So small and so rich: diversity of floral resources in miniature Oncidiinae (Orchidaceae) and their relation to pollinators.

- Oncidiinae is one of the most important subtribe among the Neotropical orchids, with an enormous diversity of floral morphology and secretory structures. This subtribe attracts a diverse array of pollinators which explore a variety of floral resources on its flowers. - In this paper we provide a detailed investigation of the floral anatomy of 32 species of micro Oncidiinae. We applied histochemical tests to all the studied species in order to determine the diversity of the glands and rewards. The diversity of secretory flower structures and rewards was related to the group of pollinators known for this orchid subtribe. - We verified that half of the species (16 species, 50%) secrete oil as a resource, being pollinated by female of solitary bees. Species of some distinct nectar secreting genera (four species, 12.5%) are pollinated by a range of nectar searching animals. Species of the genus Notylia (four species, 12.5%) release floral perfumes that reward male Euglossini bees. Most of the investigated species (six species, 18.75%) possess osmophores that are involved in pollinator attraction. Two species of Capanemia (6.25%) do not offer any floral reward, suggesting that pollination by food deception is involved. - There are strong variations in the anatomy of reward-producing structures and resources in Oncidiinae. The diversity of floral rewards affects the range of pollinators, which are related to the diversification of this subtribe throughout the Neotropics. The understanding of the relationships between Oncidiinae species and their pollinators is crucial to our knowledge of the evolution of pollination systems in the huge plant family represented by the orchids.