Seed dormancy and germination of Epimedium koreanum Nakai

Epimedium species are shade-tolerant perennials with flowers and leaves that vary in color, making them valuable groundcover plants. We investigated the dormancy of E. koreanum seeds and their requirements for embryo growth and germination. First, the phenology of embryo growth, germination, and seedling emergence under field conditions were observed. Then, the effects of temperature sequences and gibberellic acid (GA3) treatment on dormancy and germination were evaluated in two laboratory experiments. Under field conditions, the underdeveloped embryos grew very little from June to early September, while rapid growth of the embryos was observed from late September to November. Embryo growth was completed by early December, resulting of 16-fold increase of the initial length of the embryo. The seeds had germinated in March of the following year, and the germination percentage reached 84.4 %. In the laboratory experiments, embryos hardly grew when the seeds were incubated at a constant temperature of 20 or 15 °C. When the seeds were warm stratified at 25 °C and then moved to lower temperatures of 20 and 15 °C, the embryo grew rapidly. Germination then occurred after cold stratification at 5 °C for 12 weeks. However, if seeds were subjected to cold stratification first, the embryo did not grow, and no seeds germinated. GA3 treatment increased embryo growth in the seeds, but few seeds germinated less than 10 %. Based on these results, seed dormancy of E. koreanum can be broken through warm followed by cold stratification. Therefore, the seeds can be classified as having deep simple morphophysiological dormancy. This is the first report of the ecophysiology of seed dormancy and germination in the genus Epimedium in the Korean peninsula.