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Ranunculus
See list of 20 species in this genusPhylogeny and morphology support a division of a broadly defined Ranunculus (Emadzade et al. 2010). In New England, the genera Coptidium and Ficaria are segregated from the remainder of Ranunculus. Reports of the European Ranunculus circinatus Sibth. (e.g., Graves et al. 1910) were based on collections of R. aquatilis var. diffusus. Ranunculus laxicaulis (Torr. & Gray) Darby was reported from CT by Dowhan (1979), but the specimens are referable to R. ambigens. Ranunculus laxicaulis was also reported from VT by Magee and Ahles (1999), but specimens are unknown (and were likely misidentified). References: Duncan (1980), Whittemore (1997).
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1a. Plants aquatic, with submersed leaf blades that are finely divided into narrow segments less than 1 mm wide (the emersed leaves, if present, with broader segments) [Fig. 817]
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2a. Petals white with yellow bases [Fig. 817]; leaf segments capillary; achenes coarsely wrinkled on the surface, with a beak 0.2–0.5 mm long
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2b. Petals yellow; leaf segments flat; achenes smooth on the surface, with a beak 0.4–1.8 mm long
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3a. Petals 7–12 mm long; achenes 1.8–2.2 mm long, the lower portion thickened and spongy; achene beak 1–1.8 mm long; styles 0.8–1.2 mm long (in part)
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3b. Petals 3–7 mm long; achenes 1–1.6 mm long, not thickened in the lower half; achene beak 0.4–0.8 mm long; styles 0.2–0.4 mm long (in part)
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1b. Plants terrestrial, of wetlands, or sometimes aquatic, with leaf blades that are simple or divided with relatively broad segments [Figs. 815,819,820]
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4a. All the leaf blades simple and unlobed [Fig. 820]
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5a. Leaf blades cordate to reniform [Fig. 820]; achenes with longitudinal nerves
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5b. Leaf blades linear to lanceolate; achenes without longitudinal nerves
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6a. Leaf blades 0.4–8 mm wide; plants with filiform, arching stolons; petals 1–5 mm long; achenes essentially smooth
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6b. Lower leaf blades (6–) 8–24 mm wide; plants lacking stolons, though rooting at the base of the stem; petals 5–8 mm long; achenes reticulate-patterned
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4b. Either the lower leaf blades or those borne on the stem or both conspicuously lobed to compound [Figs. 815,819]
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7a. Leaves dimorphic—the basal ones simple with ovate to reniform blades and borne on elongate petioles, the stem ones becoming with conspicuously lobed blades and becoming sessile upward; nectary scale fused to petals on 3 sides, forming a pocket that encloses the nectary
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8a. Petals 6–8 mm long; achenes 1.8–2.2 mm long
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8b. Petals 1–3.5 mm long; achenes 1.1–2 mm long
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9a. Stems villous, the hairs usually discernable to the naked eye; base of some roots tuberous-thickened and 1–2 mm thick; basal leaf blades usually broad-cuneate to truncate at base; receptacle glabrous
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9b. Stems glabrous (infrequently with some tiny, sparse hairs that can be seen with magnification); none of the roots tuberous-thickened, the base 0.2–1.5 mm thick; basal leaf blades usually cordate to subcordate at base; receptacle sparsely pubescent
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10a. Beak of achene 0.6–1 mm long, strongly curved [Fig. 816]; sepals pubescent on abaxial surface
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10b. Beak of achene 0.1–0.2 mm long, straight to barely curved; sepals glabrous on abaxial surface
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7b. Leaves ± monomorphic, relatively similar in general pattern, gradually becoming smaller upward, with shorter sinuses, and/or with shorter petioles; nectary scale separate from petal for at least 50% of its length and forming a flap over the nectary or the scale poorly developed and forming a crescent-shaped to circular ridge that surrounds but does not cover the nectary
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11a. At least the larger leaves with definite, unwinged petiolules (i.e., these leaves compound) [Fig. 819]
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12a. Petals 2–5 mm long, as long as or shorter than the sepals; anthers up to 1 mm long
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12b. Petals 6–15 mm long, usually longer than the sepals; anthers 1.2 mm long or longer
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13a. Sepals reflexed along a defined, transverse fold 2–3 mm above the base [Fig. 818]; plants either perennial with stems bulbous-thickened at base or annual
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14a. Achene faces smooth; petals 9–13 mm long; plants perennial, with stems bulbous-thickened at base
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14b. Achene faces usually sparsely papillose (rarely smooth); petals 7–10 mm long; plants annual, without bulbous-thickened stems (in part)
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13b. Sepals spreading (sometimes reflexed from the very base in age); plants perennial, the stems not thickened at the base
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15a. Some roots tuberous-thickened, the others slender; petals usually widest at or below middle; stems erect to ascending, not rooting at the nodes
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15b. Roots all slender; petals usually widest distal to the middle; stems decumbent to creeping and often rooting at the nodes (or upright and not rooting in R. hispidus)
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16a. Styles short, curved, the persistent stigma spread out over upper side of style; achene beak (0.7–) 0.8–1.2 (–1.4) mm long
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16b. Styles elongate, with a terminal, deciduous stigma; achene beak (0.8–) 1.5–2.6 (–3) mm long
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17a. Stems spreading to procumbent, 50–80 (–91) cm long at anthesis, sometimes rooting at the nodes; plants of hydric soils (e.g., swamps, marshes, ditches)
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17b. Stems upright, 14–45 (–60) cm tall at anthesis, never rooting at the nodes; plants of mesic to dry-mesic, upland woodlands and forests
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11b. Leaves with flattened, winged, sometimes ill-defined petiolules (i.e., the leaves lobed but not compound) [Fig. 815]
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18a. Stems floating or prostrate and rooting at the nodes; achenes plump, without a sharp or wing-like keel
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19a. Petals 7–12 mm long; achenes 1.8–2.2 mm long, the lower portion thickened and spongy; achene beak 1–1.8 mm long; styles 0.8–1.2 mm long (in part)
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19b. Petals 3–7 mm long; achenes 1–1.6 mm long, not thickened in the lower half; achene beak 0.4–0.8 mm long; styles 0.2–0.4 mm long (in part)
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18b. Stems erect, rooting at only the base; achenes flattened, with a sharp or wing-like keel between the faces
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20a. Achene faces usually sparsely papillose (rarely smooth); sepals reflexed along a defined, transverse fold 2–3 mm above the base; plants annual (in part)
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20b. Achene faces smooth; sepals spreading or reflexed from the very base; plants perennial from rhizomes, caudices, or bulbous bases or annual in R. sceleratus
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21a. Petals 7–11 (–15) mm long, longer than the sepals; sepals spreading; receptacle glabrous; achenes 2–3 ×1.8–2.4 mm
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21b. Petals 2–5 mm long, equal to or shorter than sepals; sepals reflexed from near the base (sometimes spreading in R. sceleratus); receptacle pubescent (sometimes glabrous in R. sceleratus); achenes 1–2.2 ×0.8–1.8 mm
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22a. Anthers up to 1 mm long; style absent; achenes in a cylindric cluster, each with a very short, straight beak ca. 0.1 mm long; stems not thickened at the base; nectary scale forming a crescent-shaped to circular ridge that surrounds but does not cover the nectary
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22b. Anthers longer than 1 mm; style present; achenes in a spherical cluster, each with a hooked beak 1–1.4 mm long; stems bulbous-thickened at the base; nectary scale forming a flap over the nectary
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Each photo represents one species in this genus.