Panarctic Flora

344303-05 The Alopecurus magellanicus aggregate A. borealis, A. glaucus, A. stejnegeri

Geography: Circumpolar-alpine & South American (S).

Notes: Elven and Murray: The Alopecurus magellanicus aggregate is present both in northern-alpine and arctic areas and in southern South America, separated by a wide gap across the tropical and subtropical belts. The disjunction between the northern and southern hemisphere plants is probably not recent as the southern plants have an extensive range from Peru south to Tierra del Fuego with two named varieties. Soreng et al. (2003), followed by Crins (2007b), merged the northern hemisphere plants named as A. alpinus Sm., A. borealis Trin., A. glaucus Less., A. rozhevitzianus Ovcz., and A. stejnegeri Vasey within one species under the South American priority name A. magellanicus Lam. They did not suggest any racial name(s) for or differentiation among the northern plants, but their main focus seems to have been on the southern hemisphere plants.

Alopecurus magellanicus Lam., Tabl. Encycl. 1: 168 (1791), was described from the southernmost South America and with holotype (P) from southern Chile: "Magallanes", leg. Commerson. A second name, A. antarcticus Vahl, Symb. Bot. 2: 18 (1791), is probably based on the same (Commerson) collection as Lamarck's name but was, according to Stafleu, published slightly later in the same year. This South American plant is known to be a high-polyploid with 2n = 112 and 116 (Johnsson 1941). The northern plants are also highly and variably polyploid (2n = ca. 70-ca. 150). We have investigated northern plants for possible signs of agamospermy but have found them to have at least fully developed pollen.

The variation among the northern plants was not resolved by Soreng et al. (2003) or Crins (2007b), and we disagree with Crins' conclusion that all the northern variation is part of an environmentally determined continuum. We are not aware of any molecular or morphological support for a merger of the southern and northern hemisphere plants within one species. We accept that A. magellanicus belongs in this aggregate. However, we refrain from accepting it as name for the northern plants until the northern and southern hemisphere plants are better compared and until the variation among the northern plants (which is appreciable) is recombined as races of A. magellanicus. We assume that several new combinations at subspecific level must be made if only one species (A. magellanicus) is accepted. We are also very reluctant to accept that the northern plants fit into a subspecific model as transitional forms are rare, at best.

The northern plants have been treated as several species or races with the major parts of the variation in the broadly amphi-Pacific/Beringian regions. We find the material to group on three main taxa with different but overlapping geographical ranges and with very few morphological transitions in the meeting zones. We accept three species: the circumpolar and alpine A. borealis, the mainly boreal-alpine northern Asian and Cordilleran A. glaucus, and the narrowly amphi-Beringian A. stejnegeri. We have seen no signs that the differences among these plants are environmentally determined as suggested by Crins (2007b).