Flora of North America species comparison

Of conservation concern.

Previous to its discovery in Iceland, as Grimmia grisea (H. C. Greven 1998), G. reflexidens was known from only the Southern Hemisphere. It had previously been collected east of East Bay, Newfoundland, now the only known locality in North America, but was not recognized as G. reflexidens. The latter is similar to G. asperitricha Dixon & Sainsbury of New Zealand, and the two species have been confused by G. O. K. Sainsbury (1945) as well as by R. Ochyra (1993). J. Muñoz (1998b) synonymized G. reflexidens with G. sessitana. However, the former is readily separated from the latter by: (1) enlarged perichaetial leaves, (2) decurrent awns, (3) non-bulging laminal cells, and (4) dioicous sexual condition. Capsules are unknown from Northern Hemisphere material, but G. reflexidens lacks stomata while they are present for G. sessitana. Although G. reflexidens and G. teretinervis both have decurrent awns they are easily separated by a number of characters: G. reflexidens grows in compact cushions, has long awns, and a semicircular costa; G. teretinervis grows in loose clumps, is hyaline-tipped to short-awned, and has a unique costa that is distally almost completely circular in transverse section.

(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.)