17. Clarkella J. D. Hooker, Fl. Brit. India. 3: 46. 1880.
岩上珠属 yan shang zhu shu
Authors: Tao Chen & Charlotte M. Taylor
Small herbs from tubers, apparently perennial, unarmed, usually with a cluster of prophylls at stem base. Raphides present. Leaves opposite, isophyllous or sometimes markedly anisophyllous at basalmost node, without domatia; stipules persistent, interpetiolar and fused to petioles, triangular, perhaps sometimes glandular on margins. Inflorescences terminal, cymose, umbelliform, or subfasciculate, few to several flowered, pedunculate or sessile and tripartite, bracteate. Flowers pedicellate, bisexual with biology unknown. Calyx limb well developed, markedly reticulate veined, 5(-7)-lobed for ca. 1/2 length. Corolla white, slenderly salverform or funnelform-salverform, glabrous inside; lobes 5, valvate in bud. Stamens 5, inserted at base of corolla tube, included; filaments short. Ovary 2-celled, ovules numerous in each cell on axile placentas inserted not far below middle of septum; disk pilosulous; stigma 2-lobed, pubescent. Fruit indehiscent, obconical, dry, with funnelform calyx limb persistent; seeds numerous, small, subellipsoid, black papillose or -granular.
One species: China, N India, N Myanmar, Thailand.
This is a poorly known species or genus that apparently prefers wet limestone substrates and is similar to Pseudopyxis.