This study reports the harvesting, management, trading and use of the royal fern (Osmunda regalis) in Cantabria (Spain), where medicinal plant gathering has been mainly abandoned and nowadays only few species are still commonly gathered. We interviewed 50 adults of different age, sex, and origins to obtain information on local knowledge and management practices of royal fern. Osmunda regalis is locally considered a highly efficient remedy. The rhizome has been traditionally employed in Cantabria mainly for the treatment of bone fractures, joint disorders and rheumatic and arthritic pain. Its consumption prevails in rural areas but it is also employed in towns and cities and its demand has led to small-scale marketing. More than half of the interviewees (54%) had only passive knowledge about their medicinal uses while the rest of informants (46%) were consumers, collectors or sellers (22% ‘collector-consumers’, 6% ‘non collector-consumers’, 4% ‘collector-sellers’ and 14% ‘non collector-sellers’). People from villages harvested O. regalis for their own consumption and expressed concern about overexploitation by a rising demand from urban areas, whereas people from cities were unaware of the ecology of the fern. The scarcity of the fern has led to rural residents to develop local management practices that contribute to the species conservation. These practices included keeping the location of the fern secret, not harvesting the complete rhizome for not killing the plant and allowing its regeneration, and cultivating the species in home-gardens. The inclusion of local knowledge in harvesting regulations might result in environmental norms accepted and internalized by the local population.