Sarmentypnum exannulatum
Sarmentypnum tundrae
leaves ovate or ovate-triangular, gradually narrowed to apex, falcate or strongly so, sometimes straight, concave;
base not decurrent;
margins distinctly denticulate proximally, distally, or both;
apex acuminate, sometimes furrowed but not strongly so;
costa ending 3/5 to nearly entire leaf length;
alar region from margins to costa or nearly so;
marginal cells at widest part of leaf often differentiated from medial cells.
leaves ovate or ovate-triangular, gradually narrowed to apex, slightly falcate or straight, slightly concave;
base broadly long-decurrent;
margins denticulate proximally, entire or sparsely denticulate distally;
apex broadly acuminate;
costa ending 2/3–9/10 leaf length;
alar region from margins almost to costa.
Sarmentypnum exannulatum
Sarmentypnum tundrae
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 tundrae shares no morphological apomorphies with other species in Sarmentypnum or with species of Calliergon. The species is here included in Sarmentypnum from molecular evidence. Sarmentypnum tundrae differs from all other members of the genus by its long and more or less broadly decurrent stem leaves. Additional features that aid in separating this species from S. exannulatum and S. procerum are the rather weakly falcate stem leaves and the total lack of red pigment. The leaf apex is often hooked. Sarmentypnum tundrae has been incorrectly reported from Australia.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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