Cotula flower head. Coloured scanning electron micrograph (SEM). Cotula is a genus of flowering plant in the sunflower family. It includes plants known generally as water buttons or buttonweeds. 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. Magnification: x15 when printed at 10 centimetres wide