Plants green to yellow green, without reddish coloration, in mats or tufts, with prostrate complanate-foliate stems to 10 cm long and with erect spirally foliate gametoecial stems to 4 cm high. Leaves spreading when moist, crispate when dry, distant to approximate, to 8 mm long, elliptic to oblong-lanceolate, about 2: 1. Median juxtacostal cells to 75 µm wide, nearly isodiametric, smooth, gradually smaller toward the margins with juxtalimbidial cells only about 30 µm wide, isodiametric with angular lumens, with walls rather thick and pitted. Marginal cells differentiated into a strongly defined unistratose limbidium of linear cells. Basal and alar cells more elongate than median cells but not otherwise differentiated. Margins plane, denticulate near base, becoming dentate above with some of the teeth multicellular, decurrent in a several cell wide strip 2–4 mm long. Costa percurrent in the acute to short acuminate apex. Costa cross-section with ad- and abaxial cells stereidal to substereidal and with internal cells large and leptodermous except for a group of central cells which resemble a central strand. Axillary hairs to 5 cells long, to 150 µm, with one basal brown cell, not offset from leaf insertion. Rhizoids dense at base of gametoecial plant but seldom extending much above that base, smooth, red-brown, repeatedly branched, surrounding a macronematal area which is only 1.5–2 times as long as broad. Micronemata absent. Stem cross-section with a well-defined central strand, leptodermous inner corticals and several layers of strongly pachydermous, red brown outer cortical cells.
Dioicous with male plants somewhat smaller than females, bearing terminal perigonia. Perichaetia terminal with bracts somewhat smaller than vegetative leaves. Polysetous with up to 6 setae per perigynium. Setae yellow to yellow brown or red-brown, smooth, erect, to 4 cm long. Urn to 4 mm long, about 3: 1, yellow brown but dark brown near mouth, strongly inclined to pendent, not at all sulcate or strumose. Operculum conic. Annulus well-defined, revoluble. Exothecial cells near capsule mouth to 15 µm broad, isodiametric with rounded lumens in up to 4 rows. Exothecial cells at mid capsule hexagonal, to 15 µm broad, to 2: 1, with walls very thick (lumen: wall ratio 0.25–1: 1). Stomates primarily on neck, cryptoporous. Exostome pale yellow to sordid, to 600 µm long, undivided, finely papillose with papillae in close set horizontal rows. Endostome about as long as exostome with basal membrane comprising about 1/2 its length and with segments remotely papillose, open along keel and with 2–3, nodulose cilia. Calyptra cucullate, smooth. Spores to 25 µm, smooth or nearly so.
Plagiomnium insigne is endemic to western North America, and there its distribution closely follows that of the giant forests of the coast. Thus it reaches from Alaska to the central California coast and extends inland in the region of the Rocky Mountain -- Cascade convergence to Idaho, Montana and adjacent southern Canada.
This is one of the most conspicuous mosses on soil in the humid forests of northern California. In the redwood forests, this exceptionally large moss is especially common on flat soil on the banks of trails. In coastal forests near sea level P. insigne is the only likely member of the genus. At higher elevations, one looks for a very large and broad-leaved moss with a rather long and acute to acuminate apex and with margins denticulate to dentate nearly to the leaf base. Even with this combination of characters it can be confused with large specimens of P. medium (B.S.G.) T. Kop. In general the latter species is more likely to be in bogs or swamps while P. insigne will be on the litter of the forest floor. Handlens examination of the leaves is usually adequate to show the great differential between the size of its median cells relative to its marginal cells. P. medium has little such gradation in size and therefore the color from costa to margin will appear nearly constant under a handlens. P. medium is synoicous and its perichaetia usually have only 1–2 sporophytes; P. insigne is dioicous and its perichaetia almost always have more than 2 sporophytes.
|Literature||Koponen 1971; Lawton 1971; Spjut 1971; Yurky 1995. As Mnium insigne Bourell 1981; Holmberg 1969; Jamieson 1969; Kellman 2003; Koch 1950a; Koch and Ikenberry 1954; Lesquereux 1868; Smith 1970.|
|Illustrations||Malcolm et al. 2009 p. 183; Koponen 1971; Lawton 1971.|
|Bioregions||CW, NW, SN.|
|Vouchers||Del Norte Co.: Jedediah Smith Redwoods State Park, Norris 85080; Humboldt Co.: near Fish Lake above Weitchpec, Six Rivers National Forest, Norris 22225; Lake Co.: south of Summit Lake, Mendocino National Forest, Toren & Dearing 7210 (CAS) [determined by Wyatt]; Siskiyou Co.: road to Jackson Lake about 3.5 miles west of Callahan toward Cecilville, Klamath National Forest, Norris 22924; Tehama Co.; fork of Beegum Creek about 1.5 miles west of Rat Trap Gap, Shasta-Trinity National Forest, Norris 56987; Trinity Co.: Big Creek east of China Peak, Norris 76829 and East Fork Road at Rich Gulch north of Helena, Shasta-Trinity National Forest, Norris 18945; Tulare Co.: Deer Creek area south of Lion Ridge, Greenhorn Mountains, Sequoia National Forest, Shevock 10087.|
|keyimagelink(25%)||httpjpg caption: photo by Wilson of Coleman 511|