7. Pleuridium Rabenh., Deutschl. Krypt.-Fl. 2(3): 79. 1848.
Plants minute to small, yellowish green, gregarious or in loose tufts. Stems erect, simple or sometimes branched; central strand present. Leaves often erect or subsecund at the tips, not crispate when dry, small, distant at the lower stems, larger and crowded near the stem apex, lanceolate, gradually tapered from a narrowly ovate base to a slender, setaceous acumen, or sometimes subulate from a broad base; margins plane, entire below, serrulate above; costa single, strong, excurrent, often filling most of the subula; upper cells rhomboidal or rectangular, thin-walled, smooth; basal cells rectangular, thin-walled; alar cells not differentiated. Autoicous or rarely dioicous. Setae very short, straight; capsules usually immersed, subglobose to ovoid, rarely cylindric, bluntly mucronate to apiculate or sometimes rostrate; opercula and annuli not differentiated; stomata present; peristome absent. Calyptrae cucullate, covering the upper part of the capsules, rarely mitrate, smooth. Spores spherical, small, numerous, papillose.
There are about 30 species of Pleuridium in the world. Most of the species in the genus are distributed in the temperate regions. One species is known from China. The species most easily confused with Pleuridium is Eccremidium brisbanicum (Broth.) Stone & Scott, which was recently reported from Hong Kong (L. Zhang et al. 1998). However, we could not confirm this report.