Panarctic Flora

3309078-080 The Carex aquatilis aggregate C. aquatilis, C. concolor, C. sitchensis

Geography: Circumboreal-polar.

Notes: The Carex aquatilis aggregate is a polymorphic and probably heterogeneous (polyphyletic) group of taxa. Numerous authors (e.g., Hultén 1962, 1968a; Egorova 1966a; Chater 1980; Porsild and Cody 1980; Elven et al. 2005) have accepted the same two or three taxa for their regions as C. aquatilis s. str. (subsp. aquatilis), C. stans (C. aquatilis subsp. stans, C. concolor), and C. sitchensis (C. aquatilis var. dives, C. dives). Standley et al. (2002) recognized four regional varieties of C. aquatilis in North America, three of them to reach the Arctic: var. aquatilis, var. dives (= C. sitchensis), and var. minor (= C. stans, C. concolor). We accept three species under the names C. aquatilis, C. concolor, and C. sitchensis.

The mainly boreal C. aquatilis and the arctic-alpine C. concolor (C. stans) differ in habit and in several details, not least the greyish papillose leaves of C. aquatilis vs. the yellowish green, non-papillose leaves of C. concolor, but also distant pistillate spikes vs. more congested ones, pistillate scales narrower than the perigynia and with a broad green middle part vs. as broad as the perigynia and with a narrow pale or green stripe, and the few retained leaf remains of C. aquatilis vs. the abundant ones covering the base of the shoots of C. concolor for several years. The ranges of C. aquatilis and C. concolor strongly overlap. Transitions are reported to be common in the meeting zones but have not been confirmed by any critical investigation (in Norway, these "transitions" have been extensively identified, erroneously, as C. aquatilis x bigelowii). The reproductive features of the suggested transitions are not known.

The majority of authors have preferred to accept two subspecies (subsp. aquatilis and subsp. stans), besides C. sitchensis. Treatment as subspecies can be justified but some molecular studies support a split on two or more species. In addition, there may be some delimitation problems towards C. bigelowii s. lat. In the analysis of AFLP data by Nakamatte and Lye (2008), C. aquatilis is split on two branches, one with samples from Newfoundland joining with C. concolor from Greenland and C. bigelowii from Quebec and northwestern Norway (probably subsp. bigelowii), another with samples from Labrador and northern Finland and joining, more or less, with C. bigelowii from southern Norway (subsp. rigida). This separation of C. bigelowii is supported by the analyses of Schönswetter et al. (2008; AFLPs) but these authors did not include C. aquatilis s. lat. In the analysis of ITS data by Hendrichs et al. (2004) and of ITS, ETS, and cpDNA data by Dragon and Barrington (2008, 2009), C. aquatilis kept consistently apart from C. bigelowii, but in the study of Dragon and Barrington proved quite variable, supporting at least three clades with posterior probabilities > 50%: (1) plants from Finland and Russia, probably C. aquatilis s. str.; (2) plants from Utah, Vermont, and Alaska, partly as var. minor = C. concolor and as var. substricta; and (3) plants from California, Washington, and Alaska assigned to var. dives = C. sitchensis. The support for these clades was at level with support between accepted species or species groups in other parts of Phacocystis, suggesting that the view of C. aquatilis as one species with varieties needs revision. In fact, the entire C. aquatilis-bigelowii complex needs a more thorough combined molecular and morphological analysis.