Land plant bodies exhibit both apical-basal and radial symmetry, and they are able to detect and respond to gravitational forces. These attributes were likely important factors in the success of earliest plants on land. This study focuses on features of charophycean green algae likely to have been preadaptive to early establishment of plant symmetry and gravitational responses, though most modern charophyceans occupy aquatic habitats where the buoyancy of water counteracts the effects of gravity. Trait mapping suggests that even the earliest-divergent modern members of the streptophyte clade have bodies whose symmetry departs significantly from the spherical condition, and that cellular mechanisms defining aspects of radial symmetry and polarized tip growth originated early. Genes, cell biological approaches, and taxa are identified for which further exploration is likely to illuminate early evolution of plant body symmetry and gravity responses.

Key words: apical-basal symmetry, charophyceans, gravity, radial symmetry, streptophytes, trait-mapping