Reproductive Biology and Germination Ecology of Phytolacca acinosa in Its Secondary Range

Phytolacca acinosa Roxb., a perennial herb native to East Asia, is increasingly naturalizing in Europe, yet its reproductive ecology in the secondary range remains poorly understood. This study evaluated seed productivity across central and edge populations in the secondary range, fruit and seed morphometrics, and germination responses to cold storage, acid scarification (simulating bird endozoochory), and light exposure. Fruit production per raceme was influenced by an interaction between insolation and range position: reduced insolation increased fruit set in central populations but decreased it at the range edge. Raceme number per shoot was lower in spontaneous plants compared to cultivated ones. Fresh seeds exhibited strong dormancy with no germination without scarification. Acid scarification significantly enhanced germination, particularly with light exposure, reaching up to 55%. Cold storage did not increase germination percentage but accelerated germination of scarified seeds under light, reducing median germination time from 24 to 21 days. Compared to the congeneric P. americana, P. acinosa shows more stringent dormancy requirements. We conclude that P. acinosa retains deep seed dormancy in its secondary range and relies on bird-mediated endozoochory for both dispersal and dormancy release. At the northern range edge, reduced plant vigor and lower raceme numbers are partially offset by increased flower production per raceme, though fruit set remains constrained. The species does not exhibit the simplified germination requirements often associated with successful invaders; instead, its invasion success appears driven by a bet-hedging strategy combining persistent seed banks with specific dormancy-breaking cues.