Herbs, perennial; caudex herbaceous or woody, herbage tending to dry black. Stems prostrate, ascending, erect, or spreading, glabrous. Leaves cauline, opposite; petiole present; blade not fleshy, not leathery, margins weakly or sharply serrate. Inflorescences axillary, flowers solitary; bracts present. Pedicels present; bracteoles smaller than calyx lobes, not surrounding calyx of flowers they subtend. Flowers bisexual; sepals 5, proximally connate, calyx bilaterally symmetric, campanulate, lobes ovate, outer lobes ± as wide as inner; corolla white or lemon yellow with purple or reddish veins in throat, bilaterally symmetric, weakly bilabiate, campanulate [salverform], tube base not spurred or gibbous, throat not densely pilose internally, lobes 5, abaxial 3, adaxial 2, abaxial lip projecting to spreading; stamens 4, medially or distally adnate to corolla, didynamous, filaments glabrous; staminode 0; ovary 2-locular, placentation axile; stigma 2-lobed. Fruits capsules, dehiscence septicidal, slightly loculicidal at apex. Seeds 40–80, black or brown, angled, wings absent. × = 11.

Distribution

c, e United States, Mexico, Central America, South America, introduced in Asia (India, Sri Lanka), Africa (Cameroon, Sierra Leone), Australia.

Discussion

Species ca. 10 (2 in the flora).

Selected References

None.

Lower Taxa

Mecardonia acuminata, Mecardonia procumbens

Key

1	Stems erect; leaf blade margins weakly serrate; corollas white with purple veins in throats, adaxial lobes connate 1/2–2/3 lengths; seeds: radial walls of reticulum smooth.	Mecardonia acuminata
1	Stems spreading, prostrate, or ascending; leaf blade margins sharply serrate; corollas lemon yellow with reddish veins in throats, adaxial lobes connate nearly to apices; seeds: radial walls of reticulum mamillate.	Mecardonia procumbens