Flowers of annonaceae: Morphology, classification, and evolution

The present paper describes the diversity in floral characters of Annonaceae and their distribution over the family, and discusses their value for classification and generic delimitation. Flower morphology predominated historical classifications of this family since Hooker & Thomson (1855) introduced floral characters to divide the Asiatic genera into a number of tribes. Since then, several taxonomists presented a classification of the Annonaceae using floral characters, which classifications, however, are generally felt as unnatural. A survey of the flower morphology of all genera reveals a reticulate distribution of floral character states. Classification of the genera, as presented in this study, learns that floral characters different from those in previous classifications should be used if one aims at a better correlation with non-floral features. The chromosome number in this respect turned out to be an important character. Classification of the neotropical genera is relatively easy compared with classification of the African and Asiatic genera. Current genus delimitations in many cases are disputable. The functional aspects of the flower morphology are discussed in connection with a literature survey of the results from field studies on flower biology of Annonaceae. Some remarks on evolutionary aspects are added.