The structural diversity of floral nectaries does not mean ontogenic diversity in Rhamnaceae species

•The floral nectary of different lineages of Rhamnaceae were described and compared.•Nectaries of Rhamnaceae have a great morphological diversity.•Floral nectaries originate from the hypanthium and are positioned above the ovary.•The two nectary types we found result of intercalary growth in the intrastaminal area.•The structural origin of nectaries in Rhamnaceae seems to be homologous.