Cotula nigellifolia

Cotula is a genus of flowering plant in the sunflower family. It includes plants known generally as water buttons or buttonweeds. The species within this genus can vary extensively in their habit, leaf division, involucre, receptacle and achenes. This makes it difficult to define them by comparing their morphology. The genus can only be defined by looking at the corollas of their flowers. Most are disciform (lacking ray florets). These corollas may be tubular, reduced or even absent. Another characteristic is their solitary heads growing on a peduncle.