A Revision of Rigodium (Musci: Rigodiaceae)

Rigodium Kunze ex Schwaegr., a genus of tropical to austral-temperate pleurocarpous mosses, is comprised of six species and one variety. Prior to this study, 26 species were recognized, with five additional species generally accepted as belonging to other genera. Species of Rigodium, all dioicous, have wiry stems and branches, strongly dimorphic stem and branch leaves, extremely incrassate leaf cells that are prorulose to varying degrees (depending on the species), and hypnoid peristomes. The habit varies from arborescent with a well-developed stipe (e.g., R. toxarion) to more derived forms with either prolific (R. implexum) or reduced (R. pseudo-thuidium) branching. The genus has a disjunct distribution in Central and South America and southeastern Africa. The plants, usually epiphytic or terrestrial, generally grow in moist, montane forests. The center of diversity for the genus, where all six species occur, is in the Andean Cordillera along the Chilean-Argentinian border in central Chile. Observations on morphology, including those made with scanning electron microscopy (SEM), compose the basis of this revision, which includes computer-assisted analyses of phenetics (principal component analysis or "PCA" and canonical discriminant analysis) and cladistics (Phylogenetic Analysis Using Parsimony, PAUP). One previously undescribed species (R. adpressum) and one new combination at the varietal level (R. toxarion var. robustum) are presented. Rigodium is maintained within the monotypic Rigodiaceae, possibly most closely related to the Thuidiaceae.