Protocarnivorous Plant - Defining Carnivory

Defining Carnivory

Debate about what criteria a plant must meet to be considered carnivorous has yielded two proposed definitions: one with strict requirements and the other less restrictive.

The strict definition requires that a plant must possess morphological adaptations that attract prey through scent or visual cues, capture and retain prey (i.e. the waxy scales of Brocchinia reducta or downward facing hairs of Heliamphora prevent escape), digest the dead prey through enzymes produced by the plant, and absorb the products of digestion through specialized structures. The presence of commensals is also listed as strong evidence of a long evolutionary history of carnivory. By this definition, many sun pitcher plants (Heliamphora) and the cobra lily (Darlingtonia californica) would not be included on a roster of carnivorous plants because they rely on symbiotic bacteria and other organisms to produce the necessary proteolytic enzymes.

The broader definition differs mainly in including plants that do not produce their own digestive enzymes but rely on internal food webs or microbes to digest prey, such as Darlingtonia and some species of Heliamphora. Both the strict and broad definitions incorporate requirements for adaptations or resource allocations that result in the active attraction, capture, and/or digestion of prey. Both also require adsorption of the digested nutrients. The broader definition stipulates that the plant must receive some noticeable benefit from the carnivorous syndrome. That is, the plant must display some significant increase in fitness because of the nutrients obtained from its carnivorous adaptations (i.e. increased growth rate, increased chance of survival, higher pollen production or seed set).