アジサイ科アジサイ属の落葉小低木で、学名は Hydrangea serrata var. megacarpa。英名はありません。
The "Ezo-ajisai" (Hydrangea serrata var. megacarpa) belongs to Hydrangeaceae (the Hydrangea family). It is a samll deciduous tree that is distributed from Hokkaido to the Japan Sea side of Honshu and Kyushu. This tree grows in semi-shade places along mountain streams and can reach 1-1.5 m in height. The corymbs are borne on the new branches and bloom pale bluish-purple bisexual flowers at center, neuter flowers at around the periphery from June to August. The mother species, "Yama-ajisai", is distributed in the Kanto region and westward in Honshu, and has smaller inflorescences and leaves.