsuki and Suzuki 1982; Lawton 1971; Pursell and Allen 1994.|
|Bioregions||CaR, CW, NW, SN, SW.|
|Vouchers||Humboldt Co.: Shelter Cove, BLM Kings Range National Recreation Area, Norris & Piippo 82478; Los Angeles Co.: San Antonio Creek, Mt. Baldy Camp, Angeles National Forest, MacFadden 17156 (MO): Marin Co.: slopes of Mt. Tamalpais, Koch 2262 (UC); Monterey Co.: Big Sur River, Big Sur Redwood State Park, Koch 3643 (UC); Placer Co.: road to Bowman Lake about 2 miles north of Highway 20, Norris 77001; Plumas Co.: Highway 24 along North Fork Feather River, Plumas National Forest, Koch 1893 (UC); Siskiyou Co.: about 1.2 miles north of Cook and Green Pass, Rogue River National Forest, Shevock & Toren 20115; Tulare Co.: Dark Canyon along road to Jack Ranch near White River Campground, Sequoia National Forest, Shevock 14294 (confirmed by Pursell).|