Eucladium B. & S. in BSG, Bryol. Eur. 1: 93. 1846 (fasc. 33 36 Mon. 1).
Greek eu, well, very, true, good + klados, branch, twig, stem + ium, characteristic of; referring to the well developed whorls of stem leaves
P. M. Eckel
Plants small, in dense to deep tufts, turfs or swollen cushions, tufa forming, bright to dark blue green distally and pale green to yellowish brown proximally or sometimes throughout, rarely rufous; frequently bleached or whitened and indurated with encrusted lime. Stems slender, branching irregularly, densely foliate in whorls at successive innovations; transverse section rounded pentagonal with an irregularly inflated or enlarged hyalodermis and weakly developed sclerodermis; central strand absent; weakly radiculose, rarely strongly so; axillary hairs of 5- 10 cells, hyaline throughout; leaves appressed and scarcely incurved contorted when dry, erect spreading when moist, oblong to mostly linear lanceolate or linear subulate, base undifferentiated in shape to occasionally broadened oblong; margins plane, entire except for distinctive irregular hollow teeth on shoulder just distal to the base, not bordered; apex broadly to narrowly acute or subulate; costa strong, percurrent to shortly excurrent as a stout mucro, in transverse section elliptic; adaxial surface cells quadrate to elongate, adaxial epidermis present, adaxial stereid band, medial guide cells and abaxial stereid band present, abaxial epidermis sometimes absent, hydroid strand absent; basal cells sharply differentiated across to the margin where they become narrower, elongate, bulging rectangular to rhomboidal, hyaline, smooth, lax and thin walled; distal laminal cells subquadrate, walls sometimes irregularly thickened, papillae low, indistinct, simple or 2-fid, several per cell. Specialized asexual reproduction reportedly by rhizoidal brood bodies. Sexual condition dioicous; perigonia terminal, interior leaves long lanceolate, similar to those of the stem; perichaetia terminal, leaves as in stem leaves, ovate lanceolate, to 2.5 mm and sheathing. Seta single, erect. Capsule erect, symmetrical, yellow brown, ovoid to cylindrical; annulus weakly developed, of ca. 2 rows of subvesiculose cells; operculum obliquely conic rostrate; peristome teeth 16, straight or slightly oblique, lanceolate, finely papillose, entire to variously cleft. Calyptra cucullate, smooth. Spores spherical, mostly smooth. Laminal KOH color reaction yellow.
Species 1 (1 in the flora): U.S.A. to just north of the Canadian border; n Mexico; Central America; Europe; Asia; n and s Africa.
R. H. Zander (1993) removed Eucladium irroratum (Mitt. in Hook.) Jaeg. to the genus Tetracoscinodon, rendering Eucladium monotypic, characterized by absence of stem central strand and sclerodermis, a somewhat enlarged hyalodermis, costa broad in relation to the leaf, plane margins with their peculiar dentition at the leaf shoulder (a condition that may be variable or even rarely absent), and terminal inflorescences. The generic placement is near Trichostomum (R. H. Zander 1993). The genus is differentiated from other members of the former tribe Pleuroweisieae by the presence of a peristome, the distinctive serrulations on the proximal leaf margins, and the hyaline, thin walled and bulging rectangular differentiated basal cells (R. H. Zander 1977).
Crum, H. A. and L. E. Anderson. 1981. Mosses of Eastern North America 2 vols. New York. Osada, T. 1958. On the habitats of Eucladium verticillatum. Misc. Bryol. Lichenol. 15: 3. Saito, K. 1972. Gemmae formation on rhizoids of Eucladium verticillatum. Misc. Bryol. Lichenol. 6: 41- 42. Zander, R. H. 1993. Genera of the Pottiaceae: Mosses of Harsh Environments. Bull. Buffalo Soc. Nat. Sci. 32.
Zander, R. H. 1977. The Tribe Pleuroweisieae (Pottiaceae, Musci) in Middle America. Bryologist 80: 233 -269.