RE-EVALUATION OF TORTELLA (MUSCI, POTTIACEAE) IN CONTERMINOUS U.S.A. AND CANADA WITH A TREATMENT OF THE EUROPEAN SPECIES TORTELLA NITIDA

Abstract

The moss genus Tortella (Pottiaceae) is re-examined for continental North America north of Mexico. Tortella alpicola is distinguished from T. fragilis as an uncommon but widespread taxon. Tortella japonica is considered to be a minor variant of T. humilis. Tortella rigens is new to the United States on the basis of comparison of American material with that of Europe, previous reports being erroneous. Tortella nitida is redescribed from authentic material and is excluded from the North American flora. The hitherto European Tortella tortuosa var. fragilifolia is reported from American plant populations. Tortella inclinata var. densa is reported as new to North America as a comb. nov. The bipolar distribution of Tortella fragilis is confirmed. Tortella inclinata var. inclinata is excluded from the flora of Arctic North America—specimens on which the species were cited were found to be T. inclinata var. densa instead. This study of the genus Tortella in continental North American north of Mexico was especially undertaken to address certain problematic taxa. An attempt was made to resolve past ambiguities by focusing on anatomical and morphological characters, for example to distinguish between the relatively common T. fragilis (Drumm.) Limpr. and a hitherto relatively unknown element in Tortella, T. alpicola Dix. Zander (1994d) added Tortella japonica (Besch.) Broth. to the Mexican flora, drawing attention to the relationship between the Japanese and Mexican floras. This created problems in separation of similar specimens with a broad distribution in Canada and the United States from the widespread northern hemisphere species T. humilis (Hedw.) Jenn. The decision that these two taxa are conspecific reveals greater variability in Tortella humilis than previously recognized, and