Description: This native perennial plant is about 1½–3' tall, branching occasionally. The stems are green, angular, and hairless. The opposite leaves are up to 6" long and 3½" across; they are ovate-lanceolate, smooth or slightly undulate along their margins, and mostly or entirely hairless. These leaves have short petioles.
From the axils of the upper leaves, there
develops 1-3 funnelform flowers on short pedicels. Each flower is up to 2" long
and 2" across; the corolla is narrowly tubular at the base, but it spreads
outward into 5 rounded lobes. The color of this corolla is usually lavender or
pale purplish pink; plants with white corollas also occur. The lobes of the
corolla have undulate edges and a delicate appearance. At the throat of the
corolla, is a slender white style and several stamens. Along the lower corolla,
there are several slender lines that are purple; they function as nectar guides
for visiting insects. At the base of the flower, there is a hairy green calyx
that consists of 5 lanceolate sepals; these sepals are united at the base and
they are shorter than the corolla. The blooming period occurs during the summer
for 2-3 months. Each diurnal flower lasts only a single day; a single mature
plant will have about 0-2 flowers in bloom during a typical summer day. Each
flower is replaced by an oblongoid seed capsule that is 2-celled and contains
several seeds. Some plants produce insignificant cleistogamous
flowers.
Cultivation: The preference
is light shade or partial sun, moist to mesic conditions, and a fertile loamy
soil with abundant organic material. This plant is not often bothered by
disease and insects. It may fail to flower in areas with medium to dense
shade.
Range & Habitat: Smooth
Wild Petunia occurs occasionally in southern and central Illinois; it is absent
in northern Illinois. Habitats include moist to mesic open woodlands, woodland
edges, areas along woodland paths, thickets, and thinly wooded slopes along
rivers. In woodlands where there is an absence of fire or other disturbance,
the population of this plant may decline because of excessive shade,
particularly when those woodlands have become dominated by Sugar Maple and
various Honeysuckle shrubs.
Faunal
Associations: The flowers have few visitors, although their nectar
and pollen occasionally attract long-tongued bees. Robertson (1929) observed
the Digger bee, Synhalonia speciosa, visiting the flowers of Smooth Wild
Petunia. Sometimes pieces of the corolla are used by Megachile spp.
(Large Leaf-Cutting Bees) in their brood nests; these bees may also visit the
flowers for nectar and pollen. The caterpillars of the butterfly Junonia
coenia (Buckeye) have been observed feeding on the foliage of Ruellia
spp. Otherwise, little is known about floral-faunal relationships for
plants in this genus.
Photographic
Location: Along a path in a mesic area of Busey Woods, Urbana,
Illinois.
Comments: The flowers of
Ruellia spp. (Wild Petunias) have a striking resemblance to the flowers
of the cultivated Petunia, which has been introduced from South America and
belongs to a different family of plants. However, the flowers of Wild Petunias
have less diversity of color. There are several Ruellia spp. in
Illinois; some of these are restricted to the southern third of the state.
Smooth Wild Petunia is the least hairy of these species as its foliage is
hairless or sparingly hairy; only its sepals are reliably hairy. The species
Ruellia humilis (Hairy Wild Petunia) is a prairie wildflower that
prefers sunny dry habitats. It is a shorter and much hairier plant. Two
woodland species, Ruellia caroliniensis (Carolina Wild Petunia) and
Ruellia pedunculata (Stalked Wild Petunia), also have hairier foliage
and their sepals are linear (less than 1/8" across). Smooth Wild Petunia has
lanceolate sepals that exceed 1/8" across. Often, its nearly sessile flowers
are partially hidden by the foliage.