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A morphological and anatomical description of the floral syndrome of Nierembergia 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 are Tapinotaspis spp. including T. chalybaea which is endowed with oil collectors on the middle legs. Other exomalopsines ( Lanthanomelissa and Paratetrapedia) and centridines ( Centris) also visit Nierembergia 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. [ABSTRACT FROM AUTHOR]

Plant species that secrete oil as their primary floral reward are rare and sporadically found in the angiosperms. We report here that Monttea, a genus previously unsuspected of being an oil-plant, produces lipids from trichome elaiophores on the inside of the lower (anterior) lip. The discovery of the production of oils by species of this S. American genus explains the occurrence of unusual dual-function collecting structures in Argentine Centris ( Hymenoptera: Anthophoridae) and explains the presence of oil-collecting bees in regions where oil-secreting flowers were previously thought to be absent. The behavior of these centridine pollinators on Monttea flowers parallels that of oil-collecting bees on Diascia ( Scrophulariaceae) in S. Africa. [ABSTRACT FROM AUTHOR]