Flora of North America species comparison

Rumex acetosella in the broad sense is an extremely variable and taxonomically complicated polyploid complex, which includes diploids, tetraploids, hexaploids, and octoploids. This complex (excluding more distantly related arctic-montane R. graminifolius and its allies) probably originated and developed mostly in southern Europe and southwestern Asia. Some races of R. acetosella now are distributed almost worldwide as introduced and often completely naturalized aliens.

Á. Löve (1941, 1983) assumed that in this group chromosome numbers are strictly correlated with morphology. In his opinion, every chromosome race represents a distinct species: diploid Rumex angiocarpus Murbeck [= Acetosella angiocarpa (Murbeck) Á. Löve]; tetraploid R. multifidus Linnaeus [= R. tenuifolius (Wallroth) Á. Löve = Acetosella multifida (Linnaeus) Á. Löve]; hexaploid R. acetosella in the narrow sense [= A. vulgaris (W. D. J. Koch) Fourreau, with gymnocarpous A. vulgaris subsp. vulgaris and angiocarpous A. vulgaris subsp. pyrenaica (Pourret ex Lapeyrouse) Á. Löve]; hexaploid R. graminifolius Rudolph ex Lambert [= A. graminifolia (Rudolph ex Lambert) Á. Löve]. However, the distribution given by Löve for these taxa seems unnatural. Studies by J. C. M. den Nijs and collaborators (den Nijs 1974, 1976, 1984; den Nijs and T. Panhorst 1980; den Nijs et al. 1980, 1985; see also W. Harris 1969, 1973) indicate that the situation is more complicated. They postulated the development of two major evolutionary lines into two ploidy complexes: a primary western Mediterranean one and a secondary eastern Mediterranean one. According to this scheme, polyploid races independently and spontaneously emerged (and still are emerging) within different ancestral populations.

The most widespread, almost cosmopolitan race, presumably native to the southwestern Mediterranean region, including southwestern and Atlantic Europe, which is common in North America, is characterized by a hexaploid chromosome set (2n = 42), nonmultifid lateral lobes of basal leaves, and angiocarpy (fruits are not easily separable from accrescent inner tepals). It was commonly and erroneously referred to as Rumex angiocarpus Murbeck, or R. acetosella subsp. angiocarpus (Murbeck) Murbeck. According to J. R. Akeroyd (1991), who in general followed the taxonomic revision of the group by J. C. M. den Nijs (1984), the correct name for this taxon is R. acetosella subsp. pyrenaicus (Pourret ex Lapeyrouse) Akeroyd (=Acetosella vulgaris subsp. pyrenaica (Pourret ex Lapeyrouse) Á. Löve). Gymnocarpous nonmultifid and multifid forms (R. acetosella subsp. acetosella and R. acetosella subsp. acetoselloides (Balansa) den Nijs, respectively) also occur in North America, but evidently rarely. The distributions of subspecies of R. acetosella in North America are poorly known. Keys and detailed descriptions for the subspecies were provided by den Nijs and Akeroyd. However, the tempting simplicity of the keys is somewhat suspicious. The alternative point of view (and an alternative key) may be found in Á. Löve (1983).

Rumex acetosella subsp. arenicola Mäkinen ex Elven was recently described from Greenland and reported for Scandinavia and arctic Russia (R. Elven et al. 2000). This entity seems to be morphologically transitional toward Rumex graminifolius (see discussion under that species below). According to Elven et al., it differs from other infraspecific entities of R. acetosella in having the following characters: leaves usually without basal lobes (as in R. graminifolius), with revolute margins; inflorescence sparsely branched; tepals and pedicels densely covered with red papillae (as in R. graminifolius). From R. graminifolius and related taxa (R. beringensis and R. krausei) it can be distinguished by narrower inner tepals (similar in size to those in other subspecies of R. acetosella). The distribution of subsp. arenicola and its relations to other taxa are in need of further study.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Rumex arcticus is polymorphic, as are R. aquaticus in the narrow sense and R. occidentalis. However, unlike R. aquaticus and R. occidentalus, it is represented by at least two chromosome races (G. A. Mulligan and C. Frankton 1972; Á. Löve 1986). Plants morphologically transitional between R. arcticus and R. aquaticus were described from Kamchatka as R. kamtschadalus (= R. arcticus var. kamtschadalus). The same forms occasionally occur in northwestern North America. According to Á. Löve and D. Löve (1975b) and Á. Löve (1986), they are usually tetraploids (2n = 40) and deserve recognition at the species level. However, they are not always morphologically distinct from R. arcticus. The group needs additional study, and at present I prefer to keep the tetraploid plants provisionally within R. arcticus, regarding them as var. kamtschadalus.

A few highly sterile specimens with mostly abortive flowers, which I have seen in Alaskan herbarium material, most probably represent hybrids between tetraploid and 12-ploid races of the R. aquaticus group.

Plants with unusually wide, triangular-oblong, or almost ovate leaves were described as var. latifolius Tolmatchew. This seems to be a predominant variety on the Beringian coast of Chukotka and Wrangel and Ratmanov islands (A. I. Tolmachew 1966). I also have seen at least two collections of this variety from the western coast of Alaska. The enigmatic var. perlatus Hultén may belong here (see discussion under 8. R. lapponicus).

Rumex arcticus has been reported from Churchill in northeastern Manitoba (H. J. Scoggan 1978–1979, part 3). That record needs confirmation because some northern forms of R. arcticus and R. occidentalis are similar.

(Discussion copyrighted by Flora of North America; reprinted with permission.)