Floral morphology and development of Epimedium pubescens and Plagiorhegma dubium (Berberidaceae) and their systematic significance

Epimedium and Plagiorhegma are the representatives of two early-diverging clades in Podophylloideae of Berberidaceae. Flowers are dimerous and trimerous respectively, but their floral development is little known. Here, we used scanning electron microscopy to clarify the structure and development of flower and inflorescence in Epimedium pubescens and Plagiorhegma dubium and compared these with other Berberidaceae to better understand floral evolution within the family. Our results show that the two genera share some significant features. The petal and stamen primordia emerge independently. The carpel is ascidiate from the earliest stages of development. The ovule is anatropous and bitegmic. However, E. pubescens has a paniculate inflorescence, while a lateral floral bud is initiated but aborted in P. dubium. In E. pubescens, both inner sepals and petals are delayed compared with other organs (vs. delay in petal development only for P. dubium). Petals of E. pubescens have a nectariferous spur (vs. no nectariferous tissue for P. dubium). The style of E. pubescens is long with a flat stigma (vs. short with trumpet-shaped stigma for P. dubium). These differences suggest that Epimedium and Plagiorhegma may not be closely related and support placing them separately in two clades of Podophylloideae, complementing results from molecular studies.