Stomatal Study of Introduced Species, Ligustrum lucidum Aiton (Oleaceae), in Coastal Areas of Japan

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.