The Role of Morphological Biochemical Reciprocity in Early Land Plant Evolution

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Abstract
A morphological-biochemical reciprocity is used to construct a scenario for the evolution of the land and vascular plant habits. The optimal designs of autotrophs are shown to be limited by their biosynthetic capacities, i.e., the morphological manner in which surface area-dependent functions are maintained with increasing size is primarily dictated by the availability of specific architectural polymers. The evolution of biosynthetic pathways (involving the detoxification-conversion of primary metabolites into useful architectural polymers, e.g., cellulose, lignin) predates and allows for transitions from simple dichotomous-convoluted morphologies to ‘tree-like’ erect plants. The reciprocity between morphology and biochemistry is seen to result in a stratified stability, i.e., optimal designs, parameterized by their biosynthetic capacities, result in a hierarchy of stable forms, which undergo transitions when environmental factors alter. Finite element analyses of geometric forms, showing a size increase with constant surface area-to-volume ratios, indicate simple lobed or convoluted structures are optimal designs for primitive non-vascular plants, while physical parameters defining the optimal design of erect plants indicate the necessity for differential tissue density. Selective pressures favouring an erect plant posture (photosynthetic rates; reproduction) coupled with a chemosynthetic ability to structurally reinforce specialized conductive cells is seen to result in the lignification of tracheid-like cells.