Floral morphology and morphogenesis of <i>Davidia</i> and <i>Nyssa</i> (Nyssaceae, Cornales), with special emphasis on their reproductive systems

Abstract Nyssaceae is a family belonging to Cornales which is sister to Mastixiaceae. The floral development of Davidia involucrata and Nyssa sinensis is investigated using scanning electron microscopy to compare the floral ontogenesis among the genera of Nyssaceae and to evaluate the systematic importance of the floral features in Cornales. Davidia is bisexual with two kinds of floral units: staminate and bisexual, the latter with many staminate flowers and a central hermaphroditic flower. The merism of flowers is variable in both types of floral units. Young carpels are initiated independently from each other but become confluent by basal growth. Each carpel has a single ovule, which is unitegmic, hemitropous, and initially exposed. Nyssa sinensis is dioecious, and both staminate and carpellate reproductive units are closed and umbellate. The organ number is variable in staminate flowers but stable in carpellate flowers. There are occasional staminodes in carpellate flowers. Like in Davidia, the ovary is inferior with axile placentation and one hemitropous ovule in each locule. Davidia, Nyssa, and Camptotheca share reproductive units with an extremely shortened axis, complex breeding systems, decurrent stigmas, and hemitropous ovules. Diplostemonous stamens are also present in Mastixiaceae, which is a potential synapomorphy of the Nyssaceae-Mastixiaceae clade.