Description from Flora of China
Petrodoxa J. Anthony; Slackia Griffith.
Herbs, rarely subshrubs, perennial, epipetric or terrestrial, rhizomatous, stemless or simple stemmed. Leaves many, basal or on stem, equal to subequal in a pair; leaf blade strigose to villous or glabrescent, base cordate to cuneate. Inflorescences often umbel-like, lax, axillary, 1- to few-flowered cymes; bracts 2, opposite. Calyx actinomorphic, 5-sect from base; segments equal. Corolla blue-purple to red, zygomorphic, inside glabrous, outside oblique, campanulate, not swollen, shorter than to nearly equalling limb, 3-9 mm in diam.; limb 2-lipped; adaxial lip 2-lobed, distinctly shorter than abaxial lip; abaxial lip 3-lobed, lobes equal or central lobe longer, apex rounded to obtuse. Stamens 4, adnate to corolla near or slightly above base, included; anthers basifixed, all 4 coherent together, thecae subparallel, slightly divergent at base, confluent at apex, dehiscing poricidally; connective not projecting; staminode 1 or absent, adnate to adaxial side of corolla tube. Disc ringlike or inconspicuous. Ovary ovoid, 1-loculed; placentas 2, parietal, projecting inward, 2-cleft. Stigma 1, terminal, capitate, undivided. Capsule oblique in relation to pedicel, narrowly ovoid to very narrowly oblong, much longer than calyx, dehiscing loculicidally to base; valves 2, straight, not twisted. Seeds unappendaged.
About seven species: China, Myanmar, N Vietnam; five species in China.