Seed dormancy and germination in the giant Himalayan lily (Cardiocrinum giganteum var. giganteum): an assessment of its potential for naturalization in northern Japan

Understanding the potential for ornamental plant species to become naturalized in a nonnative habitat requires information on seed germination in order to help predict responses of the species to the natural environmental conditions of its new habitat. Cardiocrinum giganteum var. giganteum, which is native to the Himalayas, has been introduced as an ornamental plant in temperate regions of the world, and was categorized recently as invasive in New Zealand. Seed germination requirements of the species were determined under natural conditions in Hokkaido, Japan, to assess its potential to become naturalized in this region of Japan. Mature seeds were collected from its native range in the Indian Himalayas. At maturity in autumn, seeds had underdeveloped embryos, which grew in the second autumn and winter after exposure to summer temperatures. Radicles and cotyledons emerged in late winter and spring. Thus, an 18?C19?month period was required from dispersal to seed germination. Under laboratory conditions, this period could be shortened to 10?C11?months in a 25/15?°C (120?days)????15/5?°C (90?days)????0?°C (90?days)????15/5?°C (60?days) temperature sequence. GA₃ did not substitute for the above temperature requirements. These temperature requirements for seed germination of C. giganteum var. giganteum are very similar to those of its native Japanese congener C. cordatum var. glehnii. Seeds of both taxa have deep simple morphophysiological dormancy. The close similarity in the requirements for regeneration from seeds of the two taxa suggests that the seed stage of the life cycle is not an impediment to the naturalization of the giant Himalayan lily in northern Japan.