Flora of North America species comparison

Oxalis debilis appears to be spreading rapidly in the United States. The species produces numerous bulblets in a basal cluster and apparently also can spread laterally by production of bulblets at the tips of filiform roots or rhizomes; it can form large, dense colonies. A. Lourteig (1980) noted that plants of this species occasionally fruit but consistently reproduce through abundant bulblets. They apparently are seed-sterile in North America.

Oxalis corymbosa and O. debilis were differentiated by A. Lourteig (2000) primarily by the distribution of oxalate deposits in the leaf lamina. In O. debilis, the dotlike deposits are crowded along the margins and absent to distinctly less abundant elsewhere. In O. corymbosa, the deposits are evenly distributed over the whole lamina. In their native range in South America, the two expressions are broadly sympatric and intermediates are common, as they are in the flora area. Intermediates have the oxalate dots along the margins as well as over the whole surface or sometimes mostly on the outer third of the blades, near the margins. There is no justification for formal recognition of two entities.

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

Oxalis montana of eastern North America and O. oregana of the Pacific region have sometimes been treated as disjunct geographical taxa of the European (or Eurasian, depending on taxonomic interpretation) O. acetosella Linnaeus. The three are very similar and surely are closely related. Section Acetosellae Reiche also includes the Asian O. griffithii Edgeworth & Hooker f., O. leucolepsis Diels, and O. obtriangulata Maximowicz, as well as O. magellanica G. Forster (South America, New Zealand, Tasmania); the first two of these also have been treated as taxa within O. acetosella (see synonyms in Liu Q. R. and M. F. Watson 2008). Among all these, typical O. acetosella, the two American taxa, and O. magellanica have erect flowers, while those of the strictly Asian taxa are distinctly nodding, perhaps suggesting that the latter are monophyletic.

Oxalis oregana stands apart from O. montana and typical O. acetosella in its larger leaves and flowers and its strigose-villous (versus glabrous) sepals. Each of the three is distinct in petal coloration and this difference between O. acetosella and O. montana is perhaps the only one between them besides the geographical disjunction. In O. montana, the orange-yellow region near the petal base is constricted to a spot (versus a lateral band in typical O. acetosella) and a light and diffuse but distinct rose colored band lies immediately distal to the spot, connecting among the petals to form a circle. Oxalis acetosella in the strict sense occurs from Iceland to southern Europe (and possibly northern Africa), reportedly stretching as a broad band completely across Eurasia to Japan to Korea (J. F. Veldkamp 1971; Liu Q. R. and M. F. Watson 2008). Attributions of O. acetosella to Pakistan and other Himalayan localities apparently are based on plants of O. griffithii.

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