Learning in plants: A conceptual and experimental primer.

Whether plants are capable of associative learning remains a contested question, often complicated by conceptual ambiguity and methodological limitations. This article provides a critical and constructive primer on how to investigate associative learning in plants within a rigorous experimental framework. We begin by clarifying the concept of associative learning and distinguishing it from related phenomena such as habituation, sensitisation, and pseudo-conditioning. We then identify a set of minimal behavioural prerequisites that any system must satisfy to support associative processes. Evidence from plant biology indicates that plants possess these prerequisite capacities across multiple temporal and organisational scales. We further review historical and recent experimental attempts to demonstrate associative learning in plants, highlighting recurring methodological limitations. Building on principles from the experimental analysis of behaviour, we outline key design requirements for plant-conditioning studies, including identifying appropriate unconditioned stimulus-response (US-UR) complexes, operationalising conditioned stimuli, and implementing controls to rule out non-associative explanations. As we argue, adequately controlled experiments have not yet provided robust evidence for associative learning in plants, leaving open whether these capacities are integrated in ways that enable plants to form learned associations. By integrating behavioural theory with advances in plant physiology and imaging, future research can move beyond suggestive findings toward decisive tests. More broadly, this work contributes to a functionally grounded understanding of learning that does not presuppose a nervous system, thereby expanding the comparative scope of cognition across living systems.