Ranunculus sceleratus L. var. sceleratus, celery–leaf buttercup, blister buttercup, cursed crowfoot. Aquatic annual, taprooted and fibrous–rooted, rosetted, 1–stemmed at base, with ascending lateral branches from each node, ascending to suberect, in range to 50 cm tall; shoots with basal leaves and cauline leaves, 3–lobed, glabrate with soft hairs in inflorescence; taproot slender to thicker and fleshy, adventitious roots dense on lower 10 mm of stem.
Stems ± cylindric with subtle, broad ridges, to 15 mm diameter, with rounded ridges descending from each leaf, glossy green, internodes to 80 mm long, smooth, glabrous; internodes wide–hollow, nodes solid.
Leaves helically alternate, deeply 3(5)–lobed, petiolate, with stipules; stipules 2, = wide–membranous wings along petiole, to 17 mm long, to 1.6 mm wide, narrower on cauline leaves; petiole flared at base above hemi–cylindric concave on upper side from base and broadly channeled above, < 30—115 mm long, rounded on lower side, somewhat compressed top–to–bottom, with sparse, long, soft hairs within broad channel; blades to 65 × 20—95 mm, length < width, of basal and floating leaves, semi–circular to kidney–shaped in outline, cordate at base, palmately veined with principal veins scarcely sunken on upper surface and raised on lower surface, lobes wedge–shaped or fan–shaped to obovate or elongate–rhombic, terminal lobe symmetric and 15—60 × to 30 mm, lateral lobes asymmetric and wider, each lobe with several rounded sublobes and broad teeth above midpoint (terminal lobe) or base–to–top on outer margin (lateral lobe), with a purple gland and margin on each sublobe or tooth; blade of upper cauline leaf 3–lobed, decreasing upward with only short teeth or entire, oblong to elliptic lobes.
Inflorescence cymelike, terminal for each principal shoot, on robust shoot 3–forked at node having diverging axes and a central pedicellate flower, diverging axes somewhat unequal (of different ages) at each fork and with decreasing internodes, bracteate; bract subtending each axis 1—3–lobed, cauline leaflike and entire, the lowest to 25 × 7 mm decreasing upward, green, 3–veined or 1–veined, with inconspicuous silky hairs, having a pair of membranous stipules at base attached to short petiole, stipules acuminate or ovate, to 4 mm long; pedicel at anthesis upright, ridged, 5—11 mm long increasing 3× in fruit, light green, glabrous, lacking pulvinus at base.
Flower bisexual, radial, 6—7.5 mm across; receptacle conic, having stiff hairs to 0.4 mm long; sepals (3—)5, reflexed, cupped oblong–obovate, in range ca. 2—2.5 × 1.6 mm increasing to 3.5 mm long in fruit, green with colorless margins, silky pubescent on outer (lower) surface; petals typically 5, obovate, ca. 3.5 × 1.6 mm, glossy yellow on upper surface with projection 0.4 mm long and nectary at base; stamens helically alternate, 10 fertile in 2 series, lacking staminodes; filament 1.5—2.4 mm long, greenish; anthers basifixed, dithecal, 0.8—0.9 mm long, light yellow, with sacs produced on sides of connective, longitudinally dehiscent; pollen light yellow; pistils helically alternate, ca. 200, tightly arranged on receptacle in range to 7.5 × 4.5 mm; ovary ± D–shaped to asymmetrically ovate in outline compressed side–to–side, ca. 1 mm long, green, with depression on each face below midpoint, glabrous, 1–chambered with 1 ovule; style absent; stigma oriented to outer side, green, papillate.
Fruits achenes, helically alternate, in a dense, oblong–cylindric to ellipsoid cluster (3—)4.5—10 × (5—)7.5—13 mm; achene broadly elliptic in outline to D–shaped, compressed side–to–side, 1—1.2 × 0.8—1.2 × 0.4—0.5 mm, minutely bumpy (tuberculate) or forming widely transverse wrinkles, glabrous; beak ± absent (minute stigma), with oblique scar close to base.
A. C. Gibson