Ruellia humilis Nutt., low ruellia, prairie–petunia. Perennial herb, not rosetted, several–stemmed at base, with only 1 axillary shoot per node, in range to 60 cm tall; shoots with only cauline leaves, with long and short pilose hairs.
Stems 4–sided but bulbous pulvinus at base of each internode, to 5 mm diameter (mid–internode) and to 7 mm (bulbous base), internodes to 115 mm long, with a pair of channeled faces and a pair of flat faces, old stems becoming cylindric with projecting leaf bases, short–pilose and pilose, puberulent on pulvinus, flat faces with minute streaks.
Leaves opposite decussate, simple, short–petiolate fused across node as 2 ledges, without stipules; petiole hemi–cylindric to flattened top–to–bottom, 1—6 × 1.5—2.8 mm, glabrous; blade ovate, 18—90 × 7.5—60 mm, tapered to broadly tapered at base, entire or subentire (low teeth) and often long–ciliate on margins, broadly acute to obtuse at tip, pinnately veined with principal veins somewhat raised on upper surface and raised on lower surface, upper surface pilose and on midrib also short–hairy, lower pilose hairs along veins.
Inflorescence dichasial cyme, on short axillary shoot, 2 cymes per node among foliage, 1–flowered or 3–flowered, bracteate; peduncle to 3 mm long; bracts (bractlets) 2 and opposite at top of peduncle, leaflike, elliptic, 20—25 × 7—8 mm; pedicel 1 mm long.
Flower bisexual, radial, ca. 30 mm across; calyx 5–lobed, 16—20 mm long, green; tube bell–shaped, 1.5—2 × 1.5 mm; lobes subequal, linear, 10—18 mm long, outer (lower) surface conspicuously hirsute–ciliate and having long–stalked glandular hairs with reddish heads approaching tip, inner (upper) surface short–pilose; corolla 5–lobed, in bud 5–pleated and white, densely short–pilose; tube ca. 25 × 2—2.5 mm, slightly enlarged and glabrous around ovary, 10–ribbed, short–pilose with downward–pointing hairs from below midpoint; throat funnel–shaped, ca. 15 × 15 mm, with 5 raised principal veins each giving rise to 2 raised lateral veins, short–pilose; lobes widely spreading, obovate, ca. 12 × 12 mm, light violet, lacking visible or raised veins, lower surface short–pilose; stamens 4, of 2 lengths, fused to top of corolla tube in pairs of 1 long and 1 shorter; filaments fused portion winglike and 1 mm long, free portions 4 and 5 mm long, white; anthers dorsifixed, dithecal, 1.8—2 mm long, white, longitudinally dehiscent; pollen white; pistil 1; ovary superior, ± spindle–shaped, ca. 1.2 × 0.4 mm, glossy green and glabrous, 2–chambered, each chamber with 2 ovules; style cylindric, 30+ mm long, white, with ascending short hairs to midpoint, stigma flattened.
Fruit capsule, loculicidal, dehiscent splitting nearly to base, 2–valved, mostly 8—10–seeded, club–shaped (obovoid), in range 12.5—16 × 3.5—4 mm, valves diverging ca. 60°, puberulent; calyx with long linear lobes and hirsute–ciliate; style at tip to 45 mm long.
Seed disc–like circular and flattened, 2.8—3.2 × 2.6—2.9 × 0.6—1 mm, brown, thickened on portion with seed chamber and other half winglike including a colorless margin.
A. C. Gibson