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Isothecium myosuroides Bridel [Brachytheciaceae]
map of distribution

Bryol. Univ. 2: 369. 1827.
   Isothecium stoloniferum Brid., Bryol. Univ. 2: 371. 1827. -- Pseudisothecium stoloniferum (Brid.) Grout, Moss Fl. N. Amer. 3: 12. 1928
   Hypnum spiculiferum Mitt., J. Linn. Soc. Bot. 8: 34. 1864. -- Isothecium spiculiferum (Mitt.) Mac. & Kindb., Cat. Canad. Pl. 6: 204. 1892. --

Plants in cushions, mats or pendent streamers, olive-green to whitish-green, often with a russet cast. Stems to 10 cm long, ascending to erect; or pendent to 50 cm long. Pinnately branched and julaceous with branches of pendent plants microphyllous and attenuate, sometimes with the entire plant composed of such branchlets. Leaves to 3.5 mm, 4–7:1, symmetric, sagittate- to ovate-lanceolate, acuminate, often with the apex twisted, loosely imbricate when dry and little changed when moist. Margins plane but sometimes ascending in the acumen, not decurrent, entire to serrulate below the middle, coarsely serrate above. Median cells mostly smooth but usually with some dorsal prorations in distal portion of leaf, 5–12 µm wide, 6–10:1, moderately thick-walled with lumen/wall ratio to 2:1, usually pitted. Alar cells quadrate and very thick-walled (lumen/wall ratio 0.5–1:1), with intensely green contents, abruptly differentiated from adjacent laminal cells, often in an excavate pocket. Apical cells rhomboidal, nearly isodiametric. Costa extending about 3/4, usually ending in an abaxial spine.
    Pseudoparaphyllia deltoid to orbicular, strongly overarching the bud. Axillary hairs 5-celled, to 120 µm with 2 basal brown cells, not offset from leaf insertion. Rhizoids red-brown, 10–12 µm, smooth, in scattered fascicles on ventral portion of prostrate stem.
    Dioicous with male plants similar to females. Perigonia on main axis or on larger lateral branches. Perichaetia on main axis, to 2.5 mm. Perichaetial bracts ecostate, abruptly acuminate from a ligulate-lanceolate base, cells long vermicular, to 25:1. Seta to 2 cm long, exserted. Capsule brown, inclined to horizontal, not distorted or sulcate when dry. Urn to 2 mm, 2–3:1. Exothecial cells in regular vertical rows, to 25 µm wide, 1–2:1, with thick (lumen/wall ratio 4–6:1), red-brown walls, stomata restricted to neck. Operculum conic to short-rostrate, about 1/4 as long as urn. Exostome horizontally striate below, papillose above, yellow-brown. Endostome segments low papillose, open on keel, about as long as exostome with basal membrane about as high as the segments. Cilia 2, not appendiculate. Spores papillose, 15–20 µm.

This is one of the most variable mosses in California. At least four forms exist in the state -- forms which may very well be recognisable at the species level. In the humid coastal forest an only moderately julaceous, prostrate, green plant occurs on logs, soil and tree bases in more exposed sites. In this same coastal forest is a form which produces green, almost not at all julaceous prostrate stems on tree branches, and these stems produce large numbers of long and flagelliferous, pendent branchlets. In the interior forest, the dominant form of I. myosuroides is prostrate and very strongly julaceous; it never produces flagelliferous branchlets, and it has an olive green to russet cast. Some very moist forested valleys at high to moderate elevations in the Klamath Range have a form of Isothecium which is green to whitish green, without flagelliferous branches, but with an essentially erect stem. This latter plant has almost no proration of the laminal cells, and the marginal toothing is rather low. The type of I. myosuroides came from Europe, and our green plant of the coastal forests is very close to the European material, and to eastern North American material. Allen (1983) studied European and Eastern and Western North American specimens of this complex. His biometric comparisons of the populations led him to conclude that this variable group should be viewed as only a single species.
    All the forms of I. myosuroides share a single diagnostic feature -- the almost round (in surface view) patch of very green alar cells which typical form a somewhat concave pocket on each side of the base of the leaf.
   I. myosuroides has a rather peculiar distribution pattern in North America -- a pattern repeated by several additional mosses such as Antitrichia curtipendula. The primary range where it is quite abundant includes the humid Atlantic Coast of Northern Europe and also our west coastal North America. It is also sparingly found on similarly humid sites on the north shore of Lake Superior, on the Atlantic Coast from Maine to Newfoundland, and finally in the Southern Appalachians. Most botanists consider this a relictual distribution of a once more widely distributed humid north temperate forest.

Mail a correction to Paul Wilson ·
LiteratureAllen 1983; Holmberg 1969; Jamieson 1969; Kellman 2003; McGrew 1976; Shevock and Toren 2001; Smith 1970; Whittemore and Sommers 1999; Yurky 1995. As Hypnum myosuroides Brandegee 1891; Lesquereux 1868; Sullivant 1856; Watson 1880.
IllustrationsSmith 1978.
BioregionsCW, NW, SN.
VouchersSan Benito Co.: trail to the caves, Pinnacles National Monument, Koch 1325a (UC); Santa Cruz Co.: near Stevens Redwood Grove, Schofield 8328 (UC); Trinity Co.: East Fork road at Rich Gulch, north of Helena, Shasta-Trinity National Forest, Norris 18950; Tulare Co.: tributary of Squirrel Creek, Sequoia National Park, Norris, Shevock, & Barahona 87550.
   

Elevation by latitude plot for Isothecium myosuroides
   in California

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