Description from Flora of China
Annuals, 2-62 cm. Stems erect. Leaves cauline, opposite, petiolate; blade lanceolate to broadly ovate, surfaces glabrate to densely pilose, 3-veined, margin entire or serrulate to serrate. Synflorescence cymose. Capitula radiate or discoid; involucres hemispheric to campanulate, 2.5-6 mm in diam.; phyllaries persistent or deciduous, 6-9[-16], in 2[or 3] series, elliptic, ovate-lanceolate, oblong, or ovate, outer shorter, herbaceous or scarious, margin entire or minutely laciniate; receptacles conical, paleaceous, paleae persistent or deciduous, scarious, proximal broadly elliptic to obovate, often connate at bases or nearly to apices, united in groups of 2 or 3 to adjacent proximal phyllary, each complex often enclosing and shed with a ray achene, distal persistent or deciduous, lanceolate to obovate, entire or 2- or 3-lobed, convex to conduplicate. Ray florets [0-](3-)5(-8)[-15], female, fertile; corollas white or dull white to pinkish [or purplish], tubes pilose, lamina quadrate-obovate to oblong, lobes 0-3. Disk florets 5-50[-150], bisexual, fertile; corollas yellow, tubes shorter than cylindric throats, pilose, 5-lobed, deltate; anthers yellow; style branch apices acute. Achenes obconical to obpyramidal, glabrous or strigose, ray achenes often shed with subtending phyllary plus 2 or 3 adjacent paleae; pappus absent or of (1-)14-20 white or gray, persistent, fimbriate, sometimes aristate, scales. x = 8.
See Canne, Rhodora 79: 319-389. 1977.
About 15-33 species: Caribbean to Bermuda, Central, North, and South America; two species (both introduced) in China.