Publication: Sp. Pl. 1: 548.
selected vouchers: WTU
Notes: FNA3: "In Eurasia, this taxon [R. flammula] 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.
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 ).
L. D. Benson (1948) reported Ranunculus flammula var. flammula only from eastern Canada and referred all material from the Pacific Slope to Ranunculus flammula var. ovalis . Benson's treatment is not tenable, however, because some western collections are indistinguishable from the eastern plants."