Description from Flora of China
Ranunculus arcuans S. S. Chien; R. cantoniensis de Candolle var. sieboldii (Miquel) Kitamura ex Hatusima; R. pensylvanicus Linnaeus var. sieboldii (Miquel) Ito; R. sardous Crantz var. monanthos Finet & Gagnepain; R. sieboldii var. arcuans (S. S. Chien) H. Hara.
Herbs perennial. Roots fibrous, subequally thick. Stems ascending or subprostrate, 8--50 cm, hirsute, branched, rarely simple, rooting at lower nodes. Basal leaves 3--7; petiole 2.5--14 cm, hirsute; blade ternate, ovate in outline, 1.5--5.4 × 2.6--7 cm, papery, strigose; central leaflet petiolulate, broadly rhombic or broadly rhombic-ovate, margin 3-cleft to middle, few dentate; lateral leaflets petiolulate, obliquely broadly obovate, unequally 2-lobed or 2-partite. Stem leaves similar to basal ones, with shorter petioles. Flowers leaf-opposed, 0.9--1.8 cm in diam. Pedicel 0.7--4.6 cm, densely strigose. Receptacle puberulent. Sepals 5, reflexed, narrowly ovate, 4--6 mm, abaxially strigose. Petals 5, narrowly obovate or long elliptic, 5--9 × 2.5--4 mm, nectary pit covered by a scale, apex rounded. Stamens numerous; anthers oblong. Aggregate fruit subglobose, 8--10 mm in diam.; carpels numerous. Achene flat, obliquely obovate, 3--4 × 2.2--3 mm, glabrous, broadly marginate; style persistent, ca. 1 mm, curved at apex. Fl. Mar--Oct.
Ranunculus taiwanensis Y. C. Liu & F. Y. Lu (Quart. J. Chin. Forest. 11 (3): 108. 1978), is known only from the type, which could not be located. The protologue, particularly the description of 4 mm long achenes, suggests a relationship to R. sieboldii . However, the leaves of R. taiwanensis are more divided, and Michio Tamura (pers. comm.) believes that it is a distinct species.
Grassy places, scrub, by rivers; 50--2500 m. S Anhui, Fujian, S Gansu, W and N Guangxi, Guizhou, S Henan, Hubei, Hunan, S Jiangsu, Jiangxi, S Shaanxi, N Shandong, Sichuan, Taiwan, NE Yunnan, Zhejiang [Japan].