Plants glabrous or sometimes pilose. Stems erect to decumbent or prostrate, not bulbous-based, without bulbils. Roots basal and sometimes also nodal, sometimes tuberous-thickened proximally. Leaves basal and cauline or all cauline; basal leaves when present similar to proximal cauline leaves; proximal cauline leaves petiolate, blades undivided, margins entire or finely toothed; distal cauline leaves simple, unlobed. Inflorescences 1-15(-40)-flowered cymes. Flowers pedicellate; sepals deciduous soon after anthesis, 3-5; petals yellow; nectary scale attached on 3 sides, forming pocket enclosing nectary, or sometimes projecting as free flap shorter than pocket, glabrous or ciliate, free margin entire or lobed; style present. Fruits achenes, 1-locular; achene body globose-lenticular to globose, 1-2 times as wide as thick, not prolonged beyond seed; achene wall thick, smooth, not ornamented (sometimes pubescent); margins low narrow ridge; beak much shorter than achene body.

Distribution

Widespread except lowland tropics.

Discussion

Species ca. 25 (10 in the flora).

The species of Ranunculus sect. Flammula are distinctive and easily recognized. Like many amphibious plants, however, they are very variable morphologically, and the species are difficult to define. The taxonomic status of the local endemic species recognized below should be reinvestigated. Depauperate plants of R. glaberrimus (R. sect. Epirotes) may have few or none of the leaves lobed. Such plants were formerly treated under the name R. oreogenes and referred to R. sect. Flammula. In the treatment of R. sect. Flammula below they will key to R. alismifolius var. alismellus, from which they differ in their usually ciliate nectary scales, larger sepals and petals, and larger heads of achenes.

The name Ranunculus lindheimeri Engelmann has been applied to specimens belonging to this section. The name has never been validly published, and its correct application is unclear.

Selected References

None.

Lower Taxa

Ranunculus alismifolius, Ranunculus ambigens, Ranunculus bonariensis, Ranunculus flammula, Ranunculus gormanii, Ranunculus hydrocharoides, Ranunculus laxicaulis, Ranunculus oresterus, Ranunculus populago, Ranunculus pusillus

Key

1	Petals 1-3, 1.5-2.5 mm.	> 2
1	Petals 4-12, 2-14 mm.	> 3
2	Bracts elliptic to ovate; achenes 1.4-1.8 mm; sepals 3.	Ranunculus bonariensis var. trisepalus
2	Bracts linear to lanceolate or oblanceolate; achenes 1-1.2 mm; sepals 4-5.	Ranunculus pusillus
3	Bases of roots conspicuously fusiform-thickened.	> 4
3	Bases of roots not thickened.	> 6
4	Stems prostrate, sometimes rooting nodally.	Ranunculus gormanii
4	Stems erect or ascending, not rooting nodally.	> 5
5	Bases of basal leaf blades acute.	Ranunculus alismifolius
5	Bases of basal leaf blades broadly obtuse to cordate.	Ranunculus populago
6	Achenes 0.8-1 mm; se United States.	Ranunculus laxicaulis
6	Achenes 1.2-2.8 mm; widespread.	> 7
7	Stems erect or ascending, not rooting nodally.	> 8
7	Stems erect or ascending to prostrate, rooting nodally.	> 9
8	Roots canescent; petals 4-6 mm.	Ranunculus oresterus
8	Roots glabrous; petals 5-14 mm.	Ranunculus alismifolius
9	Blades of well-developed leaves 5.9-12.2× 1.1-2.4 cm, acuminate at apex.	Ranunculus ambigens
9	Blades of well-developed leaves not as above, either 0.8-1.9(-2.7) cm long or 0.04-1 cm wide; acute or rounded to filiform at apex.	> 10
10	Leaf blades lanceolate to oblanceolate or filiform, base acute to filiform; beak of achene 0.1-0.6 mm; widespread.	Ranunculus flammula
10	Leaf blades ovate to broadly ovate, base rounded to weakly cordate; beak of achene 0.4-1 mm; desert southwest.	Ranunculus hydrocharoides