A seasonal phenological study of the temperate fern Cystopteris fragilis

Cystopteris fragilis L., a desiccation-tolerant fern species growing on a stone wall (Palisades, NY), was studied from April to September 2024 to document leaf phenological development during a season favorable for growth. The first leaves (ca. 5–7 cm in length) emerged in April. Mature, sori-bearing leaves (15–30 cm in length) appeared in June and persisted until late September, when the majority either dehisced or became dry and decumbent. In June, leaves had a mean specific leaf area of 269.97 ± 12.93, a mean chlorophyll concentration index of 3.56 ± 0.35, and a mean maximum photosynthesis rate of 3.90 ± 0.28 µmol m−2 s−1. Mean stomatal length was 41 ± 0.60 µm, and mean width was 26 ± 0.37 µm. Mean stomatal density in mature leaves was 4,000 ± 200. By September, the mean maximum photosynthesis rate had decreased to 2.30 ± 0.20 µmol m−2 s−1. With respect to leaf fluorescence data, there was a small but statistically nonsignificant decline in mean Fv/Fm during September. Among the more significant findings is the relatively major change in the physiological parameters of this species during autumn, particularly the decline in electron transport variables (ETo/RC and ψ0) in autumn compared with summer (p < 0.05), coupled with a somewhat lower efficiency of photosystem II (Fv/Fm). These changes may contribute to the decline in the photosynthesis rate observed during the transition into dormancy of this desiccation-tolerant species.