Flora of North America species comparison

In North America, Grimmia trichophylla is principally a lowland species, occurring in the mountains up to about 1000 m., rarely higher. In the Southern Hemisphere, it may be found up to 4000 m. In New Zealand, the species is common, and in contrast to G. trichophylla in North America, frequently bears capsules. The New Zealand plants are usually smaller than American specimens, and the leaves are frequently contorted. The nearly cosmopolitan G. trichophylla has many phenotypes, and numerous subspecies and varieties have been described. In damp and shaded habitats, the awns may be short, just as in dry unfavorable habitats at high altitudes, where stunted specimens may occur with small, short leaves and reduced awns, or even with muticous leaves. Grimmia trichophylla has frequently been confused with related species such as 36. G. muehlenbeckii and 34. G. lisae (see discussions thereunder for identification details). Robust forms of G. trichophylla have been mistaken for G. austrofunalis (H. C. Greven 1997, 2003), which does not occur in North America. Although some of those plants have leaves of equal length along the stem, characteristic of G. austrofunalis, they also have both leaf margins recurved, and the medial and outer basal laminal cells are longer and more robust than in that species.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Grimmia sessitana is widely distributed in high elevation sites throughout western North America, principally in mountains forming the continental divide, but also in the northern Sierra Nevada and the coastal range of Oregon and Washington. It is rare in eastern North America, but occurs in the northern Appalachians of the United States, on the Gaspé Peninsula of Quebec, and in Labrador. This is the least xerophilous member of the group; specimens have been collected in runoff zones from late-lying snow patches in the alpine. It is very rare in the dry interior mountains of the American Southwest. Grimmia sessitana is gametophytically variable and often difficult to identify with certainty. The presence of stomata and the autoicous condition separate this species from both G. montana and G. alpestris, which are the most common misidentifications. Confirming the presence or absence of stomata requires careful dissection of the capsule, including the neck, as the stomata are often just distal to the attachment of the seta. Sexuality can be difficult to determine, as G. sessitana is cladautoicous. If one leaf margin is recurved this will confirm the identification. However, some specimens may have plane margins. The presence of bulging-mammillose cells should separate G. sessitana from G. montana, but a significant number of specimens of G. sessitana have only weakly bulging laminal cells. Thus, specimens with capsules and antheridia are usually identifiable, while sterile specimens may be problematic. The other species that is often confused with G. sessitana is G. donniana. Both species have capsules with stomata and are autoicous. However, G. donniana very consistently has leaves with plane margins, uniform basal areolation with hyaline, narrowly rectangular thin-walled cells, and laminal cells that do not bulge. Grimmia sessitana appeared in H. A. Crum and L. E. Anderson’s (1981) flora of eastern North America as G. tenerrima. E. Lawton (1971), who accepted autiocous specimens in the concept of G. alpestris, excluded G. sessitana from the flora of the Pacific Northwest. J. Muñoz (1998b) put G. sessitana in synonymy with G. reflexidens but this is not correct.

(Discussion copyrighted by Flora of North America; reprinted with permission.)