1. Mikania cordifolia (Linnaeus f.) Willdenow, Sp. Pl. 3: 1746. 1803.
Cacalia cordifolia Linnaeus f., Suppl. Pl., 351. 1782
Stems 6-angled, gray-tomentulose or tomentose; internodes 5–20 cm. Petioles 25–55 mm, densely pilose to tomentose. Leaf blades ovate to deltate, 5–10 × 3–8 cm, bases cordate, margins subentire to undulate-dentate, apices acute to acuminate, faces densely pilose to tomentose (abaxial paler than adaxial). Arrays of heads compound-corymbiform (terminal and lateral), 6 × 7+ cm. Heads 7–10 mm. Phyllaries substramineous, elliptic to narrowly ovate, 6–8 mm, apices acute to slightly rounded. Corollas white, 3.5–5 mm, lobes linear. Cypselae brown, 3–4 mm, glabrous or pubescent, sparsely gland-dotted; pappi of ca. 60 white, barbellate bristles 4–5 mm. 2n = 38.
Flowering Sep–Dec. Wet areas, woodlands, calcareous soils; 0–100 m; Ala., Fla., Ga., La., Miss., Tex.; Mexico; West Indies; Central America; South America.
Mikania cordifolia grows in all wet-tropical and subtropical America from northern Argentina to the lower Gulf Coastal Plain of the United States. It has the largest natural distribution of any species in the genus. In the tropics, M. cordifolia tends to be weedy, frequently occupying disturbed sites, usually in the lowlands. It is not weedy in the United States. In Louisiana, Mississippi, and Texas, M. cordifolia occurs in relatively open seeps and stream sides in beech (Fagus grandiflora Ehrhart) woods. It was collected in 1875 from the Navy Ballast Yard in Kargins Point, New Jersey (W. C. Holmes 1981); no further records for New Jersey are known.