Table 1 A list of the plant behavioral examples provided in the questionnaire where respondents were asked to rank on a scale from one to four (or six) whether they considered the presented behavior to be intelligent or not (1 = not intelligent to 4 or 6 = very intelligent)

(1) Habituation in Mimosa pudica L

 Habituation is a decreased response of an individual to a stimulus that is being presented repeatedly (your response to a new sound diminishes as you become accustomed to it; traffic, for instance). Can plants become accustomed to a repeated stimulus? Mimosa pudica L. (the sensitive plant) is well known for quickly folding its leaves in response to touch. It is possible that Mimosa exemplars stop folding their leaves after being exposed to frequently repeated stimuli. Gagliano et al. [15] studied habituation in Mimosa by repeatedly dropping potted individuals from a certain height. As they reported, the plants in effect stopped folding after a number of drops. The experiment discarded the alternative hypothesis that the leaves had stopped folding due, for instance, to motor fatigue after the continuous drops, and not to habituation. Intriguingly, this learned response persisted, lasting up to a month [15]

(2) Conditioned learning in Pisum sativum L

 In Pavlov’s classical conditioned learning, Pavlov was able to show that a trained dog was able to salivate with just a neutral cue (a bell as the conditioned stimulus) in the absence of its food (the unconditioned stimulus). The same type of conditioned learning was conducted in green pea plants, Pisum sativum L. [16]. Blue light was the “food” source, a fan was the neutral cue, and the response was growth toward the stimuli. Results from Gagliano et al. [16] demonstrated that the pea plants were able to associate the wind with where the light was going to be. In the absence of blue light, the plant was still able to associate that the direction of the blowing fan would determine where the light source would be. Not only did the green pea plants have to respond to two external stimuli, but it also had to internally and globally process that those two stimuli were associated. This type of learned behavior can be seen as an expression of an anticipatory behavior that required storing and processing information and globally responding [16]

(3) Salt avoidance in Arabidopsis thaliana (L.) Heynh

 Roots need to make the best overall decision. Apart from growing toward gravity, water, and nutrients, they must sense sources of stress such as salinity. Roots of Arabidopsis thaliana (L.) Heynh. Navigate belowground to avoid high saline conditions. The root apparatus possesses a sophisticated sensory and communication system that allows the plant to respond flexibly. Roots must integrate these and many other cues so as to grow one way or another under constantly changing conditions [23]

(4) Host preference in parasitic plants

 The parasite dodder (Cuscuta pentagona Engelm.) obtains its nutrients from the shoots of the host plant it climbs onto. By sensing the airborne volatile compounds that potential hosts emit, they are able to choose the more nutritious ones. In the vicinity of a tomato and a wheat plant, the dodder can tell them apart and grow toward the more nutritious tomato exemplar [25]

(5) Mycoheterotrophic parasitic plant (mere behavior)

 Mycoheterotrophic plants cannot do photosynthesis. They obtain all their water and nutrients from the fungi they parasite providing nothing in return. Many of them mimic fungi varieties other than their host, remaining belowground and becoming visible only when they flower. Their metabolic cost in doing so is minimal [54]

(6) Secondary metabolite manipulations of nectar in plant–ant relationships

 Many plants secrete extrafloral nectaries as food for ants in return for their protection. Plants need to attract the right kind of ant partner and actively maintain their quality protection. The nectar is custom-modified to specific ants. Too little nectar can discourage ants away while providing too much nectar can lower the quality of protection. These plants have to sense the presence of different ants, monitor and modify their activity accordingly in order to get the best benefits [19]

(7) Resource exploitation by roots

 In one study, roots belonging to the same pea plant (Pisum sativum L.) were exposed to two patches of nutrient: one patch with more amount of nutrients but whose concentration remained constant, and a second patch with less amount of nutrients, but whose concentration would increase throughout the experiment. The pea plants grew more roots to the patch that currently had less amount of nutrients, but would have more in the future due to the steady increase [26]

(8) Plant defense turning herbivores into cannibals (mere behavior)

 Some tomato plants (Solanum lycopersicum L.) are able to defend themselves against herbivory by releasing certain chemicals (methyl jasmonate). Researchers observed that spraying the tomato leaves with methyl jasmonate promoted cannibalism: munching caterpillars would prefer to change diet and eat other fellow caterpillars instead [55]

(9) Numerical sensitivity and short-term memory: Venus fly trap, Dionaea muscipula J.Ellis

 The Venus flytrap, Dionaea muscipula J.Ellis, snaps shut when it gets mechanically stimulated twice. After the first stimulation, the second needs to occur within 20 s of the first to snap shut. If it does not, then it resets. While counting to two may seem less impressive, counting to five is more difficult to do. Before digestive enzymes are secreted, the Venus fly trap needs to keep counting the numbers of mechanical stimulation until it reaches five. It is the plant’s extra security mechanism. Dionaea spp. are able to count, store information as a form of short-term memory, and repeat the process [14]