Marine conservation in the subtropical North-East Atlantic requires a precise understanding of the distribution of its endemic species, particularly within under-explored ecosystems. Avrainvillea canariensis, an endemic Macaronesian green macroalga, listed in the Canary Islands catalogue of protected species, has long been considered rare, occurring as solitary individuals associated with algal assemblages or seagrass beds. Here, we document a mesophotic habitat not previously reported from the Canary Islands, consisting of extensive and dense meadows formed exclusively by A. canariensis off the island of El Hierro. Our observations extend the species’ known distribution, establishing a new southernmost limit within the Macaronesian region. Algal meadows were detected using stereo Baited Remote Underwater Video Systems, occurred at 40–45 m depth, and reached a maximum density of up to 100 individuals/m2. These meadows may form complex habitats, as they seem to be actively utilized by a variety of marine fauna, including emblematic species and fish of economic importance. This study provides the first quantitative description of persistent populations of A. canariensis in the archipelago and highlights the need for systematic mapping of mesophotic zones to accurately determine the distribution and ecological roles of endemic habitat forming species.