Hydrangea macrophylla var. thunbergii
A variety of bigleaf hydrangea whose leaves are used to make 甘茶 (amacha), a sweet herbal tea.
See also: 甘茶
The leaves of the amacha-no-ki are dried to make amacha (sweet tea).
The name literally means 'sweet tea tree', from 甘茶 (amacha, sweet tea) + の (possessive particle) + 木 (ki, tree).