My talk aims to critically reconstruct the little-known legacies of Soviet plant philosophy and evolutionary theory, bringing them in dialogue with metabolic Marxism. The aim is to develop a new conceptual language to think about solidarity and cooperation across species boundaries, moving away from an evolutionary model built on lineage and competitive branching (the tree) to a systemic view driven by symbiosis (the web). It revisits the symbiogenetic theory of Boris Kozo-Polyansky and its later update by Lynn Margulis (who read Kozo-Polyansky alongside Vladimir Vernadsky), in order to articulate a model of solidarity for our current ecological crisis. Against evolutionary narratives centred on competition, cost-benefit, and the survival of the fittest, Kozo-Polyansky’s Symbiogenesis (1924) proposed cooperation as the motor of evolutionary innovation. Symbiogenesis reframes life as a web rather than a tree: evolution proceeds through horizontal fusions and metabolic entanglements across species boundaries. Organisms appear not as bounded individuals but as consortia, that is, political-social federations of semi-autonomous beings. Such a framework also challenges traditional notions of the biological individual, a topic already debated in 19th-century biology, most notably by Ernst Haeckel. I argue that the shift from tree to web – from individual to collective – in Soviet evolutionary paradigms offers more than just a biological hypothesis; it prefigures a politics of solidarity beyond exchange value. Symbiogenesis models a non-teleological and discontinuous transformation (“nature makes leaps”) in which new forms emerge from metabolic collaboration and exchange. Reading Kozo-Polyansky’s dialectical biology alongside Marder’s plant philosophy and Margulis’ model of planetary symbiosis which informed her Gaia theory, the paper proposes an ethics of symbiogenesis: solidarity as integration before differentiation, as collective becoming in the web of life.