AbstractOur finding of extensive off-shore meadows ofPenicillus capitatusin the Canary Islands is the first direct observation of this species off the eastern Atlantic islands. Populations form scattered patches between 20 and 27 m depths, leading to denser meadows between 28 and 50 m depths. Total population coverage is ca 11.16 ha. Plant morphology, cover and density changed through the year. In September, well-developed individuals were dominant whereas theEspera-phase was dominant in January and March. The highest mean cover and density values were 75.42% cover and 1245 well-developed individuals m-2, respectively. Specimens reach only 6 cm in height, which is shorter than individuals from the Mediterranean Sea and the Western Atlantic, and they often grow intermixed with species ofCaulerpaandHalophila decipiens. It is difficult to determine whether this is a recent introduction, because the species may have been overlooked in the past. Nevertheless, the extensive meadows found in La Palma may be related to recent increases in sea water temperature, and the tropicalization of the marine flora and fauna of the Canary Islands detected during the past decade.