1. Elodium (Sullivant) Austin, Musci Appalach. 52. 1870. • [Greek helos, marsh or marsh-meadow, and Latin -ium, diminutive, alluding to habitat].
Patricia M. Eckel
Hypnum sect. Elodium Sullivant in A. Gray, Manual ed. 2, 668. 1856; Helodium Warnstorf, name conserved
Plants medium-sized to large, green to yellow-brown. Stems erect or spreading, regularly ± 1-pinnate; paraphyllia filiform and narrowly lanceolate-foliose, branched or sometimes simple, cells long-rectangular, to 20:1, smooth, apical cell walls thin or somewhat thicker at tip; pseudoparaphyllia lanceolate-foliose, margins serrulate, proximal cells subquadrate, short- to long-rectangular, smooth. Stem leaves erect or erect-spreading, ovate-lanceolate to rounded-cordate; margins irregularly revolute proximally or strongly, broadly or narrowly revolute to apex, entire and minutely toothed near apex, or denticulate throughout; apex abruptly to gradually narrowed, acumen broad or slender; costa surface smooth or with 1 or 2 teeth near insertion; laminal cells with abaxial surface roughened, 1-papillose centrally over lumen or more often near distal ends, papillae small, delicate; medial cells elongate; apical cell 6-7:1, variously somewhat thickened distally, sometimes with one low papilla. Branch leaves similar. Sexual condition autoicous; perichaetial inner leaves with cilia absent. Seta 2-6 cm. Capsule with stomata present in neck. Spores (10-)11-15(-16) µm.
Species 3 (3 in the flora): North America, Eurasia.
Elodium is distinguished from species of Thuidiaceae by its 1-pinnate branches with narrowly tapering branch ends. The marginal laminal cells in the often twisted acumen of species of Elodium are shorter than the cells mid acumen and produce a smooth, short apical cell. The basal laminal cells are larger, laxer, and paler than the more distal cells; in Echinophyllum they are thick-walled and short-rectangular to (sub)quadrate and concolorous. The perichaetial leaves of Elodium are nearly smooth throughout and bordered by minute, uniform denticulations, or sharply, distantly and irregularly toothed from distal cell ends. In Echinophyllum, the margins are sparsely short-ciliate with hyaline, long-celled, narrow teeth composed of (one or) two elongate cells, free but parallel to the edge of the lamina. Both Elodium elodioides and E. paludosum seem intermediate in habitat preferences and able to tolerate seasonal desiccation.
SELECTED REFERENCES Abramova, A. L. and I. I. Abramov. 1972. On the span of the genus Helodium (Sull.) Warnst. J. Hattori Bot. Lab. 35: 371-381. Eckel, P. M. 2012. The genus Elodium (Bryophyta, Helodiaceae): A history and new combinations. Phytoneuron 2012-70: 1-7.