Development of carpels and ovules in Dialypetalanthus fuscescens Kuhlm. [Rubiaceae] : an enigmatic taxon

Abstract

Dialypetalanthus is a monospecifi c genus that occurs in the Amazon Basin of Brazil, Bolivia and Peru and occupies a controversial position among the Rubiaceae. We continue this taxonomic discussion with the overall aim of clarifying the systematic position of D. fuscescens within the Rubiaceae. To accomplish this, we analyzed the ontogeny of its gynoecium, in particular the fl oral meristem, as well as the development of the carpels and cauline placentation. Gynosporogenesis and the diff erentiation of the carpellary septa and ovules were also described. Dialypetalanthus fuscescens was classifi ed according to evolutionary diagrams found in the literature. Th e following characteristics were observed in D. fuscescens: 1) permanence of the fl oral meristem in the central basal part of the early fl ower bud; 2) dual origin of carpellary septum; 3) trizonate ovular primordia with only one fertile gynospore per ovule; and 4) cellular proliferation in the chalazal region. Embryological results confi rm the classifi cation of D. fuscescens in the subfamily Ixoroideae. Th ese results are distinct from any others previously proposed in the evolutionary diagram. Th erefore, we conclude that this study has presented evidence strongly suggesting that Dialypetalanthus possesses new morphological-type of ovule we refer to as the Dialypetalanthus-type.