This is widespread in thin woods and glades from Central America to southeastern states (but rarely north of the Ohio Rv.), on damp or dry sites. It is generally absent from calcareous soils in Ky. Differences in ecology from triglomerata are not clear, but oligantha tends to occur in more shady habitats, on average. In addition to the distinctive tubercles below its achenes, oligantha has lateral spikes on relatively long-arching, filiform, reddish peduncles, dilated toward the summit (FNA 23, W). Lateral peduncles of triglomerata (and nitida) tend to be more erect, though becoming pendulous in deep shade. Stems of oligantha are often pubescent; those of triglomerata are usually glabrous, or distally somewhat scabrous.