Ever since Darwin: why plants are important for evo-devo research

Abstract

In this essay, I provide examples of: (i) the presence of fractal properties and a continuum of forms in living organisms; (ii) the potential contributions of plant evo-devo towards a general theory of development encompassing various multicellular organisms; (iii) the “arrival” of a wealth of forms in plants that cannot be explained by natural selection alone. As elucidated by evo-devo studies, evolutionary diversification is also due to, e.g., (epi)genetics, correlation, phenotypic integration, self-organization, and physical constraints. Four kinds of phyllotaxis patterns in vascular plants – from Fibonacci systems with divergence angles around 137.5° to spiral systems with divergence angles below 80° – are described and illustrated: Cycas (gymnosperm), Huperzia (clubmoss), Pandanus (screw palm), and Costus (corkscrew ginger). They serve as examples of morphogenetic variation in plants that call for evo-devo explanations beyond (or prior to) the “survival of the fittest”. Charles Darwin was already convinced that natural selection had not been the only driving force in evolution.