Floral morphology and relationships of Clusia gundlachii with a discussion of floral organ identity and diversity in the genus Clusia

The genus Clusia L. is highly variable in many floral features. Several Clusia species have floral organs of mixed or uncertain identity, such as organs that are transitional between bracteoles and sepals, petaloid sepals, and partly petaloid stamen rings. Unique in Clusia is the "corona" of Clusia gundlachii Stahl, a thick, urn-shaped structure that is initiated as a ring primordium. In male flowers it surrounds a synandrium, and in female flowers it surrounds the ovary and a row of staminodes. The corona combines features typical of both petals and stamens of other Clusia species. It is hypothesized that this corona may be the result of the altered expression patterns of the genes that determine floral organ identity. Clusia gundlachii has many floral features in common with two small genera that are sometimes included in Clusia: Havetiopsis and Oedematopus. These genera have four thick connivent petals. Their apparent close relationship makes it seem likely that the corona of C. gundlachii evolved via congenital fusion of such petals. The corona is also somewhat similar to the staminodial rings present in many Clusia species, but taxa in which such organs occur show little similarity to C. gundlachii in terms of other floral characters.