The floral biology ofNuphar lutea subsp.macrophylla, native to Central Texas, has been investigated. The flowers are protogynous with anthesis occurring over a period of several days. Flowers are visited by a number of insects but are effectively pollinated by the beetleDonacia piscatrix Lac., which spends its entire life history in association withNuphar. Evidence is assembled which suggests that the overall floral structure together with the sequence of floral development and the timing of sepal movements (i.e., the opening and closure of the flower) are primary adaptations to assure beetle pollination.