Considerable progress has been made in documenting evidence of very early plants starting in the basal Ordovician employing dispersed spore, phytodebris, and mesofossil data. Macrofossil evidence is sparse until Late Silurian, but recent new data are improving our understanding of aspects of earliest plants. The considerable information about the possible source of cryptospores and trilete spores especially from the well-preserved mesofossils of the Late Silurian and Early Devonian is summarized. Promising avenues of research are the study of spore ultrastructure, and neo-paleo comparisons between newly discovered resistant components of extant bryophytes and fragmentary fossil remains. Recent macrofossil discoveries in the Late Silurian advance our understanding of early events in plant evolution and raise new questions about the timing of evolution or relationships among earliest (mostly vascular) plants.

The advent of wood (secondary xylem) is a major event of the Paleozoic Era, facilitating the evolution of large perennial plants. The first steps of wood evolution are unknown. We describe two small Early Devonian (407 to 397 million years ago) plants with secondary xylem including simple rays. Their wood currently represents the earliest evidence of secondary growth in plants. The small size of the plants and the presence of thick-walled cortical cells confirm that wood early evolution was driven by hydraulic constraints rather than by the necessity of mechanical support for increasing height. The plants described here are most probably precursors of lignophytes.

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known phylls, have the longest history of any group of vascular land plants. The early evolution of the group is reviewed concentrating on the Late Silurian and Devonian record of Lycopsida and Zosterophyllopsida. Distinct root-like and shoot-like axes in zosterophyllopsids and lycopsids are first recorded in the Early Devonian and can be compared to the later development of pseudobipolar growth of tree-shaped lycopsids with upward-growing trunks and branch systems and downwardgrowing rooting systems. The development of stigmarian rootlets postdates the evolution of pseudobipolar growth, first recorded in the Middle Devonian, according to current evidence. Other important events in early lycophyte evolution during the Devonian include changes in leaf morphology, modification of sporophylls, and the eventual appearance of the lycopsid strobili.

Available data on the stratigraphic ranges of latest Silurian and Devonian vascular plant macro-fossils (sporophytes) and spores provide insights into the tempo and mode of early tracheophyte evolution. Patterns of diversification, origination, and extinction conform in general to the predictions of Sepkoski's kinetic model of diversification. Rates of generic origination and extinction vary not only through time but also between organ systems for a single time interval. This fact, coupled with data on longevity and turnover and comparative morphological observations, can be used to document mosaic evolution in early vascular plant history. Mosaic evolution is an important theme in plant evolution; indeed, what we recognize as macroevolutionary events often correlate with brief periods of pronounced mosaicism. Such evolutionary patterns reflect the developmental biology of tracheophytes in which individual organs often have life spans that are considerably shorter than the life of the whole plant. Under these conditions, individual organs or organ systems can respond to different sets of evolutionary pressures.The major period of early vascular plant diversification occurred during the late Early and early Middle Devonian Period, 30 Myr or more after the origin of the group. Such lags in diversification are not uncommon in the fossil record. Sometimes they reflect extrinsic controls on diversification, but in other cases they appear to be a consequence of intrinsic rates of origination and extinction.