Know Your Natives – Stalked Wild Petunia

Stalked Wild Petunia (Ruellia pedunculata ssp. pedunculata*) of the Acanthus (Acanthaceae) family has flowers with large, showy, trumpet-shaped, purplish corollas, similar to those of the unrelated Garden Petunia**. The genus name honors Jean de la Ruelle (1474-1537), a French herbalist. The specific epithet, from the Latin, refers to the prominent peduncles or flower stalks. In the U.S., the species is widespread in eastern Texas and Oklahoma, southeast Missouri, far-south Illinois, Arkansas and Louisiana, with rare occurrences from Mississippi to Georgia. In Arkansas, plants occur statewide (except for lowlands along the Mississippi River), favoring open woodlands, wood borders, and glades, on dry to mesic soils.

Photo 1: Flowers are trumpet-shaped with five flared lobes. Narrow-leaved plant in background is Evening Rain Lily (Cooperia drummondii). Photo – May 3.

Roots of a mature plant consist of a shallow, elongate rootstock with numerous, radiating, semi-succulent roots that may be a foot long. Rootstocks produce a single stem that includes below-surface nodes. At the end of the growing season, the entire stem dies back to the main rootstock, to be replaced by new stems the following year. Rootstock and roots are yellowish tan.

Photo 2: Remnants of previous years’ stems are indicated by arrows. A white bud on the main rootstock would have produced a stem in the new growth year. Entire plant is shown in Photo 4. Photo – July 16.

This herbaceous perennial, with opposite, decussate leaf pairs, grows to a height of about 1½ feet. Plants have a single main stem, with lateral, ascending, typically flowering stems growing from the leaf axils. Floral branches may be from < ¼ inch to 2 inches long, the length decreasing distally. Spacing of leaf pairs along stems may be to 2-3 inches, while spacing along branches is tighter. The pale green to reddish stems are covered evenly by short, soft to somewhat stiff hairs with the longest hairs below the swollen leaf nodes.

Leaves are dark green above and lighter below, with entire (uncut), slightly undulating margins. Small basal leaves may be ovate; larger leaves are ovate-elliptic to elliptic, to lanceolate on smaller plants. Largest stem leaves, 2¾+ inches long (including a ⅛-inch petiole) and 1⅛+ inches wide, occur at and just above mid-stem. The significantly smaller branch leaves are to 1⅛ inches long (including a ⅛-inch petiole) and ½ inch wide. Upper and lower leaf surfaces are evenly short pubescent, feeling downy to slightly rough. Venation is pinnate.

Photo 3: This 1⅛-inch first-year plant has pubescent, ovate leaves. Leaves occur in opposite, decussate pairs. This plant’s four roots were 2 inches long. Photo – July 12.
Photo 4: This 20-inch tall plant exhibits characteristic short floral branches along several straight stems. Note immature seed capsules. Photo – July 16.
Photo 5: Leaf shape varies from oval to ovate-elliptic to lanceolate. Upper leaf surfaces shown on left and lower leaf surfaces on right. Leaf margins are uncut to slightly undulating. Photo – June 19.
Photo 6: Leaves of this opposite leaf pair each subtend floral branches (arrows). The swollen node has longer hairs extending from petioles. At the node, stem is ⅛ inch wide and branches are 1/32 inch wide. Photo – July 17.

A floral branch terminates with an apical bud set between a pair of opposite leaves, each leaf with an axillary bud. The apical bud may develop into a single flower subtended by a leaf pair or it may remain vegetative and extend the branch’s length. Lateral buds may develop into secondary floral branches with their own terminal flower and pair of bracteal leaves. Axillary buds of leaf pairs at the ends of branches may not develop fully or may remain dormant.

Photo 7: This floral branch (yellow arrow) has an unopened terminal flower (red arrow) which is subtended by a pair of bracteal leaves. Subtending leaves of this terminal flower also subtend two secondary axillary branches (white arrows), which, in turn, bear a pair of bracteal leaves and a flower bud. Photo – June 24.

Flowering is mostly from late May into June. The large, rather delicate, nearly actinomorphic flowers, to 2+ inches long and 1+ inches wide, have a tubular corolla with 5 widely spreading, broad, rounded lobes attached to a flaring throat. The corolla and throat are a uniform lavender color with main veins, especially of the lower lobe, often highlighted in dark lavender. The narrow, white tube is subtended by a stubby calyx (with five ½-inch-long linear, bristle-like lobes) atop an ⅛ inch pedicel. Pedicel and exterior of calyx are finely pubescent.

Flowers have 4 white stamens (filament + anther) and one pistil (green ovary + white style + white stigma). Stamens, adnate to the floral tube, are in two pairs, of which one is slightly shorter. Anthers are positioned at the rim of the throat. The flattened stigma, positioned above the throat, has a short one-sided “arm” that extends toward center of throat. The corollas last up to a day before dropping off (with stamens attached). The thread-like style persists for a short time.

Photo 8: These flowers, on secondary branches, have dark lavender veins on lower corolla lobe. The white, delicate, angled, single-arm stigmas are positioned above the throat. Photo – May 28.
Photo 9: Five corolla lobes have about the same shape. Four white stamens are in two pairs, the filaments adnate below to the floral tube. This corolla lacks dark lavender veins on the lower lobe. Photo – June 24.
Photo 10: Corollas have lavender throats and lobes and white tubes. Flowers are subtended by variously sized opposite leaf pairs, as can be seen below the fruit (on right, brown) and spent flower (lower right). Photo – June 24.
Photo 11: The soft to hirsute pubescence of straight hairs can be seen on the branch, leaves, calyx lobes, and along the creases of the corolla. Photo – Jun 19.
Photo 12: Flowers have four stamens (in two pairs, adnate to the corolla tube) and a style with an arm-like stigma (see Photo 8). Lowermost lobe is at upper right. Tube is 1 inch long. Lobes are ½ inch long. Photo – June 24.

With fertilization, pale green, elongate, hardened capsules form, extending well beyond the calyx lobes, to about ¾ inch long and ⅛ inch wide. Capsules ripen to a light brown; calyxes remain green. Capsules contain about 10 round seeds stacked in two rows, each held by a pair of claw-like umbilical structures that wrap along the seed’s lower edge. The mature thick-walled capsules, which may remain closed for a month or more, disperse seed by dehiscing kinetically along two sutures extending from apex to base. Seeds are covered with minute, twisty lines of papillae which extend away from the hilum.

Photo 13: Developing fruits, surrounded by 5 linear calyx lobes, are uniformly puberulent. Pedicels are short. Photo – July 13.
Photo 14: Capsules contain flat, round seeds on a pair of placentas. Claw-like umbilical structures wrap along edge of seeds, near the hilum. Photo – July 19.
Photo 15: The round flat seeds are covered with minute papillae. Upper seed retains its umbilical structure. Squares are ¼ inch. Photo – July 25.

With its large flowers and open growth habit, a robust specimen plant would be of interest in a sunny to partially shaded, well drained garden. However, often plants seem to stay small and spread aggressively by seed. With below surface stem-buds and dormant rootstock-buds, manual removal of plants would require removal of the entire main rootstock. With these considerations, this species is probably best suited for a wild garden or natural area. It survives droughts very well.

In addition to Stalked Wild Petunia, three other native species occur in Arkansas: Carolina Wild Petunia (Ruellia caroliniensis), Hairy Wild Petunia (Ruellia humilis), and Smooth Wild Petunia (Ruellia strepens), all with similar lavender flowers. Stalked Wild Petunia can be identified by its uniform short pubescence and presence of floral branches. The other three species have clusters of flowers growing directly from axils of stem leaves.

* Two subspecies have been identified (sometimes they are elevated to species): Ruellia pedunculata ssp. pedunculata and R. pedunculata ssp. pinetorum. Ruellia pedunculata ssp. pedunculata has puberulent ovaries. Ruellia pedunculata ssp. pinetorum, occurring in dry to wet pine woodlands of the Gulf Coastal states and South Carolina, has glabrous or glabrate ovaries. The former occurs on dry slopes and in dry glades and woodlands.

** Petunia x atkinsiana is the classification assigned to all hybrids within the Garden Petunia complex, such as, Petunia axillaris, Petunia integrifolia and Petunia inflata. All Garden Petunias are in the Nightshade (Solanaceae) family.

Article and photographs by ANPS member Sid Vogelpohl

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