Ranunculus aquatilis diffusus
Buttercup family (Ranunculaceae)
This is a submerged aquatic plant up to 3' long that branches
occasionally. The stems are light green, terete, somewhat succulent,
and glabrous; sometimes the stems have vertical grooves that are fine
and shallow. At intervals along the entire length of each stem, there
are alternate leaves about ½–1½" long and similarly across. These
leaves consist of multi-branched filiform segments; they are medium
green or olive green, glabrous, and somewhat flexible to somewhat
stiff. The leaves are nearly sessile, or they have petioles up to ¾"
long. The petioles are light green and glabrous; they are surrounded by
tubular sheaths that often split open along one side. The sheaths are
translucent to reddish brown and usually glabrous, although sometimes
they are hairy. Emergent or floating leaves do not develop on this
variety (var. diffusus) of White Water Buttercup (Ranunculus
aquatilis). Across from the middle to upper leaves, emergent
flowers are produced on pedicels up to 3" long. Unlike the foliage, the
flowers are held up to 2" above the water surface. The pedicels are
light green to reddish brown, terete, relatively stout, and glabrous.
flower is ½–¾" across, consisting of 5 spreading white petals, 5 light
green to light yellow sepals, a yellowish or yellowish green head of
8-25 pistils, and several yellowish stamens surrounding the pistils.
The petals are oblanceolate to obovate in shape with rounded to nearly
truncate tips; the bases of these petals are usually yellow. The sepals
are lanceolate to broadly elliptic in shape; they are either widely
spreading (underneath the petals) or somewhat declined. The filaments
of the stamens are variable in length, even on the same flower. The
blooming period occurs primarily during the summer, lasting about 2-3
months. Afterwards, the pedicels of the flowers curve downward into the
water. The small seedheads are globoid-ovoid in shape and 4-5 mm. long. Individual seeds are about 1.5 mm. long, 1.0 mm.
across, and somewhat flattened; they can spread to new locations by
water currents or they are blown about by the wind on the water surface. At the
bottom of each plant, the root system is shallow and fibrous. When the
lower stem is decumbent on the water bottom, it can develop rootlets
near the axils of the leaves. This plant often forms colonies.
The preference is full sun, shallow clear water up to 2½' deep, and
bottom soil that is mucky, silty, or a mixture of sand and organic
material. This plant prefers bodies of water where there is an absence
of strong currents and where there is some protection from strong winds.
& Habitat: The native White Water Buttercup is
occasional in northern
Illinois, while in central and southern Illinois it is uncommon or
absent (see Distribution
Map). This map combines the distributions of
Ranunculus longirostris and Ranunculus
trichophyllus, as the latter two
species are considered synonyms of Ranunculus aquatilis
Water Buttercup (Ranunculus aquatilis) is widely
distributed in both
North America and Eurasia, where several varieties have been described.
Habitats of this plant include shallow ponds, streams with slow
currents, and deep ditches. White Water Buttercup can be found in both
high quality and disturbed wetlands.
Associations: The flowers are cross-pollinated
by bees, flies, and
beetles (especially Prasocuris spp.). Both nectar
and pollen are
available as floral rewards; the beetles may also gnaw destructively on
the flowers. Even though the foliage is somewhat toxic, some vertebrate animals make limited use of water
buttercups as a source of food. The foliage and/or seeds of these
aquatic plants are eaten by the Trumpeter Swan, Wood Duck,
Muskrat, Snapping Turtle, and Blanding's Turtle (Bellrose, 1942/1976;
Martin et al., 1951/1961; Lagler, 1943). The finely divided leaves
provide cover for aquatic insects and other small invertebrates.
A pond at a city park in Lake County, Illinois, and indoors.
Another common name is White Water Crowfoot. When this aquatic plant
occurs in colonies, it is capable of a showy display because of its
emergent flowers. It is similar in appearance to another aquatic plant,
Ranunculus flabellaris (Yellow Water Buttercup),
except the latter
species has yellow flowers. In North America, there are at least two
varieties of White Water Buttercup: Ranunculus aquatilis
Ranunculus aquatilis diffusus. The typical variety
is found in western
North America and it has both submerged and floating leaves. The
variety that is described here (var. diffusus) is
found in eastern
North America and it has only submerged leaves. Some authorities, e.g.,
Mohlenbrock (2014) and the USDA Plants website, divide Ranunculus
aquatilis diffusus into two species, Ranunculus
Ranunculus longirostris. The former species is
supposed to have achenes
with shorter beaks and flexible leaves with longer petioles, while
the latter species is supposed to have achenes with longer beaks and
stiff leaves with shorter petioles. However, other authorities believe
these characteristics freely intergrade in the field and they are
influenced by environmental conditions (eFloras website, New England
Wildflower Society website). Thus, according to them, White Water
Buttercup in Illinois should be referred to as Ranunculus aquatilis
latter viewpoint has been adopted here.