Effect of selected environmental factors on the seed germination of the invasive species Polygala myrtifolia (Polygalaceae) in Australia

Context: Polygala myrtifolia L. has become a significant environmental weed in Australia, where it has invaded coastal ecosystems in temperate regions and there is a high risk of extensive further spread. Knowledge of seed-germination behaviour is essential to understand the potential future impact of this species. Aims: We investigated the effects of selected environmental factors and dormancy on P. myrtifolia seed germination and emergence to improve management strategies. Methods: Seeds were exposed to light, temperature, pH, salinity, osmotic potential and burial depth treatments to assess germination responses, dormancy and viability. Key results: Non-dormant seeds readily germinated to high percentages (93.0-95.0%) under specific day-night temperatures of 25°C-15°C regardless of light conditions and across all soil pH (75.0-100.0%). Salinities were tolerated up to 100 mM NaCl (70.0% germination) before sharply declining. Germination reduced from 98.3% to 40.0% at osmotic potentials of -0.4 MPa and -0.6 MPa respectively. Emergence was greatest on the soil surface (48.33%) and absent from depths of 8 cm. Conclusions: Germination was high during autumn, winter and spring conditions and across soils of any pH. The species is unlikely to invade areas of high salinity; however, it is moderately tolerant of low soil moisture during germination. Implications: There is high risk of P. myrtifolia further invading sensitive ecosystems because of its high germination success. Preventing seed dispersal and ensuring seedlings are controlled on emergence are critical to reducing its impact. We recommend that the cultivation and sale of this species should be prohibited across Australia to prevent further spread.