Résumé
The Devonian-Carboniferous period witnessed some very significant events in plant evolution. During this period, plants evolved numerous structures that impacted ecosystems worldwide, such as the first leaves, seeds, deep-rooting systems, and wood. In today’s flora, wood (secondary xylem) is only present in seed plants (angiosperms and gymnosperms); however, during the Devonian, ferns s.l., lycophytes, and some extinct seed-plant relatives were also woody. This period thus represents a unique window to study the origin and early evolution of wood.In this work, a new species from the Devonian of Ireland, Callixylon seamrogia, as well as two other woody species from the early Carboniferous of France, Stauroxylon beckii and Cladoxylon taeniatum, have been (re)described. These studies are participating in the effort toward a better understanding of the diversity of woody plant growth and taxonomical diversity duringthe Devonian -Carboniferous period.The Late Devonian is marked by multiple extinction events according to the fossil record of marine organisms, and questions on their impact on plants have naturally been raised. This work leads to new plant descriptions participating in the debate, and the phylogenetic study undertaken to recover the affinities of Stauroxylon beckii provides evidence of an additional group crossing the Devonian-Carboniferous boundary, the Aneurophytales.The last part of this work focuses on the description of a single slide of Sphenophyllum from the early Permian of France, representing the first evidence of a sphenophyte stem colonized by fungi. This finding provides a textbook example of how biased is our view of this fossil record, based on the origin of the slide, i.e., belonging to the co-worker of one of the fathers ofpaleomycology and of the study of Sphenophyllum. In addition, it is a first report of fungal remains preserved as trace fossils. This work aligns with the hypothesis explaining the “lack” of evidence of wood-degrading fungi before the late Carboniferous by a human bias in studying the fossil record of fungi.