Anatomically preserved land plant fossils from the Lower Devonian Rhynie Chert contain conducting tissues that range from dark colored, elongated cells without secondary wall thickenings to tracheids similar to those of extant plants. Observed differences in conducting cell differentiation may or may not correspond to the physiological innovations of lignin biosynthesis and deposition. In order to evaluate the degree to which the morphological and physiological evolution were coupled in the tissues of early land plants, three analytical techniques were employed to study anatomically preserved fossils: electron microprobe analysis to obtain micron-scale resolution of elemental abundances, isotope ratio mass spectrometry to obtain millimeter-scale resolution of carbon isotopic abundances, and X-ray microscopy in conjunction with nuclear magnetic resonance spectroscopy to obtain micron-scale resolution of the preservation of organic molecular functionality. Studies demonstrate that original organics are not homogenized during diagenesis and are preserved in place with sufficient spatial resolution for paleobiological investigations. Tissue-specific isotopic and organic chemistry of Rhynie Chert plants suggests that the anatomical evolution of tracheid secondary thickenings and the biochemical evolution of lignin synthesis were originally independent: the earliest vascular thickenings were unlignified and cell wall lignification may have first appeared in other tissues. Only later were the anatomical and biochemical characteristics coupled to produce true tracheids like those of all living vascular plants.

Key words: geochemistry, lignin, paleobotany, Paleozoic, Rhynie Chert