1	All leaves simple and unlobed.		(2)
+	Some or all leaves simple and lobed, or compound.		(9)
2 (1)	Cauline leaves absent or scalelike; sepals deciduous or persistent.		(3)
+	Cauline leaves present, well developed; sepals deciduous.		(5)
3 (2)	Petals 5; achene beak 0.1-0.2 mm; plants stoloniferous, without caudices.		2 Sect. Halodes
+	Petals 8-18; achene beak 0.8-1.4 mm; plants not stoloniferous, stems erect from short caudices.		(4)
4 (3)	Leaf blades undivided, margins entire or serrulate; sepals persistent in fruit; petals 7-12 mm.		Ranunculus
+	Leaf blades shallowly lobed, margins crenate; sepals deciduous; petals 2-4 mm		2 Sect. Pseudaphanostemma
5 (2)	Tuberous roots present; flowers yellow; sepals 3.		2 Ranunculus
+	Tuberous roots absent (roots thickened proximally in some 5-sepaled species of sect. Flammula); flowers yellow, white, or pink.		(6)
6 (5)	Achenes 4.2-5.2 mm, achene body prolonged beyond seed as corky distal appendage; sepals 3, 6-10 mm; petals white to pink.		Ranunculus
+	Achenes 0.8-2.8 mm, achene body not prolonged beyond seed; sepals (3-)4-5, 1.5-12 mm; petals yellow.		(7)
7 (6)	Sepals covered with dense brown pubescence; distal leaves and bracts apically 3-crenate or shallowly 3-lobed, otherwise undivided.		2 Sect. Epirotes
+	Sepals glabrous or with colorless hairs; distal leaves simple and undivided.		(8)
8 (7)	Achene wall papery, longitudinally ribbed; leaf apex broadly rounded to truncate, margins crenate.		2 Sect. Halodes
+	Achene wall thick, not ornamented, smooth (sometimes pubescent); leaf apex acuminate to rounded-obtuse, margins entire or finely toothed.		2 Sect. Flammula
9 (1)	Leafy stems creeping and rooting at nodes or floating in water, then rootless.		(10)
+	Leafy stems erect or if decumbent rooting only at base, never floating.		(14)
10 (9)	Leaves 3-foliolate.		2 Sect. Ranunculus
+	Leaves simple, lobed to filiform-dissected or occasionally undivided.		(11)
11 (10)	Achene body prolonged beyond seed as corky distal appendage; sepals 3, petals 5-11.		(12)
+	Achene body not prolonged beyond seed; either sepals 5 or sepals 3-4 and petals also 3-4.		(13)
12 (11)	Leaf blade as wide as long, ternately divided to base.		Ranunculus
+	Leaf blade much longer than wide, unlobed or lobed.		Ranunculus
13 (11)	Petals white or white with yellow claws; achenes with strong coarse wrinkles.		2 Subg. Batrachium
+	Petals yellow; achenes smooth (faintly wrinkled in R. sceleratus var. sceleratus).		2 Sect. Hecatonia
14 (9)	Petals pure red, or white when immature; fruits winged achenes or utricles.		2 Subg. Crymodes
+	Petals yellow, rarely also with some red pigmentation abaxially, or greenish yellow; fruits achenes, rarely winged.		(15)
15 (14)	Cauline leaves absent or scalelike, tuberous roots absent; leaves sometimes deeply parted or dissected, never compound.		(16)
+	Cauline leaves present, simple, lobed or dissected, or compound (rarely reduced to scales in R. fascicularis with tuberous roots and 3-5-foliolate leaves).		(18)
16 (15)	Plants villous; sepals 3-6 × 1-2 mm, persistent in fruit; fruit wall firm, smooth, beak much longer than achene body.		2 Subg. Ceratocephala
+	Plants glabrous; sepals 6-13 × 3-7 mm, deciduous in fruit; fruit wall thin, veined, beak much shorter than achene body.		(17)
17 (16)	Leaves shallowly 5-7-lobed; petals inconspicuous, 2-4 mm.		2 Sect. Pseudaphanostemma
+	Leaves 3-5-parted; petals showy, 8-12 mm.		2 Sect. Arcteranthis
18 (15)	Style absent, stigma sessile; achene margins thick and corky; emergent aquatic, sometimes also found on very wet soil.		2 Sect. Hecatonia
+	Style present; achene margins not corky; in various habitats but rarely aquatic.		(19)
19 (18)	Achene wall thin, longitudinally striate; scale of nectary reduced to low ridge, not covering nectary.		2 Sect. Cyrtorhyncha
+	Achene wall thick, smooth, papillose, or spiny; scale of nectary well-developed flap or pocket completely covering nectary.		(20)
20 (19)	Achenes thick-lenticular or asymmetrically thick-lenticular to compressed-globose, 1.2-2 times as wide as thick; nectary scale joined with petal on 3 sides, forming pocket enclosing nectary (sometimes with apex free, forming flap shorter than pocket); basal leaves various, unlobed to deeply divided, margins entire to crenate but never at all serrate.		2 Sect. Epirotes
+	Achenes strongly flattened, at least 3-15 times as wide as thick; nectary scale free from petal for at least 1/2 its length, thus forming free scale over nectary (scale sometimes free for less than 1/2 its length in R. recurvatus, with serrate to crenate-serrate leaf margins); basal leaves always deeply lobed or compound (except sometimes in R. marginatus and R. orthorhynchus), margins various.		(21)
21 (20)	Achenes papillose or spiny (sometimes smooth in R. sardous); flowers small, petals 1-6 mm, scarcely longer than sepals, sometimes absent (larger and much longer than sepals in R. sardous).		2 Sect. Echinella
+	Achenes smooth, glabrous or pubescent; flowers small to large, petals always present, 2-22 mm.		2 Sect. Ranunculus