Citation: L., Sp. Pl. 548 (1753).

Derivation: Diminutive of Latin rana, a frog; name of a plant in the writings of Pliny.

Synonymy: Not Applicable

Common name: Buttercups, ranunculus.

Description:
Annual or perennial herbs, sometimes aquatics; stems erect, creeping or stoloniferous; leaves spirally arranged, often with a basal rosette, exstipulate but petioles, with a gradually tapering leaf sheath; blades often palmately lobed or divided, ternate or pinnately dissected, sometimes simple and entire.

Flowers solitary and terminal, sometimes in cymose panicles, bisexual, regular, all parts arranged spirally; sepals 3-5; petals 5-15, rarely fewer, yellow or white, often glossy, each with a nectar-secreting pit on the upper surface usually in the lower half, often near the base, sometimes covered by a lobe which may be adnate at its lateral margins forming a pocket; stamens numerous, rarely only 5 or fewer; carpels free, usually numerous, with 1 basal ovule.

Fruit a globular or elongated head of achenes; style usually persistent and forming a glabrous beak.

Distribution:  More than 500 species, cosmopolitan but chiefly in the extratropical Northern Hemisphere. In Australia about 47 species of which 10 are introduced.

Biology: Poisonous to cattle when fresh.

Key to Species:

1. Plants perennial; achenes glabrous, smooth or obscurely and irregularly rugose
2. Plants with stolons; basal leaves ternate or palmately lobed or dissected
3. Stolons above ground, thick; petals 5-10 mm wide; basal leaves ternate; leaflets broad, ovate to more or less rhombic; ripe achenes smooth, finely punctulate; beak less than half achene length	R. repens 10.
3. Stolons underground, thin; petals less than 5 mm wide; basal leaves palmatisect or palmatifid, if ternate, then leaflets narrow-elliptic to obovate-cuneate; ripe achenes obscurely rugose; beak half to two thirds achene length
4. Petals more or less linear, 3-nerved, the central nerve sometimes forked above the middle; nectary about one-third the petal length above base, forming a swollen semilunar bracket or pocket; leaves variable; segments from linear (when sub-merged) to obovate-cuneate (when aerial); sepals glabrous . R. rivularis 11
4. Petals oblanceolate to elliptic, 3-nerved at base, lateral nerves forked below the middle; nectary near the petal base, covered by a lobe, its sides often attached in part to the petal and forming a pocket
5. Ultimate leaf-segments narrow-linear, c. 1 mm wide; sepals glabrous; flowers 1-1.5 cm diam.; torus glabrous between the achenes, more or less densely short-hispid in the staminal zone	R. inundatus 2.
5. Ultimate leaf-segments narrow-elliptic-cuneate to oblanceolate, 2-6 mm wide; sepals usually hispid outside; flowers 1.5-2 cm diam., torus hispid between the achenes, glabrous in the staminal zone	R. papulentus 6.
2. Plants without stolons; basal leaves 3-lobed, 3-partire to more or less biternately cut or lobed
6. Stem and petioles with short appressed hairs throughout; basal leaves few, dissected into narrow almost linear segments; roots fleshy, more or less tuberous	R. robertsonii 12.
6. Stem and petioles with long spreading hairs at least in their lower part; basal leaves several to many, with broad lanceolate to obovate segments
7. Achenes more or less globular, with very thick pericarp; roots fleshy, more or less tuberous; basal leaves usually simple, 3- lobed to 3-partire, broad-ovate or as wide as long	R. pachycarpus 5.
7. Achenes lenticular, with thin pericarp; roots fibrous (sometimes thick); basal leaves usually ternate (at least the later ones), to biternately lobed, ovate in outline, longer than wide, the central leaflet distinctly longer stalked than the lateral leaflets	R. lappaceus 3.
1. Plants annual
8. Achenes smooth and glabrous on lateral faces; torus glabrous; sepals spreading; petals 1-4; flowers inconspicuous, 2-4 mm diam
9. Achenes more or less lenticular, thicker in the centre than at the margin, not twisted, 1.5-2 mm long; sepals 3 or 4; plants hairy	R. pumilio var. politus 9b.
9. Achenes strongly flattened, very thin, papery, with a thickened margin, often somewhat twisted when ripe, 2.5-4 mm long; sepals 3-5; plants almost glabrous	R. pentandrus var. pentandrus 8a.
8. Achenes with spines, tubercles and/or hairs on lateral faces
10. Plants slender; flowers inconspicuous, 2-6 mm diam.; torus glabrous; petals usually fewer than 5
11. Plants almost glabrous; achenes strongly flattened, very thin, papery, with a thickened margin, often somewhat twisted when ripe, 2.5-4 mm long, with small conical tubercles scattered over the central part of the faces, each terminated by a short recurred hair	R. pentandrus var. platycarpus 8b.
11. Plants hairy; achenes flattened but neither papery-thin nor twisted
12. Achenes 1.5-2 mm long; fruits often almost sessile
13. Basal leaves ternate, with linear to narrow-lanceolate leaflet-segments
14. Achenes more or less lenticular, their faces covered by hairs which sit on very short tubercles; sepals 5 R. pumilio var. purnilio 9a.
14. Achenes flat, with prominent conical tubercles scattered over the faces; sepals 3 or 4	R. sessiliflorus var. pilulifer 13b.
13. Basal leaves palmate to palmatifid, coarsely toothed or lobed	R. sessiliflorus var. sessiliflorus 13a.
12. Achenes 3-4 mm long; fruits mostly pedicellate
15. Achenes on lateral faces with long thin subulate tubercles (bristles), each terminated by a short recurved hair, stipitate at the base; sepals 3, spreading; petals 1-nerved, nerve sometimes forked towards the apex	R. hamatosetosus 1.
15. Achenes on lateral faces with short conical tubercles, each terminated by a recurved bristle, not or only shortly stipitate; sepals 4 or 5, reflexed; petals with 3 principal nerves, all once or twice forked in the lower half	R. parviflorus 7.
10. Plants robust, nearly glabrous; flowers conspicuous, 8-15 mm diam.; torus hairy; sepals reflexed; petals usually 5
16. Achenes 2-3 mm long, with short conical tubercles; basal leaves ternate, the middle leaflet longer stalked than the lateral leaflets	R. trilobus 14.
16. Achenes c. 7 mm long, with slender almost spiny tubercles; basal leaves roundish-cordate, 3-5-lobed	R. muricatus 4.

Author: Not yet available