Leaves commonly forming a rosette, simple or compound, often palmately lobed or divided.
Flowers solitary or in cymes, actinomorphic, bisexual. Sepals usually 5. Petals usually 5 or more, rarely fewer, yellow or white [or reddish], each with a nectary towards the base and commonly covered by a nectary lobe, rarely nectaries more numerous or not ± basal. Stamens usually numerous. Carpels many.
Fruit a head of achenes, each with a short beak derived from the persistent style.
| | Key to the species | |
| 1 | Aquatic herbs with submerged leaves divided into filiform segments and with membranous stipules; petals white | Ranunculus trichophyllus |
| Terrestrial or aquatic herbs, leaf segments broader, without distinct stipules; petals yellow or white | 2 |
| 2 | Petals white | 5 |
| Petals yellow or greenish yellow
Back to 1 | 3 |
| 3 | Stolons present | 6 |
| Stolons absent
Back to 2 | 4 |
| 4 | Sepals spreading and petals more than 5 in number and flowers more than 3 mm diam | 14 |
| Either sepals reflexed or if sepals spreading then petals 1–3 and flowers less than 3 mm diam
Back to 3 | 25 |
| 5 | Robust herb mostly 15–30 cm high; leaves palmately lobed with broad overlapping segments | Ranunculus anemoneus |
| Diminutive herb 1–8 cm high; leaves pinnately divided into narrow-linear segments < 2 mm wide
Back to 2 | Ranunculus millanii |
| 6 | Petals more than 9 mm wide, with a broad-cuneate nectary lobe | Ranunculus repens |
| Petals less than 9 mm wide, nectary lobe not cuneate
Back to 3 | 7 |
| 7 | Nectary without a distinct lobe but with a thick crescentic or semicircular ridge | 8 |
| Nectary with a distinct lobe, free for most of its length or attached at sides to form a pocket
Back to 6 | 9 |
| 8 | Leaves simple, entire or with 1 tooth on each side | 32 |
| Leaves palmately divided into few or many lobes
Back to 7 | Ranunculus amphitrichus |
| 9 | Lateral faces of mature achene with 2–5 prominent, broad, oblique or nearly longitudinal ridges | Ranunculus collinus |
| Lateral faces of achenes smooth, undulate or with numerous transverse ridges
Back to 7 | 10 |
| 10 | Leaves ternate, the primary segments entire or each with 2–5 lobes, thick-textured | 11 |
| Leaves ternately or palmately divided, the primary segments with numerous lobes or teeth, thin- or thick-textured
Back to 9 | 12 |
| 11 | Petals 7–12 mm long, 2–4 mm wide | Ranunculus papulentus |
| Petals 3.5–5.5 mm long, 0.6–1.5 mm wide
Back to 10 | Ranunculus diminutus |
| 12 | Sepals glabrous; petals ± 7 mm long; receptacle almost glabrous among the achenes (although pilose in staminal zone), lateral faces of achenes smooth or irregularly undulate | Ranunculus inundatus |
| Sepals pilose; petals more than 7 mm long; receptacle pilose throughout, achenes with transverse ridges
Back to 10 | 13 |
| 13 | Achenes mostly 1.0–1.6 mm long (excluding beak), the margin not thickened | Ranunculus meristus |
| Achenes 1.8–2.5 mm long (excluding beak), the margin conspicuously thickened
Back to 12 | Ranunculus undosus |
| 14 | Leaves simple, plant glabrous or nearly so | Ranunculus flammula |
| Leaves palmately lobed or divided, or if simple then plant pilose or hirsute
Back to 4 | 15 |
| 15 | Achenes strongly compressed, stems usually branching | 16 |
| Achenes not strongly compressed, stems branched or simple
Back to 14 | 17 |
| 16 | Achenes 6–8 mm long (excluding beak) with long slender spines to 3 mm | Ranunculus arvensis |
| Achenes 3–4.5 mm long (excluding beak), lacking spines
Back to 15 | Ranunculus clivicola |
| 17 | Petals less than 4 mm wide | 18 |
| Petals more than 4 mm wide
Back to 15 | 19 |
| 18 | Petals golden-yellow, 4–9 mm long | Ranunculus pimpinellifolius |
| Petals pale yellow, 1.5–2.5 mm long
Back to 17 | Ranunculus productus |
| 19 | Achenes almost globose | Ranunculus pachycarpus |
| Achenes lens-shaped, body of achene not almost as thick as long
Back to 17 | 20 |
| 20 | Leaves simple, entire or with 1 tooth on each side | 32 |
| Leaves dissected or lobed or with more than 3 teeth
Back to 19 | 21 |
| 21 | Leaves divided into subterete or linear-lanceolate segments or lobes; petals often more than 5 | 22 |
| Leaves less divided or with broad segments or lobes; petals mostly 5
Back to 20 | 23 |
| 22 | Petals with 2 or 3 nectaries (rarely more) in shallow pits with thickened margins; leaves 2–3 times pinnately divided into linear subterete segments | Ranunculus gunnianus |
| Petals with 1 nectary with a triangular or oblong lobe; leaves once or several times ternately divided with linear-lanceolate lobes and teeth
Back to 21 | Ranunculus dissectifolius |
| 23 | Nectary lobes present | 24 |
| Nectaries in small pits without distinct lobes
Back to 21 | Ranunculus niphophilus |
| 24 | Nectary lobes broadest in upper part, usually obovate or cuneate, broader than long; flowering stems mostly branched with 2–10 flowers | Ranunculus lappaceus |
| Nectary lobes not broadest in upper part, oblong or triangular; flowering stems usually unbranched
Back to 23 | Ranunculus graniticola |
| 25 | Flowers more than 5 mm diam | 26 |
| Flowers less than 5 mm diam
Back to 4 | 30 |
| 26 | Achenes with spines or tubercles | 27 |
| Achenes lacking spines or tubercles
Back to 25 | 28 |
| 27 | Achenes 7–8 mm long with stout tapering spines on the lateral faces and a stout slightly recurved beak c. 3–4 mm long | Ranunculus muricatus |
| Achenes 2–3 mm long with short blunt tubercles on the lateral faces, and a short beak
Back to 26 | Ranunculus trilobus |
| 28 | Achenes less than 1 mm long, with a minute beak, numerous (40–300), in an elongated head | Ranunculus sceleratus |
| Achenes more than 1 mm long, with a distinct beak, few to many in a globose head
Back to 26 | 29 |
| 29 | Achene beak less than 1 mm long, strongly recurved | Ranunculus plebeius |
| Achene beak more than 1 mm long, straight or arching with a recurved tip
Back to 28 | Ranunculus scapiger |
| 30 | Achenes 2–4 mm long, very thin (laterally compressed), usually twisted when mature, with a thickened margin | Ranunculus pentandrus |
| Achenes 1.5–2 mm long, not strongly compressed or twisted
Back to 25 | 31 |
| 31 | Achenes smooth and glabrous or with numerous small tubercles bearing hairs longer than the distance between the tubercles | Ranunculus pumilio |
| Achenes with prominent conical tubercles bearing recurved hairs shorter than the distance between tubercles
Back to 30 | Ranunculus sessiliflorus |
| 32 | Leaves with petiole longer than lamina | Ranunculus muelleri |
| Leaves with petiole shorter than lamina
Back to 20 | Ranunculus acrophilus |
