Stems prostrate or sometimes ascending, 0.5-2 mm thick. Leaf blades lance-elliptic to lanceolate or linear, 0.8-3.3 × 0.2-0.8 cm. Flowers: sepals 2-3 mm; petals 3-5 × 2-3 mm. 2 n = 32. Flowering spring-summer (May-Sep). Muddy ground or shallow water; 0-2900 m; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask.; Alaska, Ariz., Calif., Colo., Conn., Idaho, Maine, Mass., Mich., Minn., Mont., Nev., N.H., N.Mex., N.Y., N.Dak., Oreg., Pa., Utah, Vt., Wash., Wyo. Ranunculus flammula var. ovalis , as currently understood, is heterogeneous. Many specimens from throughout the cited range scarcely differ from specimens of R . flammula var. reptans and perhaps should be included in the latter variety. Material from the Pacific slope, however, may be intermediate between R . flammula var. reptans and R . flammula var. flammula or may show various combinations of the distinguishing characteristics of the two. Biosystematic study of R . flammula as a whole will be needed for a meaningful treatment of these populations to be possible.
Lvs entire or slightly toothed; pet obovate, mostly 3-7 mm, about twice as long as the sep; achenes 1.3-1.7 mm, the erect or ascending beak 0.2-0.5 mm. 2n=32. Sandy or muddy shores; circumboreal, s. to Mass., Pa., Mich., Minn., and the western cordillera. July-Sept. Our commonest phase is the circumboreal var. filiformis (Michx.) DC., slender, prostrate, and creeping, 1-5 dm long, sending up at each node a few lvs and a naked or few-lvd, 1-fld stem 3-15 cm, the lvs filiform or linear, with scarcely expanded blade to 1.5 mm wide; 2n=32. (R. reptans) The very similar var. ovalis (Bigelow) L. D. Benson, with expanded blades mostly 1.5-7 mm wide, is sporadic with us but common farther west. The chiefly Eurasian var. flammula, in our range restricted to N.S., is stouter, with ascending or reclining stems 1-5 dm, sometimes rooting at the lower nodes but not creeping, branched above and with several fls, and with the lvs mostly 3-10 mm wide.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.