Orthodontium pellucens (Hook.) B.S.G. in C. Mull.
Syn. 1: 240. 1849. -- Bryum pellucens Hook., Icon. Pl. 1: 34., 1836. Orthodontium gracile var. californica Howe, Erythea 5: 92. 1897.
Plants erect in green to pale green, rather glossy tufts, to 4 cm high. Leaves erect-spreading whether dry or wet, not significantly wrinkled, keeled. Leaves broadest above the base and gradually narrowed to the apex, narrowly lanceolate with rather broadly acute apices, to 4 mm long, less than 10: 1, not plicate. Median laminal cells rectangular with oblique end walls and with those walls rather thick (lumen: wall ratio about 4–6: 1) 6–9: 1, smooth, not or lightly pitted, to 15 µm wide. Leaf lamina unistratose throughout but markedly thicker near the costa compared with the margin. Basal and alar cells mostly yellowed, shorter and broader (to 30 µm broad) than median cells. Cells near leaf apex similar to median cells. Margins not decurrent, plane throughout, remotely serrulate to serrate but with a few scattered distal teeth formed from most of a single unreduced cell. Limbidium not well-differentiated but with more narrow cells, unistratose throughout. Costa cross-section elliptic, 1.2–1.5: 1, filling about 1/6 of leaf base, tapering above, green throughout, percurrent to weakly excurrent in the narrowly acute leaf apex. Costa cross-section 3 cells thick at mid-leaf, with much enlarged cells in the adaxial epidermis, without distinguishable guide cells, but with a small group of abaxial stereids. Axillary hairs to 4 cells long, to 150 µm, without basal brown cells, broad at base and attenuating distally. Macronemata deep red-brown, to 30 µm wide at insertion, smooth to very lightly papillose, sparingly branched, surrounding an isodiametric macronematal area to 100 µm wide. Micronemata to 15 µm wide at insertion, pale to hyaline, abundantly branched. Stem cross-section round, without a central strand, with the hyaline and leptodermous inner corticals abruptly transitting to a strongly enlarged hyaloderm. Gemmae occasional, appearing as fragmented distal portions of the larger, ascending rhizoids.
Autoicous. Perichaetial leaves somewhat smaller and more narrow than the adjacent vegetative leaves. Seta pale-brown, smooth, erect, to 5 mm long. Calyptra cucullate and smooth. Urn to 2 mm long, short cylindric, 2–2.5: 1, erect or slightly inclined, lightly or not at all sulcate, not strumose. Operculum short rostrate, to 1/5 of urn length. Suboral exothecial cells in 2–4 rows, to 12 µm broad, angular isodiametric and thick-walled with lumen: wall ration 2–3: 1. Exothecial cells at middle of urn rectangular, 3–5: 1, mostly with regularly thickened walls, not trigonous, to 40 µm broad, in somewhat regular rows, with lumen: wall ratio about 8: 1. Stomates phaneroporous, restricted to neck of capsule, almost as long as broad. Annulus not differentiated. Exostome teeth broadly separated one from another, pale to hyaline, to 300 µm long, narrowly linear, inconspicuously papillose, without median commissural line. Endostome with inconspicuous basal membrane. Segments smooth to lightly papillose, mostly somewhat longer than exostome, narrowly linear and not perforated or keeled. Cilia absent. Calyptra cucullate and smooth. Spores to 18 µm, smooth to very finely papillose.