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Origin of the vascular plant life cycle. The sporophyte in the last common ancestor (LCA) of land plants is an obligate matrotroph. The free-living sporophyte of the LCA of the vascular plants evolved by an expansion of gene expression such that the gametophyte body plan, already capable of free-living autotrophic existence, was substantially expressed in the sporophyte. S, sporangium; G, gametangiophore.
