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Nat. Pfl. 1(3): 1040. 1908. -- Hypnum molle (Hedw.) Loeske ssp. bestii Ren. & Bryhn, Bull. Ac. Int. Geogr. Bot. 10: 7. 1901. -- Hygrohypnum molle (Hedw.) Loeske ssp. bestii (Ren. & Bryhn) Grout, Check List Pleur. Moss. N. Amer. 16. 1929.

Plants to 100 mm long, in lustreless, olive-green to sordid-green mats usually with a russet wash in exposed areas. Stems rigid, green when young, turning almost black with age. Plants prostrate and irregularly branched with little differentiation of stems and branches. Branch axes prostrate to weakly decumbent, to 20 mm long. Leaves broadly ovate to almost orbicular with bluntly rounded apices, to 3 mm long, not at all falcate, diverging from stem at more than a 45 degree angle when wet or dry. Margins plane and entire but usually with light serrulations at the blunt apex. Median laminal cells of well-developed leaves linear-vermiculose, 6–10: 1, to 6 µm broad, smooth or with weak cuticular striations, thick-walled with lumen: wall ratio 2–3: 1. Cells of alar region quadrate to short rectangular in a small group similar in width to that of adjacent more distal cells but markedly smaller than the adjacent more interior rectangular cells. Marginal cells, especially in proximal half of leaf, broader and more pellucid than adjacent interior cells. Cells in a large group at leaf apex short rectangular 2–4: 1, thick-walled with lumen: wall ratio mostly less than 1: 1. Costa mostly forked from near the base, with both forks extending to near the leaf middle. Pseudoparaphyllia broadly ovate and rounded at apex, closely folded over bud, to 400 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 scarce even on the older prostrate axes, fasciculate at abaxial leaf insertions, to 12 µm at insertion, red-brown, sparingly branched, smooth.
    Dioicous. Perichaetia placed on older prostrate stems with the outer bracts short and squarrose but with the inner bracts to 2 mm long, erect and closely sheathing the base of the seta. Inner perichaetial bracts ecostate to weakly costate, plicate, narrowly lanceolate, mostly rather dark brownish green, gradually contracted from base to the bluntly rounded apex with no alar differentiation and with margins nearly entire. Seta to 20 mm long, smooth, erect, red-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, not in regular rows, to 20 µm broad, mostly rounded isodiametric but irregular in size and shape, not strongly differentiated near the mouth. Stomata few, short and vertical pored, on lower portion of urn. Operculum apiculate, to 1/4 as long as urn. Annulus present, not revoluble. Calyptra cucullate and smooth, sheathing only distal half of capsule. Exostome teeth inserted and somewhat united near mouth of urn, to 400 µm long, lanceolate but with a prominent shoulder at about middle, transversely striate, inflexed when dry, pale yellow to yellow, with a well defined zig-zag median commisural line. Endostome segments papillose, nearly as long as exostome, consisting of keeled, narrow segments with 2 cilia, arising from a basal membrane about 1/2 as long as exostome. Spores to 20 µm, finely papillose.

Elevation by latitude plot for Hygrohypnum bestii
   in California

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