INDUCED homeotic floral mutants in Arabidopsis thaliana and Antirrhinum majus1-3 are used to investigate the molecular mechanisms that establish floral organ identity. Here we describe bicalyx, a naturally occurring homeotic floral variant in Clarkia concinna (Onagraceae) that replaces petals with sepal-like structures. Typical C. concinna flowers have four sepals, four tri-lobed, bright pink petals, four stamens and a four-part ovary. Bicalyx flowers appear to have eight sepals, no petals and wild-type stamens and ovary with no reduction in fertility. All bicalyx organs on a plant are alike and have no developmental abnormalities, in contrast to many of the homeotic phenotypes described4-7. Bicalyx demonstrates that a large morphological difference governed by a simple genetic change can become established in a natural plant population and suggests that even homeotic genes play a role in the evolution of morphological diversity in plants.