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.)

The name Rumex acetosa has been commonly misapplied to R. lapponicus. Native North American montane plants of the R. acetosa aggregate from the Rocky Mountains southward to Beartooth Plateau in Montana and Wyoming usually were referred to as R. alpestris [= Acetosa pratensis Miller subsp. alpestris (Jacquin) Á. Löve; A. pratensis subsp. arifolia (A. Blytt & O. C. Dahl) Á. Löve; R. arifolius Allioni, not Linnaeus f.; R. acetosa subsp. alpestris (Jacquin) Á. Löve; R. acetosa subsp. arifolius A. Blytt & O. C. Dahl]. Recent nomenclatural studies demonstrated that R. alpestris is an ambiguous name, which was probably based on plants belonging to R. scutatus Linnaeus (see I. O. Pestova 1998), and accepted the name R. arifolius for the predominantly European montane taxon. It differs from arctic plants, as well as from montane forms of the R. acetosa aggregate from southern Siberia and temperate North America, by its more robust habit, more branched inflorescence (similar to that of R. thyrsiflorus), and larger and more acute triangular-sagittate leaves (see A. I. Tolmachew 1966; N. N. Tzvelev 1989b; Pestova; R. Elven et al. 2000). Montane races possibly developed independently from R. lapponicus-like or R. acetosa-like ancestors, and they are still unclear taxonomically. Because of that, I prefer to keep those forms within R. lapponicus. The whole aggregate needs careful study; however, some authors prefer to include all arcto-montane Holarctic races of this aggregate in the collective and rather polymorphic R. alpestris in the broad sense (see Á. Löve 1944; Löve and D. Löve 1957).

Some arctic plants from western Alaska may be conspecific with Rumex pseudoxyria (Tolmatchew) Khokhrjakov [= R. acetosa subsp. pseudoxyria Tolmatchew; Acetosa pseudoxyria (Tolmatchew) Tzvelev], a taxon described from arctic eastern Siberia (A. I. Tolmachew 1966). This entity is evidently closely related to R. lapponicus but differs from all other members of the R. acetosa group in having basal leaves less than two times as long as wide, almost hastate or at least rounded-truncate at base, resembling those of Oxyria digyna (Linnaeus) Hill, cauline leaves small or completely reduced, and inflorescence occupying more than one-half of the stem; the plant itself is also somewhat similar in appearance to the European alpine species R. nivalis Hegetschweiler.

According to E. Hultén (1973), his Rumex arcticus var. perlatus, described from a single specimen collected at Tin City, Seward Peninsula, Alaska, agrees perfectly with the original description of R. acetosa subsp. pseudoxyria. It is unlikely that Hultén would confuse two rather distantly related groups. There is also a possibility that var. perlatus is identical with R. arcticus var. latifolius Tolmatchew (see discussion under R. arcticus). Additional collections are needed to confirm the occurrence of R. pseudoxyria in northwestern North America.

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