XVI International Botanical Congess

Of the 21 genera hitherto proposed by various authors only four are presently accepted by the IOS Working Party: Pereskiopsis Britton & Rose, Pterocactus K. Schum., Tacinga Britton & Rose and Opuntia Mill. Apart from Quiabentia which is referred to Pereskiopsis, all remaining genera are assigned to Opuntia. Primarily based on seed morphological and anatomical characters but also including vegetative, floral, fruit morphological, and palynological characters a narrower, but well-founded generic concept of Opuntioideae is suggested here. Analysis of all available data has shown that 13 of the 21 genera of hitherto proposed can be clearly circumscribed. These are - apart from those already accepted by the IOS Working Party -Airampoa, Austrocylindropuntia, Brasiliopuntia, Consolea, Cylindropuntia, Maihueniopsis, Miqueliopuntia, Nopalea, Quiabentia, and Tephrocactus. Seed characters of high taxonomic significance are the morphological and anatomical structure of the funicular aril (funicular envelope), the shape of the embryo and the relative size of the perisperm.