Hygrohypnum alpinum

   Plants to 30 mm long, in somewhat glossy, olive-green to green mats usually with a russet wash in exposed areas. Stems weak, green when young, turning brown to red-brown with age. Plants prostrate to decumbent, irregularly branched with little differentiation of stems and branches. Leaves broadly ovate to almost orbicular with bluntly rounded apices, to 1.2 mm long, not at all falcate, diverging from stem at more than a 45 degree angle when wet or dry. Margins plane and entire below but prorate-serrate in the distal 1/2, shortly recurved into the decurrency at the base. Median laminal cells of well-developed leaves linear-vermiculose, 6–10: 1, to 6 µm broad, smooth, rather thick-walled with lumen: wall ratio 3–5: 1. Cells of alar region short rectangular and inflated, to 18 µm wide, 2–4: 1, thin-walled in a group extending up the leaf about 4 cells and extending interiorly about the same. Marginal cells, especially in proximal half of leaf, broader and more pellucid than adjacent interior cells. Cells in a large group at leaf apex prorate, short rectangular 2–5: 1, thick-walled with lumen: wall ratio mostly less than 1: 1. Costa mostly rather inconspicuous, only 4–6 cells wide at base, forked from near the base, with both forks ending below the leaf middle. Pseudoparaphyllia broadly ovate and rounded at apex, closely folded over bud, to 300 µm long. Axillary hairs 6–8-celled, of uniform diameter throughout, thin-walled, to 400 µm long, with two of the basal cells short but concolorous, not offset from leaf insertion. Stem cross-section with a stereome 2–4 cells thick with those thick-walled cells abruptly demarcated from an inner medulla of thin-walled and larger hyaline cells with central strand usually present but indistinct. Rhizoids scarse even on the older prostrate axes, fasciculate at abaxial leaf insertions, to 12 µm at insertion, red-brown, sparingly branched, smooth.

   Autoicous. Perichaetia placed on older prostrate stems with the outer bracts short and squarrose but with the inner bracts to 3 mm long, erect and closely sheathing the base of the seta. Inner perichaetial bracts prorate dorsally near the apex, ecostate to weakly costate, plicate, elliptic-lanceolate, mostly rather bleached brownish green, gradually contracted from base to the bluntly rounded apex with no alar differentiation and with margins entire below but serrate near apex. Seta to 15 mm long, smooth, erect, pale-brown. Urn pale-brown, to 2 mm long, about 2: 1, oblong-cylindrical, curved and inclined, not sulcate but lightly strangulate. Exothecial cells moderately thick-walled, not collenchymatous, in somewhat regular rows, to 20 µm broad, mostly rounded isodiametric to short rectangular, regular in size and shape, not strongly differentiated near the mouth. Stomata few, short and vertical pored, on lower portion of urn. Operculum conic-apiculate, to 1/5 as long as urn. Annulus present, not revoluble. Calyptra cucullate and smooth, sheathing only distal half of capsule. Exostome teeth inserted and somewhat united below the mouth of urn, to 400 µm long, lanceolate but with a prominent shoulder at about middle, transversely striate, inflexed when dry, yellow to orange, with a well defined zig-zag median commisural line. Endostome segments papillose, nearly as long as exostome, consisting of keeled, narrow segments with 1–2 cilia, arising from a basal membrane about 1/2 as long as exostome. Spores to 20 µm, obviously papillose.

Vouchers: Fresno Co.: between Golden Lake and Mono Pass, Sierra National Forest, Norris 47042 (determined by Jamieson); Mono Co.: Barney Lake, Toiyabe National Forest, Norris 67145; Siskiyou Co.: Duck Lake Creek at Forest Road 8, Klamath National Forest, Norris 23300 (determined by Jamieson).

Literature: Jamieson 1976.

Illustration References: Jamieson 1976.

Elevation by latitude plot for Hygrohypnum alpinum
   in California