Ranunculus sect. Echinella
Prodr. 1: 41. 1824.
Plants pubescent or glabrous. Stems erect or decumbent, not bulbous-based, without bulbils. Roots basal, never tuberous. Leaves basal and cauline or sometimes only cauline; basal and lower cauline leaves similar, petiolate, blades undivided, lobed, or compound, segments lobed or unlobed, margins entire or dentate. Inflorescences 2-16-flowered cymes (cymes sometimes sympodial, then flowers seemingly inserted opposite bracts). Flowers pedicellate (sessile in R. platensis); sepals deciduous soon after anthesis, 5 (3 in R. platensis); petals yellow (sometimes absent in R. hebecarpus); nectary scale attached basally, free from petal for at least 1/2 its length, forming flap covering nectary, glabrous, free margin entire; style present. Fruits achenes, 1-locular; achene body discoid, strongly flattened, 3-7 times as wide as thick, not prolonged beyond seed; wall thick, spiny, tuberculate, or papillose (sometimes smooth in R. sardous); margin low or high, broad or narrow ridge; beak much shorter than achene body.
Worldwide except lowland tropics.
Species ca. 15 (8 in the flora).
|1||Petals 1–2 mm; achenes finely papillose, papillae terminating in slender hooked hairs or spines; native or introduced.||> 2|
|1||Petals 4–10 mm; achenes coarsely papillose, tuberculate, or spinose, rarely smooth; introduced weeds.||> 4|
|2||Flowers sessile; sepals 3.||Ranunculus platensis|
|2||Flowers pedicellate; sepals 5.||> 3|
|3||Achenes ornamented on faces and margin, with lanceolate beaks; native of Pacific Slope.||Ranunculus hebecarpus|
|3||Achenes ornamented on faces but not margin, with deltate beaks; introduced weed, widespread in North America.||Ranunculus parviflorus|
|4||Sepals spreading; achenes 5–9 in single whorl, the faces and margin long-spinose.||Ranunculus arvensis|
|4||Sepals reflexed; achenes 10–60 in ovoid or globose heads, the faces papillose to spinose or rarely smooth, margin smooth.||> 5|
|5||Basal leaves compound; achene beak 0.3–0.7 mm.||> 6|
|5||Basal leaves simple; achene beak 1–2.5 mm.||> 7|
|6||Achene faces sparsely papillate or sometimes smooth; petals more than 5 mm.||Ranunculus sardous|
|6||Achene faces densely tuberculate; petals less than 5mm.||Ranunculus trilobus|
|7||Achene faces but not margin covered with long spines; beaks 2– 2.5 mm.||Ranunculus muricatus|
|7||Achene faces but not margin covered with high sharp tubercles or low spines; beaks ca. 1 mm.||Ranunculus marginatus|