Evolutionary shifts in plant adaptation mediated by phytohormones

The transition of plants from aquatic to terrestrial environments imposed unprecedented ecological and physiological challenges, necessitating the evolution of sophisticated perception and response mechanisms. Phytohormones played a central role in this adaptive transition by orchestrating coordinated physiological and morphological adjustments that improved survival under variable terrestrial conditions. In this review, we examine the evolutionary origin, diversification, and functional specialization of the 10 classical phytohormones-auxin, cytokinins, gibberellins, abscisic acid, ethylene, jasmonates, salicylic acid, strigolactones, brassinosteroids, and peptide hormones-from the algal ancestors of land plants to angiosperms. The timing of the emergence of each hormonal signaling system is considered in parallel with the evolving ecological and physiological demands of terrestrial habitats, highlighting their roles in environmental sensing, stress responses across lineages, and the successful colonization of terrestrial environments and adaptation to life on land. Furthermore, we discuss how the sequential establishment and integration of these networks increased physiological complexity, coordinated growth and development, and provided competitive advantages under fluctuating conditions, underscoring the central role of integrated hormonal signaling in the evolutionary success of land plants.