平藓科 ping xian ke
by Wu Peng-cheng
Plants small, medium-sized to rather robust, yellow to brownish green or grayish green, usually glossy, mostly complanate, in loose or compact mats. Primary stems creeping; secondary stems ascending, erect or pendulous, 1–3-pinnately branched or irregularly branched; stem in cross section rounded or oval, usually without a central strand, cortical layers composed of 3–4 layers of small, thick-walled cells and large, thin-walled inner cells. Stem and branch leaves similar or dimorphic (in the Neckeraceae, all description of stem leaves refer to secondary stem leaves), usually complanate, loosely appressed, rounded-ovate, oblong-ovate, ovate-lanceolate or lingulate, oblong-lingulate, mostly asymmetrical, plane or strongly undulate, rarely irregularly longitudinally plicate; leaf apices broadly acuminate, acute, apiculate, or rounded-obtuse to truncate; leaf bases plane, or incurved on one side or with a small lobe; margins usually serrulate to coarsely toothed above, rarely entire; costae single, slender to rather thick, sometimes double or forked, rarely absent; leaf cells mostly smooth, rarely unipapillose; upper cells usually shorter, often rounded-quadrate, rounded-polygonal, or rhombic, thick-walled; median and lower cells becoming elongate, from rhomboidal to linear, thinner-walled; basal juxtacostal cells often porose; alar cells not clearly differentiated; occasionally all cells uniform. Dioicous or autoicous. Setae very short to elongate; capsules immersed to submerged or long-exserted, subglobose, ovoid to cylindrical; opercula conic, shortly apiculate to long-rostrate; annuli not developed to well-developed; peristome double, sometimes reduced to rudimentary; exostome teeth lanceolate to linear-lanceolate, papillose or striolate at the base, rarely smooth, with low lamellae inside; endostome segments linear or linear-lanceolate, as long as the teeth or often shorter, reduced, smooth to papillose, sometimes keeled, perforate; basal membrane usually low or absent, sometimes high; cilia often absent, sometimes well-developed. Calyptrae cucullate or mitrate, smooth or somewhat hairy. Spores spherical, smooth or papillose.