This book explores the emerging intersection of design, plant intelligence, and multispecies coexistence, with a particular focus on the relationship between plants and humans in urban public spaces. Rooted in recent findings from plant neurobiology and expanded through design theory, it challenges the entrenched perception of plants as passive, decorative resources and instead positions them as active, purposeful agents capable of interaction and influence within designed systems. By engaging with more-than-human and multispecies design, it underscores the importance of recognising and cultivating interspecies relations as a foundation for shaping plural, multispecies urban environments. At the core of this work lies the "Relational Atlas", a framework that decentres the human and reframes design space as relational space, where the shared interests of human and non-human agents converge at specific spatial and temporal nodes. Grounded in Critical Plant Studies, this framework informs participatory design practices that unsettle anthropocentric paradigms, highlight the ambiguous role of plants within urban ecosystems, and open pathways toward new forms of urban ecology.