Fig. 3.

Phylogenetic distribution of lignification patterns and ionic mediation of xylem hydraulic properties. Descriptions of terminal taxa are based on current analyses of living plants. Gray boxes indicate inferred lignification states for extinct ancestral vascular plant and seed plant groups based on previous x-ray spectromicroscopic and taphonomic studies of fossils (3, 4, 6, 8, 11), except for the state of ancestral seed plants hypothesized here based on comparison of anatomy and reconstructed whole-plant morphology with that of extant plants analyzed in this study. Hypotheses concerning ancestral states are testable with further geochemical analysis of fossils.