Résumé
Cladoxylopsids originated during the Early Devonian and became extinct in the early Carboniferous (Durieux et al., 2021). The youngest known cladoxylopsids date from the Tournaisian (ca. 360-345Ma) and belong to the genus Cladoxylon, predominantly found in European localities. While most cladoxylopsids have been reconstructed as self-supporting plants (e.g., Soria and Meyer-Berthaud, 2004; Giesen and Berry, 2013), a preliminary biomechanical analysis suggested that it may not have been the case for C/adoxylon (Soria et al., 2006). In this study, we use 50 anatomically preserved specimens of C/adoxylon from the Lydienne Formation, Southern France, to investigate the affinities, development, and architecture of this genus in more detail.The specimens are up to 9.5 cm long and 6.5—-30 mm in diameter. They all share (1) dissected steles, (2) mesarch protoxylem strands located at tips of peripherical xylem ribs, and (3) a cortex made of two zones, one parenchymatous and one sclerenchymatous peripherically. Differences between specimens include (1) the shape and number of peripherical ribs, (2) the presence/ absence of central vascular bundles (1e., circular structures devoid of protoxylem strand), (3) the lateral organ emission process, and (4) the amount of secondary xylem.We identified 3 taxa (Cladoxylon mirabile, C. taeniatum, and C. taentiatum form dubium), already known in coeval deposits of Saalfeld (Germany), as well as potential new species. Investigation of lateral organ emission indicates that they possess an abaxialadaxial polarity and bore non-planated ultimate appendages.A multivariate analysis of a sub-sample of well-preserved specimens has also been conducted. Using the analysis results and qualitative findings, we discuss the possibility that these Cladoxylon morphotaxa represent various developmental stages of the same plant, different species, or both. These findings about the development and architecture of Cladoxylon lead to new hypotheses about the genus growth habit.