Résumé
Aerenchyma is a plant tissue that enables internal gas transport. It forms either as part of the normal development or in response to environmental stimuli, and is considered an adaptationto hypoxic conditions (submersion of all or part of the plant). It can develop either schizogenously, through cell separation and expansion of intercellular spaces, or lysogenously, via apoptosis, leading to the formation of air-filled lacunae within the cortex of stems, roots, and/or leaves in extant plants 1. Fossil evidence for the emergence of aerenchyma remains scarce. The earliest known occurrences date from the Early Devonian, in the cortex of the lycopsid Asteroxylon from the Rhynie Cherts 2, and from the Late Devonian in the stem of the iridopterid Keratophyton from Australia 3, in the stem of the cladoxylopsid Pietzschia levis from Morocco 4, as well as in the petiole of Periastron reticulatum and Aerocortex kentuckiensis, which are known from the Late Devonian to the early Carboniferous in Kentucky, Germany, and France 5. In this context, the present study focuses on the presence of aerenchyma in several early Carboniferous specimens from the Lydiennes Formation (Montagne Noire, France). This particularly well developed aerenchyma has been observed in the cortex of a stem or branch attributed to a new cladoxylopsid relatedto Pietzschia levis, and in the petiole of Periastron reticulatum. The presence of aerenchyma in a foliar organ suggests an adaptation to an aquatic environment 6, implying that the plantwas at least partially submerged. These findings provide new insights into the evolution of aerenchyma and of the aquatic habit in vascular plants, and enhance our understanding of early Carboniferous floras in France.