**1. Introduction**

Global climate changes undoubtedly impact adaptability in plants by altering mechanisms of physiological plasticity [1]. Modifications in mechanism occurring at the morphological, anatomical, and physiological level are regulated by the capacity of a plant to adjust to abiotic and biotic stresses [1–4]. The resulting survival response and survival capacity may vary depending on plant life stages [1–4]. Plasticity mechanisms discovered in plants are like those described in animals and humans, illustrating the conserved connection between environmental selection and adaptive response [2, 3, 5–11]. Research into the connection between environmental stress, environmental selection, and plant plasticity has also identified both general and unique plasticity mechanisms that differ between wild, i.e., non-cultivated, and cultivated plant species [1, 12–15]. However, a review analyzing the contribution of key traits responsible for varied plasticity mechanisms in wild and cultivated plants has not occurred. Thus, the range of plasticity occurring in wild plants will be compared with plasticity mechanisms in cultivated plants. Similarities and differences in plasticity responses will be highlighted between the two groups, with a specific focus on climate imposed global abiotic stresses like drought [14].

All plants have evolved unique life cycle characteristics that enhance survival and adaptation to diverse short and long-term climatic events that limit resources. Phenotypic responses occur at every stage of plant development, and influence overall plasticity from one generation to the next. Understanding and tracking phenotypic plasticity of wild plants in cultivated plants first requires defining biological reaction norms and their alternatives to clearly illustrate the differences between biological plasticity and non-plastic responses. Examples of phenotypic responses include: (1) rapid seedling growth (2) a short vegetative phase, (3) deep root systems, (4) high seed output, (5) discontinuous or extensive seed dormancy, (6) efficient cellular defense machinery, and (7) environmental plasticity. Although all plants exhibit phenotypic responses, the level of response is largely influenced by the degree of cultivation. Several species of trees and weeds are exceptional models for defining and tracking the range of both short and long-term heritable characteristics of wild plasticity [1, 4, 12, 16–21]. Drought response studies in agronomically important, and highly cultivated crops like wheat, add perspective about the contributions of selective breeding programs; how increased cultivation results in gains or losses in adaptive responses and plasticity [7]. Transitional plant models, such as *Chenopodium quinoa* (quinoa) and *Hordeum vulgare* (barley) will be used to illustrate the evolutionary path from wild plasticity to cultivated plasticity.

## **2. Environmental changes impact phenotypic plasticity**

Climatic events trigger heterogeneous responses in plants. Plant responses occurring from biotic or abiotic factors drive two distinct adaptation mechanisms, natural selection and phenotypic plasticity. Both mechanisms reveal the full genetic capacity of plants [22, 23]. The genetic makeup or genotype of each plant species determines how a plant will react in new environments [24]. Accumulated exposure to novel environmental stresses over many generations may increase selection toward the frequency of favorable alleles versus a reduction of unfavorable alleles, and results in less genetic diversity [22]. Otherwise, in natural selection, any change in plant phenotype is defined as phenotypic plasticity [25]. Changes in phenotypic plasticity impact individual fitness without changing genetic diversity [22, 26]. Sometimes a novel genotypic response does not deviate from a normal range of reactions, i.e., the reaction norm, and sometimes it does [27]. Thus, plants have a wide array of genotypic responses that impact phenotype. Non-cultivated plant species like trees acquired wild plasticity through the combination of both the long-term accumulation of genetic changes and the conservation of favorable survival strategies through time [24]. Adaptive responses result in phenotypic plasticity [22, 26]. Adaptive responses also maximize phenotypic fitness, or the ability to respond and survive in changing environments [27]. Breeding programs have accelerated the adaptive process to abiotic stresses, like drought, in domesticated plant species by selecting for tolerance to drought or increased resource-use efficiency [28]. This approach has allowed breeders to select for favorable plant responses based on flexibility to varied environmental changes. A broad understanding of wild plasticity in non-domesticated plant species will enhance and extend our current understanding of the range of plasticity mechanisms in cultivated plants [2, 3, 5–11].
