Ranunculus pusillus
Ranunculus aquatilis
low buttercup, low spearwort, weak buttercup
renoncule aquatique, water buttercup, water crowfoot, white water butter cup, white water crowfoot, white water crowsfoot, white western buttercup
not thickened basally, glabrous.
erect or ascending, rooting at most proximal nodes, glabrous.
glabrous.
laminate and filiform-dissected; laminate leaf blades reniform, 3-parted, 0.4-1.1 × 0.7-2.3 cm, segments obovate or fan-shaped, shallowly cleft, margins crenate;
filiform-dissected leaves with stipules gradually tapering upward, connate for their whole length.
ovate or lanceolate, 1.2-4.2 × 0.5-1.2 cm, base acute to truncate, margins entire or denticulate, apex acuminate to rounded.
bracts linear to lanceolate or oblanceolate.
receptacle glabrous;
sepals 4-5, spreading or reflexed from base, 1.5-3 × 1-1.5 mm, glabrous or sparsely hirsute;
petals 1-3, 1.5-2 × 0.5-1 mm;
nectary scales glabrous.
receptacle hispid, rarely glabrous;
sepals spreading or reflexed, 2-4 × 1-2 mm, glabrous;
petals 5, 4-7 × 1-5 mm;
style 0.1-0.8 mm.
usually recurved.
hemispheric to cylindric, 2-8 × 2-3 mm;
achenes 1-1.2 × 0.6-0.8 mm, ± tuberculate, glabrous;
beak absent or nearly so, to 0.1 mm.
hemispheric to ovoid, 2-4 × 2-5 mm;
achenes 1-2 × 0.8-1.4 mm, glabrous or hispid;
beak persistent, filiform, 0.1-1.2 mm.
Ranunculus pusillus
Ranunculus aquatilis
In most specimens of Ranunculus pusillus, the heads of achenes are hemispheric to short-ovate and only 2-3 mm. Occasional plants with cylindric heads of achenes 4-6 mm from the Gulf Coast states have been called R. pusillus var. angustifolius.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Varieties 2 (2 in the flora).
Ranunculus aquatilis is very variable. In the past it has often been treated as three or four species and many varieties. These segregate taxa have been based on the size, petiolation and rigidity of the leaves (now known to be primarily under environmental control), petal size and curvature of the fruiting pedicel (both sometimes variable along single stem), and number of achenes per head and length of achene beak (which vary continuously and are not correlated with one another). Unless reliable characters can be found, only two of the taxa recognized in older floras can be maintained.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaves of 2 types: laminate and filiform-dissected; w North America. | var. aquatilis |
1. Leaves all filiform-dissected; widespread. | var. diffusus |
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PNW Herbaria, Turner Photog. 
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