Panarctic Flora

330704 Eleocharis macrostachya Britton

• Britton in Small, Fl. S.E. U.S.: 184 (1903). Type: U.S.A.: "Indian Territory" Oklahoma, leg. Palmer 264a.

2n= (1) 16 (ca. 2x). - Canada, U.S.A. - Heiser and Whitaker (1948); Taylor and Mulligan (1968); Ward (1984).
(2) 38 (ca. 4x). - Canada, U.S.A. - Strandhede (1967); Harms (1968); Kessler (1983).
Smith et al. (2002) reported the chromosome numbers as 2n = 18, 19, and 38. They stated that the numbers 2n = 10 (Heiser and Whitaker 1948, southwestern U.S.A.) and 16 had not been verified. We have not found primary sources for 2n = 18 or 19.

Geography: North American & South American: (CAN).

Notes: Eleocharis macrostachya is reported from the Borderline Arctic on Hudson Bay west of the entrance to James Bay. In the west it approaches the Arctic in Alaska, whereas it in the Yukon Territory is restricted to the southern parts (ALA). The two main different chromosome numbers reported might represent different taxa (compare with E. palustris).

Ball: The arctic plants that Smith et al. (2002) included in this species belong to a distinct unnamed variant. The problem is that this taxon is an aggregate of plants that are intermediate between the palustris group and the uniglumis group, and Smith's three variants are derived from different hybrid combinations of these two groups.

Elven: Smith et al. (2002) considered E. macrostachya (especially their variety b with 2n = ca. 38) to be the American counterpart of E. palustris subsp. vulgaris, which they on the other hand considered "morphologically intermediate between E. palustris and E. uniglumis and may be of hybrid origin". The latter supposition is contrary to European morphological evidence. Eleocharis palustris subsp. vulgaris differs more morphologically from E. uniglumis than does E. palustris subsp. palustris and is not intermediate. In addition, we find American E. macrostachya (ALA specimens) to differ in several features from European E. palustris subsp. vulgaris.