A morphological and anatomical description of the floral syndrome ofNierembergia is given, including a survey of the presence of elaiophores in most of its species, chromatography of the floral oils and observations on the pollinator behaviour. The principal pollinators areTapinotaspis spp. includingT. chalybaea which is endowed with oil collectors on the middle legs. Other exomalopsines (Lanthanomelissa andParatetrapedia) and centridines (Centris) also visitNierembergia for pollen and oil. Based on these observations and on a morphological study of the fertile parts, different pollination modes are recognized and the biogeography and evolution of the genus is discussed.