Seed traits and germination ecology of the rare steno-endemic Centaurea pangaea

This study presents the first assessment of seed biology in Centaurea pangaea, a narrow endemic species of Mt Pangeon (Greece). Seed production was quantified at both the capitulum and plant levels, and their morphometrics were measured. The seeds were categorized into naturally occurring color classes (white, beige, brown, and black), and their embryo viability was assessed. Germination was tested under cold stratification, gibberellic acid, kinetin, and control conditions. Nonparametric comparisons showed significant differences among classes, largely driven by the white class, as beige, brown, and black overlapped morphometrically. White seeds formed a distinct small-size class and were mostly non-functional, with only a minor fertilized fraction. Among colored seeds, fertilization rates were high (beige ≈58%, brown ≈78%, black ≈80%), but their viability was significantly lower (beige ≈35%, brown ≈50%, black ≈51%). Germination responses revealed a clear dormancy gradient indexed by color: beige seeds benefited from cold stratification, whereas both brown and black seeds behaved as essentially non-dormant, germinating well without pre-treatments. Therefore, color serves as a practical cue for dormancy status. The findings clarify seed biology in a narrowly distributed Mediterranean taxon and support future conservation actions.