沼生金纽扣 zhao sheng jin niu kou

Spilanthes uliginosa Swartz, Prodr. 110. 1788; S. iabadicensis A. H. Moore.

Herbs, annual, 10-30(-50) cm tall. Stems solitary or several from base, erect to ascending or occasionally decumbent, green to purple, glabrous to moderately pilose. Petiole 0.5-1.5 cm, sparsely to moderately pilose, wingless or narrowly winged; leaf blade lanceolate, narrowly ovate to ovate, 1.3-5 × 0.3-2.5 cm, glabrous to sparsely pilose on both surfaces, base attenuate to cuneate, margin sinuate to dentate, sparsely ciliate, apex acute to acuminate. Capitula radiate, solitary or 2 or 3, terminal, ovoid, 5-8 × 4-6 mm; peduncles 1.2-3 cm, sparsely pilose; receptacle 3-6 × 0.5-1 mm; paleae straw-colored or sometimes with purple tinge early in flowering, 2.5-3.5 × ca. 0.5 mm. Ray florets 4-7; corollas yellow to orange-yellow, 1.5-3.5 mm, tube 0.5-1.5 mm, lamina 3-toothed, 1-2 × 0.5-1.5 mm. Disk florets 68-148, yellow to orange-yellow, 4-merous; corollas 1-1.6 mm, tube 0.2-0.5 mm, throat 0.7-1.2 mm, lobes triangular, 0.2-0.3 × ca. 0.2 mm. Achenes black, 1.2-1.8 mm, moderately to densely ciliate with straight-tipped hairs; pappus of 2 subequal or unequal bristles, longer one 0.2-0.7 mm, shorter one 0.1-0.5 mm. Fl. year-round. 2n = 52.

Naturalized in Hong Kong and Taiwan [native throughout the tropics in Africa, America, and Asia; naturalized in the Pacific islands].