The flowers are diurnal, and white, pink, or purple and generally very hairy or fuzzy in the mouth of the corolla tube. They are apparently pollinated mainly by butterflies and hummingbirds. The flowers are distylous: some plants have only flowers of the long-styled ("pin" form), with the stigma positioned at the top of the corolla tube and the anthers positioned below, inside the tube; other plants have short-styled flowers ("thrum" form) with the reciprocal or opposite arrangement, with the anthers positioned at the top of the corolla tube and the stigmas below, inside the tube. This reciprocal arrangement is believed to promote out-crossing and diminish pollination by the same flower form, by depositing pollen on different parts of the pollinator so that the pollen from the short-styled flowers is transferred to the stigmas of the long-styled flowers, and vice versa. In general the distylous type of flower also has incompatibility at the cellular level, so the pollen of long-styled flowers generally has a very low success rate in other long-styled flowers, and vice versa.