The other species in the genus Hydrangea:

Hydrangea hirta / Koajisai
Hydrangea hirta f. albiflora / Shirobanakoajisai
Hydrangea luteo-venosa / Kogakuajisai
Hydrangea paniculata / Noriutsugi
Hydrangea paniculata. f. debris / Hidakanoriutsugi
Hydrangea petiolaris / Tsuruajisai
Hydrangea serrata / Yamaajisai
Hydrangea serrata var.megacarpa / Ezoajisai

Hydrangea petiolaris / Tsuruajisai ツルアジサイ