Flora of North America species comparison

Rumex crispus (belonging to subsect. Crispi Rechinger f.; see K. H. Rechinger 1937) is the most widespread and ecologically successful species of the genus, occuring almost worldwide as a completely naturalized and sometimes invasive alien. It has not been reported from Greenland, but it probably occurs there.

Rumex crispus hybridizes with many other species of subg. Rumex. Hybrids with R. obtusifolius (Rumex ×pratensis Mertens & Koch) are the most common in the genus, at least in Europe, and have been reported for several localities in North America. Rumex crispus × R. patientia (Rumex ×confusus Simonkai) was reported from New York. According to R. S. Mitchell (1986, p. 47), “this hybrid is now spreading along highway shoulders, and it has replaced R. crispus in some local areas.” However, that information should be confirmed by more detailed studies since spontaneous hybrids between species of sect. Rumex usually are much less fertile and ecologically successful than the parental species. Hybrids of Rumex occuring in North America need careful revision.

Numerous infraspecific taxa and even segregate species have been described in the Rumex crispus aggregate. Many seem to represent minor variation of little or no taxonomic significance, but some are geographically delimited entities that may deserve recognition as subspecies or varieties. The typical variety has inner tepals with three well-developed tubercles; the less common var. unicallosus Petermann, with one tubercle, occurs sporadically in North America.

Some eastern Asian plants differ from typical Rumex crispus is having somewhat smaller inner tepals, longer pedicels, lax inflorescences with remote whorls, and narrower leaves that are almost flat or indistinctly undulate at the margins. These plants, originally described as R. fauriei Rechinger f., are now treated as R. crispus subsp. fauriei (Rechinger f.) Mosyakin & W. L. Wagner; the subspecies was recently reported from Hawaii (S. L. Mosyakin and W. L. Wagner 1998) and may be expected as introduced in western North America.

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

Rumex paucifolius is a montane species represented by two chromosome races (diploid and tetraploid) and several ecotypes. Smaller plants from California have been described as var. gracilescens; they are tetraploids and sometimes were regarded as a separate species (Á. Löve and V. Everson 1967; Löve 1986). B. W. Smith (1968) showed that both diploids and tetraploids (and even exceptional spontaneous triploids and individuals with higher polyploid chromosome numbers) occur in many other localities within the range of the species; the differences in chromosome number are not strictly correlated with distribution or morphology. Narrow-leaved ecotypes of R. paucifolius reported by Smith sometimes resemble other narrow-leaved taxa of subg. Acetosella, especially R. beringensis. Rumex paucifolius and R. beringensis may be regarded as morphologically and karyologically transitional between subg. Acetosella and subg. Acetosa. Rumex paucifolius was placed in the monotypic subsect. Paucifoliae Á. Löve & N. Sarkar. Later, Löve transferred it to the segregate genus Acetosella, based mostly on the chromosome number of the species, but morphology suggests it is a member of subg. Acetosa. Probably the best solution of this problem was proposed by Smith, who noted that “the composite range of vegetative, reproductive, and karyotypic characteristics of the forty-odd species now included in the diversified subgenus Acetosa would be only slightly extended by the addition of the five species now classified as Acetosella” (p. 683).

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