Flora of North America species comparison

Sarmentypnum exannulatum is one of the most frequent wetland species, with leaves that narrow gradually to the apex and are gradually curved throughout. The marginal laminal cells in the widest part of the stem leaves are often distinctly rectangular, distinctly widened, or both; this feature is never as pronounced in other species of Sarmentypnum as in S. exannulatum. However, because this feature is rather variable it should be used with caution when identifying material. Warnstorfia fluitans and W. pseudostraminea differ from S. exannulatum in being autoicous, having mainly narrowly triangular to lanceolate pseudoparaphyllia, hardly ever with pure red pigments, and with more weakly differentiated alar regions. The alar regions in W. fluitans usually reach less far distally in the leaf than in S. exannulatum, whereas those in W. pseudostraminea often form ovate regions together with the supra-alar cells. Phenotypes of S. exannulatum, found in springs, with inflated alar cells in more or less one row along the leaf base have been called W. exannulata var. purpurascens. However, transitions between these phenotypes and those from other habitats exist, and if the different phenotypes are cultivated together, the resulting plants cannot be separated (based on north European material).

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

Sarmentypnum trichophyllum is occasionally reminiscent of S. exannulatum, but the distinctly pencil-like branch and shoot apices, excurrent costa and long, brown axillary hairs when young (shorter and normally hyaline in S. exannulatum) separate it. For the differences between S. trichophyllum and Drepanocladus longifolius, see discussion of the latter. Sarmentypnum trichophyllum has been reported from many areas of Canada (R. R. Ireland et al. 1987); however, it seems to be widespread only in western Alaska, and few specimens from outside this area have proved to belong to this species. The species was reported from two localities in Greenland by G. S. Mogensen (1995), but those specimens are S. exannulatum. In northern Europe, S. trichophyllum has been found at higher altitudes (750 m), and there is no reason to assume that the species is restricted to lower elevations in North America.

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