Floral development of Gymnospermium microrrhynchum (Berberidaceae) and its systematic significance in the Nandinoideae

•Floral organogenesis of Gymnospermium was studied under the SEM.•The pattern of floral organogenesis of Gymnospermium was directly verified.•The floral ontogenetic data are phylogenetically informative.•Gymnospermium and Leontice was recognized as separate genera.

Morphological and molecular analyses of the Berberidaceae have recognized the Nandinoideae clade of four genera: Caulophyllum, Gymnospermium, Leontice, and Nandina. However, generic relationships of the Nandinoideae remain to be explicitly defined with morphological characteristics. In this study we examined the floral ontogeny of Gymnospermium to gain new insights into the evolution of floral structures in the family and generic relationships of the Nandinoideae. The inflorescence of Gymnospermium is racemose with bracts and floral primordia initiated acropetally. Floral parts form in the order of sepal, stamen, staminode, and carpel. Both sepals and stamens are initiated in three series and each series has two sepals/stamens. Stamen and staminode share a common primordium with the former initiated earlier than the latter. In the Berberidaceae the floral trimery is an ancestral trait, while dimery and its variant (such as non-whorled dimery in Gymnospermium) are a derived feature. The non-whorled pattern of the initiation of sepals and stamens and their dimery provide synapomorphies for the close relationship of Gymnspermium and Leontice in the Nandinoideae.