Vanilla flowers: much more than food-deception

In many flowering plants the attraction of pollinators is related to some kind of deception. Pollination by food-deception occurs in several angiosperm groups and is particularly widespread in orchids. Despite the apparent evolutionary success of pollination by food-deception, food-deceptive orchids show a low level of fruit set. Although studies are scarce, the pollination of Vanilla has been usually associated with nectar-deception. In Vanilla spp. (Vanilla bahiana, V. bicolor, V. chamissonis, V. edwallii, V. hartii, V. phaeantha, V. paulista, V. planifolia, V. ribeiroi and V. pompona), understanding the factors associated with pollinators is essential, since in vanilla production a cumbersome process of supplementary manual pollination is necessary to increase fruit set, which is frequently low under natural conditions. The production of floral rewards was investigated here in ten Neotropical Vanilla spp. based on morpho-anatomy and histochemical analyses of flowers. Six species (Vanilla bahiana, Vanilla bicolor, Vanilla chamissonis, Vanilla hartii, Vanilla phaeantha and Vanilla pompona) offer nectar as a reward. In Vanilla ribeiroi, the long trichomes of the labellum base are rich in starch grains and proteins, characteristic of food-hairs. The only secretory structures of Vanilla edwallii are osmophores on the inner surface of the labellum that are related to the attraction of oil-collecting bees as pollinators. Vanilla spp. possess sepaline and labellar osmophores. Inside the labellum the osmophores are arranged along longitudinal lines and act as resource guides. Although it is widely known that Vanilla flowers attract pollinators by nectar deception, the present data reveal that there may be a lack of knowledge regarding pollination in this group since the offer of nectar appears to be a common condition, at least for the euglossine-pollinated Neotropical clade. The remaining Neotropical groups exhibit other pollination strategies, such as the production of food-hairs and fragrances that attract oil-collecting bees to the flowers. The study of Vanilla pollination is extremely important because the need for manual pollination, added to the ripening and curing time, causes vanilla to be one of the most expensive spices in the world. According to the data presented here, the pollination systems of vanilla are much more diverse than classical food deception.

Automated summary

Deception is common in attracting pollinators in flowering plants, with food-deceptive pollination being widespread in orchids. Despite its evolutionary success, food-deceptive orchids have low fruit set levels. Understanding pollination factors in Vanilla species is crucial due to the need for manual pollination to increase fruit set.