Flora of North America species comparison

In North America, Ranunculus ficaria seems to be expanding its range rapidly in areas with cool mesic climates.

The species is extremely variable (especially in leaf size and stem posture), and many attempts have been made to divide it into varieties or subspecies (see P. D. Sell 1994). The different forms, however, intergrade extensively and the varieties are often impossible to distinguish.

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

Varieties 3 (3 in the flora).

In Eurasia, this taxon is usually treated as two closely related species. Ranunculus flammula in the strict sense has relatively stout (0.8-3 mm thick) stems that are erect or ascending from prostrate bases, lanceolate to oblanceolate leaves 3-10 mm broad, sepals 3-4 mm, and petals 5-7 × 3-4 mm. Ranunculus reptans has slender (0.2-1 mm thick) stems that are usually prostrate except for the pedicels, leaves linear or filiform, to 2 mm broad, sepals 1-2 mm, and petals 3-5 × 1-2.5 mm. In North America, this distinction holds up relatively well east of the Great Plains, where plants with the characteristics of R. flammula in the strict sense are found in eastern Canada (Newfoundland and northern Nova Scotia) while plants with the characteristics of R. reptans are widespread. In the western part of the continent, however, the situation is much less clear. Collections from the Great Plains and Rocky Mountains resemble R. reptans in most characters, but they often have broader leaves (up to 5 mm broad). Plants from farther west are very confusing; specimens showing the typical morphology of R. flammula in the strict sense and R. reptans are found over a wide area, but most specimens from this area combine the characteristics of the two taxa in various ways. For this reason, it is not possible to separate these taxa at the species level. Three varieties are usually recognized, but further study will probably alter the varietal classification (see comments below, under R. flammula var. ovalis).

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