2. Oligotrichum aligerum Mitten, J. Linn. Soc., Bot. 8: 48, plate 8. 1864.
Plants simple to sparingly branched by innovations, light olive green. Stems 2-3 cm, slender and wiry, erect. Leaves 3-5 mm, ovate-lanceolate, with a sub-sheathing base, ± erect-appressed when dry, somewhat spreading when moist, channeled distally, with lamellae on both surfaces; costa percurrent, ending in a short apiculus; margins narrowly reflexed, denticulate to distinctly serrate in distal 3/4; abaxial lamellae well-developed, on the back of both costa and lamina, the lamina with 3-4 regularly spaced lamellae on either side of the costa, 1-3 cells high, serrate like the leaf margins; adaxial lamellae 5-7, undulate, 5-9 cells high, confined to the midrib, undulate, serrate like the leaf margins; cells of leaf base short-rectangular; median cells of lamina rounded-quadrate, 12.5-20 µm wide, in ± regular longitudinal rows; perigonial leaves broadly triangular-ovate, forming a large, conspicuous rosette; perichaetial leaves larger and broader than the vegetative leaves, erect when dry, subsquarrose when moist. Seta 3-4 cm, reddish yellow, wiry, often strongly twisted in distal half when dry. Capsule 4-5 mm, cylindric, rather pale, terete or with 4 or more longitudinal ridges; hypophysis with numerous superficial stomata; peristome teeth 32, pale, double. Spores 10.5-13 µm.
Moist sandy or clay banks along roadsides, humus and upturned tree roots in rainforest; low to moderate elevations (50-1000 m); B.C.; Idaho, Mont., Oreg., Wash.; Mexico; Central America (Costa Rica); West Indies (Dominican Republic, Jamaica); Asia (Japan, China in Taiwan, Philippines).
Reports from mainland China and the Himalayas (Bhutan) require confirmation.
A North Pacific radiant species, Oligotrichum aligerum occurs on both sides of the north Pacific, extending southward to Central America and to Taiwan and the Philippines. The development of abaxial lamellae on the leaves in this species is striking and apparent, often even at low magnification.