20. Platylomella A. L. Andrews, Bryologist. 53: 58. 1950. • [Genus name Platyloma and Latin -ella, diminutive, alluding to replaced later homonym].
John A. Christy
Platyloma Kindberg, Gen. Eur. N.-Amer. Bryin., 22. 1897, not Rafinesque 1833 [Brassicaceae]; Sciaromium sect. Platyloma Brotherus
Plants small to somewhat large, dark green to blackish with yellowish green shoot apices. Stems (fine, prostrate), irregularly branched or subpinnate; hyalodermis absent, central strand present; paraphyllia present, filiform; rhizoids basal or sometimes adventitious distally on decumbent shoots, forming tomentum, slightly branched, smooth; axillary hair distal cells 1 or 2, hyaline. Stem leaves erect-spreading, straight or incurved, cordate-ovate to ovate-lanceolate, not plicate, 0.5-1.5 mm; base not decurrent; margins plane, serrulate distally or to base, sometimes entire, limbidia conspicuous or sometimes inconspicuous, 2-4-stratose, cells incrassate; apex gradually or abruptly acuminate, sometimes apiculate, tips often obtuse; costa single, strong, percurrent to short-excurrent, usually confluent distally with limbidia; alar cells undifferentiated; basal laminal cells rectangular or oblong-hexagonal; distal cells short-rhomboidal to oblong-hexagonal, 6-12 × 15-40 µm. Branch leaves similar, slightly smaller and narrower. Sexual condition autoicous. Capsule horizontal to cernuous, oblong-cylindric, asymmetric, sometimes arcuate; peristome hypnoid; exostome margins dentate; endostome cilia appendiculate. Spores 12-17(-25) µm.
Species 1: c, e North America.
Platylomella has previously been included in Sciaromium (Mitten) Mitten, a synonym of Echinodium Juratzka (S. P. Churchill 1986).
SELECTED REFERENCES 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.