Lyellia R. Brown, Trans. Linn. Soc. 12: 561. 1819.
[For Sir Charles Lyell (1767--1849)]
Gary L. Smith Merrill
Plants robust, polytrichoid. Stems simple or rarely branched. Leaves with a sheathing base and divergent blade; sheath entire, hyaline-margined; limb firm, serrate-toothed in distal 1/2--1/3, with lamellae restricted to median portion of the limb, the lamina ± uniformly 2-stratose; lamellae entire, the marginal cells in section not differentiated, smooth. [Capsule ovoid, strongly dorsiventral, the upper surface flattened and concave with a narrow winged margin, lower surface rounded-convex, with hypophysis short, with conspicious stomata, guard cells surrounded by a circle of thin-walled, hyaline cells; operculum compressed- conic, with elongated oblique beak; peristome none; columella apex flattened and protruding from the central opening of a concave, thickened disc. Calyptra sparsely hairy to almost smooth. Spores echinulate.]
Species 4 (1 in the flora): Greenland, Arctic North America, e Asia (including Siberia).
Lyellia is a small genus with a disjunctive distribution, with representatives occurring in the Himalayas and eastward, and a single species, L. aspera, at high latitudes in Arctic America and eastern Asia. The capsules are strongly dorsiventral, resembling those of Dawsonia in shape, but lacking a peristome. The flattened columella apex projects from the center of the disc like a stopper in a wash basin (G. L. Smith, 1971, fig. 25); the epiphragm remains embedded in the operculum. The hypophysis has prominent stomata, the guard cells surrounded by a ring of thin-walled, hyaline subsidiary cells, which are sharply differentiated from the surrounding cells of the exothecium.
SELECTED REFERENCES
Smith, G. L. 1971. A conspectus of the genera of Polytrichaceae. Mem. New York Bot. Gard. 21(3): 1--83.
OTHER REFERENCES
Afonina, O. M. and E. N. Andrejeva. 1993. De sporogoniis Lyellia aspera (Hag. et C. Jens.) Frye. Novosti Sist. Nizsh. Rast. 29: 132--138.
Sharma, P. D. and R. S. Chopra. 1964. The life history of Lyellia crispa R. Br. Bryologist 67: 329--343.
Steere, W. C. 1956. The taxonomic status and geographic distribution of Philocrya aspera. Bryologist 59: 161--167
