Fissidens pauperculus

   Plants light green to rather deep green, to 6 mm high, with up to 10 pairs of leaves. Leaves, when dry, laterally twisted; when moist, spreading from stem at about a 30 degree angle, to 2 mm long, 3–4: 1 oblong to oblong lingulate. Vaginant lamina to 5:1, extending about 1/2 of leaf, the two sides converging at an acute angle, homostichous. Dorsal lamina mostly tapered to extinction above the leaf base, not decurrent. Median cells of apical and dorsal laminae unistratose, smooth, to 12 µm wide, thin-walled, hexagonal to rhomboidal with angular lumens and no corner thickenings. Median cells of vaginant lamina somewhat more regularly arranged, mostly a little longer than wide, 1–2:1, to 12 µm wide. Basal juxtacostal cells somewhat larger and more elongate. Costa to 25 µm at base, percurrent to subpercurrent, sometimes merging with limbidium at apex and forming an apiculus. Margin plane and entire throughout. Limbidium variably present, extending to apex or ending several cells below apex, occasionally almost absent from dorsal lamina. up to 4 cells wide, without stereids, not at all decurrent. Stem with no central strand and with a few thin-walled inner cortical cells abruptly differentiated from 1–2 layers of smaller, rather thick-walled outer corticals; lateral cells of outer cortex poorly differentiated. Axillary hyaline nodules not present.

   Dioicous or autoicous. Perichaetia terminal with seta to 8 mm, red-brown, nearly straight above the geniculate base, smooth. Urn to 0.8 mm long, oblong and symmetrical, about 2: 1. Operculum conic, about 1/3 as long as urn. Calyptra cucullate, smooth. Peristome reddish-brown, to 250 µm long, minutely papillose proximally, spirally ridged distally. Exothecial cells in regular vertical rows, somewhat bulging on outer surface, mostly isodiametric with angular lumens, rather thin-walled, to 15 µm wide. Spores to 20 µm, finely papillose.

Vouchers: Butte Co.: near Watson Ridge, Dillingham 779 (CAS) and tributary to Ponderosa Reservoir, 1.5 miles northwest of Fobestown, Dillingham 929 (CAS); Del Norte Co.: Stout Memorial Grove, Koch 3811 (UC); Humboldt Co.: James Irvine Trail, Prairie Creek Redwoods State Park, Jamieson 173 (UC), Arcata City Forest about 1 mile from Fickle Hill Road, Norris 68754 and Jolly Giant Creek about 0.5 mile east of Humboldt State University, Norris 85082a; Marin Co.: Mill Valley, Howe s.n. (UC ) and Dipsea Trail, Mt. Tamalpais State Park, Yurky 785 (SFSU); Mendocino Co.: Montgomery Creek Redwoods State Park, Kellman 2188 (CAS); Santa Cruz Co.: along Loma Prieta Grade Trail, Forest of Nisene Marks State Park, Kellman 2637 (CAS).

Literature: Holmberg 1969; Howe 1894; Jamieson 1969; Kellman 2003; Koch 1948, 1949a, 1950a, 1951d; Lawton 1971; Steere et al. 1954; Yurky 1990, 1995.

Illustration References: Malcolm et al. 2009 p. 87; Howe 1894; Lawton 1971.

Elevation by latitude plot for Fissidens pauperculus
   in California