1. Wollastonia biflora (Linnaeus) Candolle, Prodr. 5: 546. 1836.
孪花菊 luan hua ju
Verbesina biflora Linnaeus, Sp. Pl., ed. 2, 2: 1272. 1763; Acmella biflora (Linnaeus) Sprengel; Melanthera biflora (Linnaeus) Wild; M. biflora var. ryukyuensis (H. Koyama) K. Ohashi & H. Ohashi; Stemmodontia biflora (Linnaeus) W. Wight; Wedelia biflora (Linnaeus) Candolle; W. biflora var. ryukyuensis H. Koyama; W. wallichii Lessing var. megalantha H. Chuang; Wollastonia scabriuscula Candolle ex Decaisne, nom. illeg. superfl.
Subshrubs or somewhat woody herbs. Stems elongate, branched, scandent, coarsely appressed strigose. Cauline leaves long petiolate; petiole 1.2-2.3 cm; blade ovate, 7-14 × 3-8 cm, thickly papery, appressed strigose, base rounded, margin serrate, apex acuminate. Capitula (1 or)3-6, terminal, 2-3 cm wide; peduncles 1.5-5.5(-8) cm, slender or thick; involucre 10-13 × 5-7 mm; phyllaries ovate-lanceolate or narrowly ovate, densely appressed strigose, gradually narrowed to tip. Ray florets 14 or 15, yellow, 1-seriate; corolla 9-13 mm, 2- or 3-dentate. Disk florets yellow; corolla ca. 5 mm, apex 5-lobed. Achenes 3-3.5 × 2-2.5 mm, cuneate at base, often 3-angled, coarsely strigose toward tip; pappus bristles 2 or 3, 2-2.5 mm, sometimes absent. Fl. year-round. 2n = 30, 45, 50, 75.
Seasides. Guangdong, Guangxi, Guizhou, Hainan, Hubei, Hunan, Jiangxi, Sichuan, Taiwan, Xizang, Yunnan [India, Indonesia, Japan, Malaysia, Philippines, Vietnam; Pacific islands].
Under Wedelia biflora the variety W. biflora var. ryukyuensis was recognized by Koyama (Acta Phytotax. Geobot. 33: 245. 1982), differing from the typical variety by degree, in having larger capitula with more ray and disk florets, larger leaf blade with a longer petiole, and a chromosome number of 2n = 45 (see also C. I Peng et al., Fl. Taiwan, ed. 2, 4: 1093-1094. 1998). However, in their recent synopsis of the genus, Wagner and Robinson (Brittonia 53: 539-561. 2001) recognized only a variable species without infraspecific taxa.