Panarctic Flora

310101-03 The Sparganium angustifolium-emersum aggregate S. angustifolium, S. emersum, S. multipedunculatum

Geography: Circumboreal-polar.

Notes: Sparganium angustifolium and S. emersum (S. simplex) are considered two species in Eurasia. They hybridize frequently (as do most species of Sparganium) but the hybrids are largely sterile (e.g., Hylander 1953b) and do not compromise the species.

The current North American view differs. Kaul (2000): "Sparganium emersum is easily confused with S. angustifolium" and "the entire S. emersum-S. angustifolium complex ... is perhaps better treated as one variable species, S. angustifolium". Eurasian and North American material of S. angustifolium (described from Canada) should be critically compared; European authors may have misunderstood the species. Another possible reason for the discrepancy may be S. multipedunculatum. Hultén (1962) discussed S. multipedunculatum in the context of S. simplex (= S. emersum), not vs. S. angustifolium, which he, from an European viewpoint, probably found to be as different from S. emersum as not to be part of the problem. The differences he noted were that S. multipedunculatum has shorter and thicker stigmas than S. emersum and more approximate staminate heads. These quantitative features might justify races rather than species. Reveal (1970) discussed the case and accepted S. emersum var. multipedunculatum.

Kaul (2000) included "multipedunculatum" in the synonymy of S. angustifolium. He did not acknowledge that, at least until the 1970's, the name "multipedunculatum" had been applied to a taxon closer to or part of S. emersum, not S. angustifolium. Whereas S. multipedunculatum connects S. angustifolium and S. emersum in North America is not known. However, the material we have seen of S. multipedunculatum from northwestern North America differs from both the Eurasian and Alaskan material of S. angustifolium. We accept all three taxa as species.