Seed heteromorphism is a critical adaptive strategy for invasive plants to cope with environmental heterogeneity. To investigate the response mechanisms of heteromorphic seeds of Cenchrus spinifex， we examined germination characteristics of its two seed types （M-type： larger； P-type： smaller） under varying light （complete darkness vs. 12 h light/12 h dark） and moisture conditions （simulated by PEG gradients）. Subsequent seedling growth， biomass allocation， and phenotypic plasticity were analyzed in response to the interaction between water availability （normal， mild， and severe drought） and light intensity （high and low intensity）. The results showed that germination was unaffected by light but strongly inhibited by water stress； under severe drought， M-type seeds outperformed P-types in root length， bud length， and biomass. As seedlings， M-type plants showed higher phenotypic plasticity in morphological traits （plant height， tiller number， leaf area）， favoring increased aboveground resource investment for rapid life cycle completion， whereas P-type plants exhibited greater plasticity in biomass allocation， enhancing stress tolerance through increased root biomass proportion. In summary， the complementary germination and growth strategies of heteromorphic seeds in C. spinifex represent an effective “bet-hedging” mechanism， which is crucial for its successful invasion and spread across environmentally stressful and variable habitats.

Invasive plants  /  Cenchrus spinifex Cav.  /  Seed heteromorphism  /  Phenotypic plasticity  /  Biomass allocation