1. Hookeria Smith, Trans. Linn. Soc. London. 9: 275, plate 23. 1808. • [For William Jackson Hooker, 1785-1865, British botanist and first Director of the Royal Botanic Gardens, Kew].
Plants dorsiventral, soft, flaccid, somewhat contorted when dry, whitish to light green or pale yellow. Stems 1-5(-7.5) cm, fleshy, succulent, sparsely and irregularly branched; cortical cells large, central strand distinct; paraphyllia absent; pseudoparaphyllia filamentous or absent; rhizoids few, on leaf apices, hyaline to brown, unbranched; axillary hairs hyaline, of 2-4 cells. Leaves ovate, oblong-ovate, elliptic, or broadly lanceolate, 2-4.5(-6) mm; base somewhat decurrent; laminal cells broadly oblong-hexagonal, oblong-rhomboidal, or short-rectangular, 100-200 (-250) µm, pellucid, walls thin, sometimes heteromorphic with smaller cell-pairs scattered throughout leaf; distal cells sometimes smaller; marginal cells elongate. Seta (0.8-)1-2(-2.5) cm, flexuose-curved, stout. Capsule oblong-cylindric or ellipsoid, 1.5-2 mm, neck short; exothecial cells subvesiculose; stomata in neck, phaneropore; annulus 1- or 2-seriate, weakly deciduous, cells large; operculum conic, long-rostrate; exostome teeth dark red, trabeculate, bordered, cross striolate basally, papillose distally; endostome pale, finely papillose, segments narrowly perforate on keel. Calyptra shortly conic-mitrate, 2-2.5 mm. Spores (10-)12-17 µm, smooth to scarcely or minutely papillose.
Species 2 (2 in the flora): North America, Mexico, West Indies, Central America, South America, Eurasia, Africa, Atlantic Islands, Pacific Islands.
Species of Hookeria are readily separated from other pleurocarpous mosses in the flora area by their absence of costa, complete lack of border, and very large laminal cells that are observable with a hand lens. When moistened, the plants appear almost transparent or pellucid. One species of Hookeria has a tropical distribution but also occurs in the temperate zone; the other is a north temperate species of both the New and Old Worlds.