Mem. Cal. Acad. Sci. 1: 27. 1868. -- Polytrichum contortum Menz. ex Brid., J. f. Bot. 1800. 1(2): 287. 1801. Polytrichum laterale Brid., Musci Rec. Suppl. 1: 76. 1806. -- Pogonatum laterale (Brid.) Brid., Bryol. Univ. 2: 111. 1827.
Pogonatum erythrodontium Kindb. in Mac., Cat. Canad. Pl. 6: 150. 1892.
Plants in loose and mostly rather high turfs, to 20 cm high, unbranched or with innovations arising mostly below and lateral to the gametoecia. Leaves well-distributed along stem, lanceolate to linear lanceolate with an acute or bluntly acute apex, to 10 mm long, up to 8: 1 above the obovate and sheathing base which occupies 1/4–1/8 of leaf length, undulate when moist, strongly crispate when dry. Median laminal cells quadrate to somewhat transversely elongate with rounded lumens due to small corner thickenings, to 22 µm wide, markedly smaller toward the margins, smooth or with longitudinal cuticular ridges. Basal cells short rectangular, about 2: 1, not differentiated in alar region. Margin spinose dentate in distal 1/2–2/3; entire in region of sheath. Teeth of margin uni- to multicellular, often with a single red-brown terminal cell. Costa percurrent to subpercurrent, with 30–40 parallel photosynthetic lamellae on adaxial surface; lamellae, 2–5 cells high, nearly homogeneous in lateral view, occupying most of leaf at mid-point. Costa cross-section with two strongly developed stereid bands but with the adaxial band only about 1/2 as wide as the abaxial band, and with a two rather diffuse layers of guide cells. Axillary hairs to 800 µm long, uniformly hyaline throughout, inserted on each of the basal cells of each leaf. Rhizoids hyaline to pale brown, sparse to dense on lower portion of plant. Stem cross-section with very well defined central strand; with somewhat leptodermous inner cortical cells; and with 2–3 layers of red-brown, strongly pachydermous outer cortical cells.
Dioicous with male plants somewhat smaller than females. Perichaetia and perigonia terminal, forming prominent splash-cups. Monosetous with setae red brown, smooth, to 5 cm high, straight. Urn erect to somewhat inclined, oblong but flaring at mouth, to 2 mm long. Hypophysis not defined. Operculum rostrate, to 2/3 of urn length. Exothecial cells quadrate, to 20 µm broad, high mammillose with mammillae oriented toward the distal end of the cell and resembling prorae. Exothecial cells at capsule mouth dark red brown, very thick walled and transversely elongate in up to 8 rows. Stomates absent. Peristome to 200 µm long, from a basal membrane which comprises up to 1/4 of peristome length. Peristome teeth mostly 32, cellular, smooth, red brown throughout or with a narrow hyaline margin, irregularly inserted along mouth of urn, often paired. Calyptra cucullate, only sparsely hairy, sheathing all of the capsule. Spores smooth, to 12 µm in diameter.
When dry, the very crispate P. contortum can be confused only with Atrichum but the large number of photosynthetic lamellae and the lack of a differentiated limbidium should signal P. contortum. In its moist lowland habitats, only Polytrichastrum alpinum and Polytrichum commune share the feature of a dentate leaf with many photosynthetic lamellae. A field comparison of these plants shows P. contortum to have more remote foliation than the two above-named species, and its tendency toward crispation is shown by some twisting of its leaves even when they are fully hydrated.
P. contortum is one of a small number of California mosses with a distribution in a North Pacific arc which includes Canada, Alaska, far eastern Russia, China and Japan.
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