Alien species often rapidly adapt and flourish in new habitats. The rapid evolution of invading species is one of the critical issues in biological invasion. It has been accepted that introduced plants grow larger and have more fecundities than compared to their native range. However, to our knowledge, no studies have focused on evolution of floral traits of introduced plants.

The tall goldenrod (S. Altissima L.) is a perennial herb that was introduced to Japan from North America approximately 100 years ago. In this study, we compared floral trait of S. Altissima the between in USA and Japan. We assessed inflorescence size, and female and bisexual flower rate of individual plants of five populations in the North America and five populations in Japan.

The inflorescence size of Japanese plant was significantly greater than in North American plants. The proportion of bisexual florets per capitulum was significantly lower in Japan. This is the first study showing sex expression of flowers was differ in native and introduced plants.