The foundations of plant intelligence

Abstract

Intelligence is defined for wild plants and its role in fitness identified. Intelligent behaviour exhibited by single cells and systems similarity between the interactome and connectome indicates neural systems are not necessary for intelligent capabilities. Plants sense and respond to many environmental signals that are assessed to competitively optimize acquisition of patchily distributed resources. Situations of choice engender motivational states in goal-directed plant behaviour; consequent intelligent decisions enable efficient gain of energy over expenditure. Comparison of swarm intelligence and plant behaviour indicates the origins of plant intelligence lie in complex communication and is exemplified by cambial control of branch function. Error correction in behaviours indicates both awareness and intention as does the ability to count to five. Volatile organic compounds are used as signals in numerous plant interactions. Being complex in composition and often species and individual specific, they may represent the plant language and account for self and alien recognition between individual plants. Game theory has been used to understand competitive and cooperative interactions between plants and microbes. Some unexpected cooperative behaviour between individuals and potential aliens has emerged. Behaviour profiting from experience, another simple definition of intelligence, requires both learning and memory and is indicated in the priming of herbivory, disease and abiotic stresses.

Keywords: assessment; behaviour; fitness; intelligence; plant; signals.

Figure 1.

Circumnutation uses a form of triangulation to locate the optimal direction of light. Large open arrow indicates growth direction. Smaller filled arrows indicate light direction and intensity. (a) The diagram illustrates the potential circular movement of a circumnutating seedling (dotted line). By movement in the form of a circle the shoot is able to compare continuously the light intensities at each stage of the rotation. The circumnutating shoot is using a form of spatial triangulation much as a snake uses its moving tongue to compare the density of prey chemicals on all sides and alter movement accordingly. In figure 1a, the assessed light intensity on all parts of the circle and on both sides would be about equal thus indicating a forward direction of growth. (b) In this case light (or in the case of dodder volatile chemicals) is to one side and thus the light intensity diminishes and then increases as the circle is moved through. This would signal a change in direction as indicated until again equal intensities throughout the circle are experienced. The requirements are memory of the variations in light intensity as the tissue moves around the circumnutatory circle and causing changes in movement to equalize out the light intensity. (Online version in colour.)

Figure 2.

Circumnutating Passiflora tendril changing direction as an offered support made of green plant materials is moved successively from position 1 to eventually 3 before removal altogether. At first no support was presented (situation a). Then the support was placed at position 1 (situation b). Clearly although continuing circumnutation, the tendril approached the support using triangulation as explained in figure 1 legend. When the tendril was near the support, it was moved to position 2 (situation c). As the tendril approached the support again, the support was moved to position 3 (situation d). Finally, in situation e, the support was removed altogether. Small arrows indicate direction of movement of tendril. The position of the support was identified and the tendril changed behaviour to pursue it rather as an animal predator pursues prey. The behaviour is similar to that of a dodder seedling identifying a potential prey from volatile chemicals and moving the vector of circumnutation towards it [93]. (Online version in colour.)