Context The tree fern Dicksonia sellowiana (Dicksoniaceae) is endemic to the Neotropics, threatened with extinction in Brazil. Historical commercial exploitation, the slow growth of the species, and ongoing loss of forest habitat impose significant pressures, whereas its reproductive capacity remains poorly understood. Aims To (1) understand the relationship between spore production and maturation and environmental factors, and (2) evaluate in vitro germination and plantlet development from spores matured in different months to assess temporal reproductive variation. Methods Over a 12-month period, 25 individuals were monitored monthly to record fertile leaves with immature sporangia (FL-IS) and fertile leaves with mature, closed sporangia (FL-MS). Temperature, precipitation, photoperiod, and soil moisture were correlated with phenophases. In vitro spore germination and gametophytic development were assessed. Key results Temperature showed a positive relation with the percentage of plants bearing FL-IS and a negative relation with FL-MS. FL-MS were negatively associated with photoperiod and positively with precipitation. Highest spore germination rates were observed in winter and early spring, with successful gametophyte development in vitro and sporophyte formation on substrate under greenhouse conditions. Conclusions D. sellowiana has been observed to allocate the warmer months of the year to spore production, with spore maturation occurring during periods of lower temperatures, particularly in winter, within the Brazilian subtropical climate. Implications The reproductive pattern described here highlights the importance of low temperatures for spore maturation, which should be carefully considered when assessing population renewal under climate change scenarios and in efforts aimed at the conservation of the species.