The Bryum bicolor Complex in North America

The Bryum bicolor complex includes four species in North America: B. bicolor, B. gemmilucens, B. gemmiferum, and B. barnesii. Bulbil morphology is the most important taxonoinic character for delineating the four North American species recognized, but care must be taken not to confuse them with morphologically similar restricted buds produced by, other Bryum species. Bryum bicolor is the only northern hemisphere species of the complex with bulbils single per leaf axil, bat is sometimes considered to be identical with the southern hemisphere species, B. dichotomum. After examination of the North American herbarium material and the types of B. bicolor and B. dichotomum, we could not perceive morphological differences between the two species. However, our survey did not include any other southern hemisphere specimens and we therefore kept the name B. bicolor pending for further studies on the variability of the species of the complex in the southern hemisphere. Bryum barnesii, B. gemmiferum, and B. gemmilucens all produce many bulbils per leaf axil but differ in bulbil color, shape. and size. Bryum gemmilucens is characterized by 100-200 mum long yellow, orange or red bulbils, B. barnesii by usually larger, 200-450 mum long greenish bulbils with broad, obtuse to largely acute primordia; and B. gemmiferum by 150-350 (450) mum long, yellow green, rarely brownish bulbils with tooth-like primordia. Leaf morphology is too variable to be used as a reliable taxonomic character within the complex. Costa length is quite variable, and plants exhibiting large bulbils and strongly excurrent costa approach B. dunense, considered to be a synonym of B. bicolor. Similarily, plants with broad leaves and laminal cells approach B. balticum, considered to be conspecific with B. barnesii. Bryum bicolor has been reported from 25 states of the United States and six Canadian provinces. Bryum barnesii, newly reported from North America, is most common along the Pacific coast, whereas both B. gemmiferum and B. gemmilucens are considered rare in North America.