BFNA Title: Platylomella
xxx. PLATYLOMELLA A. L. Andrews, Bryologist 53: 58. 1950 • diminutive of Platyloma, for limbate leaf margins
John A. Christy
Platyloma Kindberg; 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).
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.
1. Platylomella lescurii (Sullivant) Andrews, Bryologist 53: 58. 1950
Hypnum lescurii Sullivant in A. Gray, Man. Bot. N. U.S., ed. 2: 679. 1856; Amblystegium lescurii (Sullivant) C. F. Austin, Musc. Appal.: 62. 1870; Sciaromium lescurii (Sullivant) Brotherus in A. Engler and K. Prantl, Nat. Pflanzenfam. 1(3): 1030. 1908
Stems 1--6(--10) cm, matted with brownish rhizoids, often defoliate proximally, branches 1--2 cm, ascending and usually simple; paraphyllia becoming scarce in emergent plants. Stem leaves somewhat contorted when dry, 0.5--1.3(--1.5) mm; limbidia of 2(4) layers of cells, sometimes inconspicuous or disappearing before acumen or base, sometimes with spurs extending into the lamina; costa 40--60(--75) µm wide at base; distal laminal cells 6--12 x 15--20(--40) µm; basal cells with thick walls, sometimes pitted. Branch leaves similar to stem leaves, but slightly smaller and narrower. Perichaetial leaves 0.5--0.8 mm. Seta yellow to reddish brown, 10--30 mm. Capsule reddish-brown, 1.5--3 mm; exostome teeth yellowish-brown, cross-striolate proximally, papillose distally, trabeculate at back; endostome pale yellow, papillose. Calyptra yellow. Spores 12--17(--25) µm, yellowish-brown.
Capsules mature spring--early summer. Wet rocks, tree roots, rotting wood and bases of trees along streams, waterfalls and in seeps, submerged or in splash zone, in both lowland and montane deciduous or mixed deciduous-coniferous forest, both acid and calcareous rocks, widespread but often rare, sometimes locally abundant; 0--1500 m.; Ont., N.B., Nfld., N.S., Que., Ala., Ark., Conn., Del., Fla., Ga., Ill., Ind., Ky., La., Maine, Md., Mass., Mo., N.H., N.J., N.Y., N.C., Okla., Pa., S.C., Tenn., Tex., Vt., Va., W.Va (distribution after R. Ochyra 1987, supplemented by J. A. Christy).
The mostly bistratose margins, filiform paraphyllia, and saxicolous substrate in streams and seeps distinguish this taxon. It bears superficial resemblance to Amblystegium varium, Donrichardsia macroneuron, Hygroamblystegium noterophilum, Hygroamblystegium tenax and Platyhypnidium riparioides, but none of these have the limbidia characteristic of Platylomella. Sciaromium laxirete Abramova & I. I. Abramov, listed provisionally by R. Ochyra (1987) as a synonym of Platylomella lescurii, is known only as a Pliocene fossil from Bashkiria, western Eurasia.
OTHER REFERENCES 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 1: December, 2000
Version 2: January, 2001