Plants

Plant Deception

Angiosperms, commonly referred to as flowering plants, are the most diverse group of land plants, with over 350,000 species occupying nearly every habitat on Earth. Roughly 7,500 are pollinated through deceit and, of these, approximately 6,500 are in the orchid family (Orchidaceae). Although deceptive flowers suffer reduced pollination success compared with rewarding species, deception remains common, and recent phylogenetic evidence has suggested that deception may even be ancestral in orchids or have evolved early in their history. One hypothesis to explain the evolution and maintenance of deception in plants is that they are able to utilize the resources that would be allocated for nectar production in other aspects of their survival, such as overall growth. Another more empirically well-supported hypothesis is that their deception encourages cross-pollination.

Increasing the likelihood of cross-pollination is beneficial because self-pollination has a negative impact on fitness and can cause reduced genetic variation or even inbreeding depression. Orchids are especially susceptible to losing reproductive opportunities because their pollen is typically packed into masses called pollinia, which can be removed by a pollinator in a single visit, thus rendering self-pollination problematic. This might explain why deception is so prominent in orchids; nearly one-third of orchids offer no rewards.

Although it has not been well established, it is assumed that pollinators' visits to deceptive flowers will be brief and few. Whereas pollinators typically visit many flowers on the same rewarding plant, they are less likely to investigate multiple flowers on a deceptive plant, reducing the likelihood of pollinator-mediated self-pollination.

These nonrewarding plants most commonly use food deception by resembling rewarding species either generally or specifically. Another relatively common method is sexual deception, a system in which plants mimic the females of pollinator species in order to attract males. Other forms of deception present in some species are less common and have received less empirical support. They include the use of brood-site or shelter imitation, in which plants attract pollinators seeking oviposition sites or refuge; “pseudoantagonism,” in which plants exploit the territorial behavior of some pollinator species; and “rendezvous attraction,” in which plants resemble and grow near rewarding plants, and are pollinated by males searching the flowers for foraging females.

Food Deception

The vast majority of deceptive plants engage in food deception to attract pollinators. Some species in the arum (Araceae) and birthwort (Aristolochiaceae) families, among others, exploit carrion flies and beetles looking for food by resembling carrion. Some plants that have male and female flowers deceive pollinators because the male flowers offer rewards and the female flowers do not. Examples of this can be found in the palm (Arecaceae), aster (Asteraceae), and gourd (Cucurbitaceae) families. However, most plants utilize what is known as “generalized food deception,” resembling the general features of a rewarding flower without a specific model.

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