Abstract
A new taxon of lignophyte is described based on a permineralized stem from the Late Tournaisian (Lower Carboniferous) of the Central Ahnet region, Algeria. It shows similarities with arborescent seed plants described in the Lower Carboniferous of Europe and North America such as Eristophyton waltonii Lacey and Cauloxylon ambiguum Cribbs. However, the primary and secondary vascular system of the stem display an original combination of characters and it is assigned to a new genus: Ahnetia. The preservation of extraxylary tissues (secondary phloem, periderm, cortex) allows formulating hypotheses on the stem's growth potential. The early appearance of a periderm indicates that Ahnetia was capable of significant secondary growth and that the specimen likely represents a young axis of a larger plant. By its Late Tournaisian age, this specimen represents the oldest known occurrence in North Africa of a lignophyte capable of significant secondary growth after the extinction of the progymnosperm Archaeopteris.