Ranunculus aquatilis var. diffusus
Ranunculus subg. Batrachium
thread-leaf white water buttercup, water buttercup, white water butter cup
nodal, never tuberous.
creeping or floating, not bulbous-based, without bulbils.
all filiform-dissected.
cauline, either simple and laminate (with expanded blade), or completely dissected into filiform segments, or with proximal leaves filiform-dissected and distal leaves laminate; laminate leaves petiolate, undivided or 3-parted, segments entire to shallowly cleft and crenate;
filiform-dissected leaves petiolate or sessile.
axillary, solitary flowers.
pedicellate;
sepals deciduous soon after anthesis, 5;
petals 5, white or white with yellow claws;
nectary scale attached on 3 sides, forming ridge or shallow pocket not covering nectary, glabrous, free margin entire;
style present.
achenes, 1-locular;
achene body ellipsoid or flattened-ellipsoid, 1-2 times as wide as thick, not prolonged beyond seed;
wall thick, with coarse transverse ridges;
margin low narrow ridge;
beak much shorter than achene body.
1-1.8 × 0.8-1.2 mm;
beak 0.2-1.2 mm.
= 16, 32, 48.
Ranunculus aquatilis var. diffusus
Ranunculus subg. Batrachium
Populations of Ranunculus aquatilis var. diffusus with long achene beaks are not known from the Old World. In North America, beak length varies continuously over the whole range given for the variety, and separation of plants with unusually long beaks as R. longirostris is not tenable. Ranunculus aquatilis var. diffusus shows geographic variation, and some regional forms have been recognized as separate varieties. Dwarf creeping arctic plants may be called R. aquatilis var. eradicatum, plants with sparsely pubescent or glabrous receptacle from eastern North America may be called R. aquatilis var. calvescens, plants with linear, noncapillary leaf segments from the northern Great Basin may be called R. aquatilis var. porteri, and very robust plants from Oregon and northernmost California may be called R. aquatilis var. harrisii. Extreme forms of these races are recognizable, but they intergrade and many specimens cannot be confidently assigned to one or another of them.
The Eurasian species Ranunculus circinatus Sibthorp has been reported from North America. These reports are based on specimens of R. aquatilis var. diffusus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species ca. 15 (3 in the flora).
Unlike most species of Ranunculus, members of this subgenus are not poisonous.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaves all dissected into filiform segments. | R. aquatilis var. diffusus |
1. Leaves not all filiform-dissected, all or some laminate and shallowly to deeply 3-lobed or -parted. | → 2 |
2. Leaves all laminate, margins shallowly crenate-lobulate, segments rounded; e North America. | R. hederaceus |
2. Leaves of 2 types: laminate and filiform-dissected (filiform-dissected leaves sometimes few and inconspicuous in R. lobbii); laminate leaves 3-parted, segments elliptic, obovate, or fan-shaped; w North America. | → 3 |
3. Receptacle glabrous; style 1–1.5 mm. | R. lobbii |
3. Receptacle hispid; style 0.1–0.8 mm. | R. aquatilis var. aquatilis |
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