Description from Flora of China
Oldenlandia biflora Linnaeus, Sp. Pl. 1: 119. 1753; Hedyotis paniculata (Linnaeus) Lamarck; H. racemosa Lamarck; O. crassifolia Candolle; O. paniculata Linnaeus.
Herbs, annual or perennial, erect to procumbent, to 15(-30) cm tall; stems 4-angled to subterete and/or sulcate, glabrous. Leaves subsessile to petiolate; petiole to 0.5 cm, glabrous; blade drying papery to subleathery, elliptic-oblong, elliptic-ovate, obovate, oblanceolate, or elliptic, 1-4 × 0.3-1 mm, glabrous, base acute to obtuse then abruptly decurrent, apex acute to rounded; secondary veins indistinct; stipules fused to petioles, triangular, 1-2 mm, glabrous, usually costate, acute to long acuminate. Inflorescences terminal and in axils of uppermost leaves, cymose to compound-cymose, 1-6 cm, glabrous, 2-12-flowered, pedunculate; peduncles 0.5-3 cm; bracts triangular to lanceolate, 0.5-3 mm; pedicels 0.5-10 mm. Flowers subsessile to pedicellate, apparently distylous. Calyx glabrous; hypanthium portion turbinate, 0.5-1 mm; limb lobed essentially to base; lobes triangular, 0.3-1 mm. Corolla white, sometimes flushed with lavender, tubular to somewhat urceolate, outside glabrous or puberulent in lines; tube 1.2-2 mm, barbate in throat; lobes spatulate-oblong, 1-1.5 mm. Anthers included or exserted, 0.3-0.5 mm. Stigma exserted or apparently included, ca. 0.2 mm. Fruit capsular, subglobose, oblate, or hemispherical, 2.5-3 mm in diam., loculicidally dehiscent across top, beak 0.5-1 mm high, pedicels usually elongating; seeds numerous, black, foveolate. Fl. and fr. Jan-Sep.
The circumscription and name of this species is controversial or, at best, complicated. These are small herbs of ruderal sites and thus probably respond markedly to local conditions, in particular growing to a larger size with larger leaves, inflorescences, and fruit in sites with better conditions. Similar species that have been variously synonymized but are separated here include Hedyotis strigulosa and H. pterita; see further discussion under H. strigulosa. Alternatively Biju et al. (Rheedea 2(1): 11-18. 1992) separated H. biflora from H. racemosa (syn. Oldenlandia paniculata); their treatment is carefully done but regional, and because their key does not correspond well with the Chinese plants, their conclusions are not accepted here.
The name Oldenlandia crassifolia was placed in synonymy with both Hedyotis biflora and H. coreana (H. strigulosa) by W. C. Ko (in FRPS 71(1): 39, 77. 1999). The only other author who studied this name in any detail, Merrill (Enum. Philipp. Fl. Pl. 3(4): 492-512; 3(5): 513-576. 1923), cited this as a synonym of H. biflora and is followed here.
Limestone mountains, coastal areas, weedy fields, wastelands; sea level to 1200 m. Fujian, Guangdong, Guangxi, Hainan, Jiangsu, Taiwan, Yunnan [India, Indonesia, Malaysia, Nepal, Vietnam; SE Asia to Pacific islands].