Seed germination ecology of the medicinal plant motherwort (Leonurus cardiaca)

Abstract

Leonurus cardiaca is a perennial mint species with a long history of use as a medicinal herb. It produces a wide variety of phytochemicals with pharmacological properties that are used to treat anxiety and sleep disorders, cardiac disorders, and to reduce inflammation. Surprisingly, scant information is available concerning its seed germination ecology. Hence, this study investigated the presence/kind of seed dormancy and the effects of several environmental factors on seed germination and seedling emergence. Seeds were collected from three populations, and they were subjected to germination and seedling emergence experiments in which environmental factors, including temperature, light, cold stratification, pH, osmotic stress, and depth of burial, were manipulated. Non-stratified seeds germinated over a range of alternating temperature regimes from 20/10 to 30/20°C, but they did not germinate at 15/5°C. Optimum germination occurred between 25/15 and 30/20°C. The presence or absence of light did not affect germination. Cold stratification at 4°C enhanced germination at the two coolest temperature regimes. Seed germination occurred over a solution pH range of 5–10 and exceeded 55% in buffer solutions with pH 6–10. Low levels of osmotic stress reduced germination; only 3–8% of seeds germinated at −0.2 MPa. Maximum seedling emergence occurred when seeds were placed on the soil surface, and emergence decreased with increased burial depths to 5 cm. Overall, seeds exhibited germination characteristics associated with type 2 non-deep physiological dormancy at maturity. Seeds primarily germinated at incubation temperatures of ≥ 25/15°C; however, conditionally dormant seeds became nondormant after prolonged exposure to cold stratification.