The royal fern (Osmunda regalis L.) is a threatened species, which reaches the northeastern border of its natural range in Poland. The number of royal fern stands is decreasing due to decline of its natural habitat – alder carrs. The main aim of this paper was to compare features of stands in habitats representing different levels of anthropogenic transformation and to investigate all stands of the royal fern in the ‘Baszków’ nature reserve (3.76 ha; Krotoszyn Forest District, Poland). We distinguished four plant communities within the nature reserve: Carici elongatae-Alnetum,
Molinio-Pinetum, Leucobryo-Pinetum and Pinus-Padus. In total, we found 144 royal fern specimens within the nature reserve area growing in 20 stands: 97 specimens in Carici-Alnetum (9 stands), 32 specimens in Molinio-Pinetum (4 stands) and 15 specimens along a drainage ditch (7 stands). Specimens from Carici-Alnetum had the highest proportion
of sporophylles (41%), which shows the habitat preferences of the royal fern. Low proportion of sporophylles and the low number of specimens in the stands in ditches prove lower vitality of royal ferns and possibility of local
extirpation in these stands. Royal fern populations in secondary habitats such as ditches and borders of forest divisions should be particularly monitored. Passive royal fern protection in the nature reserve gave positive results due to better availability of light, connected with mortality of some trees.