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Species Spotlight: Wild Petunia (Ruellia humilis)

Updated: Jan 5, 2023

Lance-leaf Coreopsis flowers

Interesting facts:

  • The genus name honors Jean de la Ruelle (1474-1537), a French herbalist and physician.

  • The Ruellia family contains about 2500 species worldwide that range from herbs to shrubs and small trees. Most are tropical.

  • The common name Wild Petunia comes from the resemblance to the garden petunia (completely unrelated).

Native Environment/Plant Information:

Wild Petunia is a clump-forming rhizomatous plant about one foot tall. Over time, a single plant will produce a clump 1 to 2 feet in diameter. It can become weedy given the right conditions. The root system is fibrous and rhizomatous, often forming colonies of clonal plants. Stems are generally hairy, unbranched and range from 6 to 12 inches tall. The hairy leaves, which measure up to 2.5 inches long and 1 inch wide, are generally opposite and attached directly to the stem without a stalk (sessile) or with a short stalk (subsessile). Flowers are produced in small clusters at the leaf axils. Flowers are 1-2 inches across, tubular and 2-3 inches long. They are generally lavender or light purple and have prominent “bee guidelines” in the center of the flower. These bee guidelines are fine purple lines radiating from the center and serve as a nectar guide to visiting pollinators. Wild Petunias flower one-by-one over many months between June and September. Each individual flower typically opens during the morning and falls off by evening. The dark seeds produced are fairly large and generally fall to the ground around the parent plant.

Wild Petunia prefers full sun and well-drained, dry sites. Wild Petunia is most frequently found in areas with poor soil and sparse vegetative cover, or in other disturbed areas with richer soil. Its most common habitats include dry or sand prairies, fields, meadows, and open upland woodlands. They also perform well on limestone glades, bluffs, sandy cemeteries, sand flats, and areas along roadsides and railroads.

Wild Petunia plant with lighter flower color.

Cultural Information:

Wild Petunia is easy to grow and quite adaptable. It tolerates full or partial sun, moist to dry conditions, and practically any kind of soil. It struggles to compete with taller, more aggressive species under moist conditions with rich soil. It does best in poor sandy or rocky soils with good drainage. Wild Petunia is tolerant of heat, humidity and drought.

Wild Petunia can freely self-seed. Deadheading spent flower stalks will encourage continued blooming and can prevent any unwanted self-seeding. The clump will slowly expand from the center outward.

Wild Petunia flowers have a unique appearance reminiscent of garden petunias. It's an attractive plant. Wild Petunia is grown occasionally in flower gardens, particularly along borders, or in rock gardens because of its large and abundant flowers. It functions best in Rock Gardens, Native Gardens, Wild Gardens and Prairies where it is forced to compete against taller species.

Close up of fading flower showing color variation.

Wildlife uses:

Wild Petunia attracts a variety of butterflies, bees, and other pollinators. Long-tongued bees are the most important pollinators, including Anthophorid bees (Anthophora spp.) and Leaf-cutting bees (Megachile spp.). Short-tongued bees and Syrphid flies also visit flowers, but they are not effective pollinators and mainly collect stray pollen. The light color and funnel-like shape of the diurnal flowers suggest that they may be visited by day-flying Sphinx moths and Hummingbird moths. It has been reported that the caterpillars of the Buckeye Butterfly (Junonia coenia) may feed on the foliage of Ruellia spp. occasionally.

Useful Links and References:

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