John A. Christy
Sciaromium sect. Platyloma Brotherus
Plants slender to somewhat coarse, prostrate, forming loose, dark green to blackish mats with yellowish-green shoot tips. Stems 1--10 cm, brownish-black, branching irregularly or subpinnately; pseudoparaphyllia foliose; paraphyllia filiform. Stem leaves smooth, erect spreading, cordate-ovate to ovate-lanceolate, gradually or abruptly acuminate, sometimes apiculate, tips often obtuse, 0.5--1.5 mm; margins plane, serrulate above or to the base, sometimes entire, with conspicuous limbidia of 2--4 layers of incrassate cells; costa single, strong, percurrent to shortly excurrent, usually confluent distally with limbidia; distal laminal cells short-rhomboidal to oblong-hexagonal, 6--12 x 15--40 µm, unistratose, smooth; basal cells rectangular or oblong-hexagonal, alar cells undifferentiated. Branch leaves similar to stem leaves, but slightly smaller and narrower. Sexual condition autoicous. Perichaetial leaves erect, lanceolate, acuminate, serrulate, costate. Seta single, straight or flexuose, often tortuose in aquatic plants, smooth. Capsule horizontal to cernuous, oblong-cylindric, asymmetric, sometimes arcuate, usually shrunken under the mouth when dry; exothecial cells rectangular; stomata superficial; annulus of 2--3 rows of cells, deciduous; operculum conic-apiculate; peristome hypnoid, exostome teeth 16, lanceolate; endostome with high basal membrane, cilia appendiculate. Calyptra cucullate, smooth. Spores 12--25 µm, finely papillose.
Species 1: e North America.
Platylomella has previously been included in Sciaromium (Mitten) Mitten, a synonym of Echinodium Juratzka (Churchill 1986).
Andrews, A. L. 1945. Taxonomic notes. IV. Sciaromium lescurii. Bryologist 48: 100--103. Ochyra, R. 1987. A revision of the moss genus Sciaromium (Mitt.) Mitt. III. The section Platyloma Broth. J. Hattori Bot. Lab. 63: 107--132.
Churchill, S. P. 1986. A revision of Echinodium Jur. (Echinodiaceae: Hypnobryales). J. Bryol. 14: 117--133. Crum, H. A. and L. E. Anderson. 1981. Mosses of Eastern North America. 2 vols. New York.
Version History for Platylomella:
Version 1: December, 2000
Version 2: January, 2001