4. Chryso-hypnum Hampe, Bot. Zeitung (Berlin). 28: 35. 1870. • [Greek chryseos, golden, and genus Hypnum].
William R. Buck
Mittenothamnium sect. Pseudomicrothamnium (Brotherus) Wijk & Margadant
Plants small or medium-sized, in soft, dense mats, pale to dark green, sometimes golden or brownish, dull. Stems creeping, freely and irregularly branched to regularly pinnate; hyalodermis absent, central strand present [or absent]; pseudoparaphyllia foliose. Stem and branch leaves similar, erect- to wide-spreading, , ovate to ovate-lanceolate or lanceolate, seldom plicate; base not or scarcely decurrent; margins plane to erect or recurved, often serrulate throughout; apex short- to long-acuminate; costa double, short; alar cells differentiated, quadrate to subquadrate; laminal cells prorulose at distal, sometimes proximal, ends abaxially, rarely smooth. Specialized asexual reproduction absent. Sexual condition autoicous [rarely dioicous]; perichaetial leaves erect, triangular-lanceolate, apex gradually long-acuminate. Seta reddish. Capsule horizontal to pendent, ovoid to short-cylindric, somewhat asymmetric, ± arcuate, often constricted below mouth when dry; annulus differentiated; operculum conic, usually apiculate; peristome double; exostome teeth with external surface cross striolate proximally, coarsely papillose distally; endostome basal membrane high, segments ca. as long as teeth, keeled, cilia in groups of 1 or 2. Calyptra naked or hairs few. Spores spheric, finely papillose.
Species ca. 12 (1 in the flora): se United States, Mexico, West Indies, Central America, South America, Asia, Africa.
Chryso-hypnum is here defined by prostrate, soft plants with ovate leaves and laminal cells that are prorulose at one or both ends. Other differences from Mittenothamnium Hennings, from which it was segregated, are the nonstipitate plants, the shorter capsules with apiculate opercula, and the usually hairy calyptrae. Subsequent work by N. Nishimura and H. Ando (1986) has verified the value of segregating Chryso-hypnum from Mittenothamnium.