Reproductive success in a reestablished versus a natural population of Bidens Cernua L.

Seed germination capability and phenological trend of a natural population of Bidens cernua L. (included in the Red List of Italian Flora, as critically endagered species for the Latium) (NP) versus a reestablished (RP) one were analysed. The study was carried out at Posta Fibreno Lake (41°42’N, 13°41’E; 290 m a.s.l.). RP had the significant (p < 0.05) highest germination percentage (98%) and speed of germination (TD50 = 8 days) than NP (93% and TD50 = 9 days). Not significant differences in the length of the phenological phases were found between NP and RP. Seedling emergence happened in early May when the mean minimum air temperature was 10.0 °C and ended at the end of August, when the mean maximum air temperature was 29.8 ± 2.6 °C. Flower head production was significantly (p < 0.05) the highest in RP than in NP (4.2 ± 0.3 and 3.6± 0.2 flower head per plant, respectively). Not significant differences were found between the two populations in seed production per flower. The reestablished seedlings resulted in a new, self-sustaining population, and the new plants by the higher flower head, seed production and germination rate could have an advantage in the early stage of seedling establishment.