Alien, introduced, and non-native species expand their distribution through the development of various transportation networks. In Japan, Ligustrum lucidum Aiton (Oleaceae) was introduced in the mid-1800s for use as roadside trees, but has escaped from the planting area and spread everywhere. This species also invades coastal areas and has adapted to develop its characteristic features under various stress conditions. To clarify the adaptive features of L. lucidum in coastal areas, we conducted morphological and anatomical analyses. We found that the stomatal size of L. lucidum was smaller in the coastal populations than in inland populations, which is similar to the coastal adaptation pattern of L. japonicum Thunb., a closely related native species. Our results suggest that strong selective pressure on coastal area conditions could force their leaves to avoid excessive transpiration, and such an adaptation pattern of L. lucidum could expand its distribution to various coastal areas.

Lysimachia mauritiana Lam. (Primulaceae), a biennial maritime plant, is widely distributed in East Asia, the Philippines, Micronesia, Polynesia, and the Indian Ocean. Because of this species’ wide distribution in Japan, we hypothesized that it could germinate and grow even in the bare coastal areas damaged by the tsunami caused by the Great East Japan Earthquake. Thus, we aimed to evaluate the seed germination of L. mauritiana under different sowing depths, temperatures, and salinity soil conditions. The highest germination rate was obtained by sowing L. mauritiana seeds near the soil surface, with germination rate decreasing as the seeding depth increased. Lysimachia mauritiana germinated even at relatively low temperatures. Moreover, we found that L. mauritiana seeds could germinate in less than 1% salt water and in salt-accumulated soil, using soil soaked in 5% or 10% salt water. Our results therefore suggest that L. mauritiana seeds could germinate by sowing on the bare soil surfaces damaged by the tsunami.