New World Tropical
Acmella oleracea (L.) R.K. Jansen
A. repens (Walter) Rich. Ex Pers.
introduced to Asia, Africa, Australia, Pacific Islands
prostrate or erect herbs
Annual or perennial. Stem prostrate to erect. Leaves opposite, decussate; leaf blade lanceolate to ovate, sparsely hairy; apex round to acute; base round to attenuate; margin entire to toothed. Inflorescence terminal, a solitary head or a few heads in cymes; radiate or discoid. Involucre ± hemispheric; phyllaries 1-3-seriate, subequal or outer longer, entire or irregularly dentate; receptacle conical; paleate. Ray florets, when present, 2-3-lobed; pistillate; typically yellow to orange. Disk florets of 4-5 triangular, yellow or orange lobes.
riparian, flood zones on river banks, pond edges, and in wet ditches
A genus of 30 species. The species Acmella repens (Walter) Rich. ex Pers. is semi-aquatic to aquatic, typically with floating stems; also known as Acmella oppositifolia var. repens (Walter) R.K.Jansen.