The hydrangea, Hydrangea, is a shrub of showy rounded flower-clusters, many species native to East Asia and the Americas; its name comes from the Greek for water-vessel, given for the cup-shaped seed capsule and reflecting the plant's great thirst for water. In Japan the hydrangea, ajisai, is the flower of the rainy season of early summer, its blue and violet heads famously associated with temple gardens in the rain, and it features in the Buddhist festival of the Buddha's birth, when a sweet tea, amacha, brewed from a related hydrangea is poured over the image of the infant Buddha.
A plain caution belongs beside its beauty: hydrangea leaves and flower buds contain cyanogenic compounds and are toxic if eaten in quantity, capable of causing vomiting and, rarely, more serious illness in people and pets, a genuine hazard worth stating plainly despite the plant's cheerful and devotional associations. Some Asian hydrangea species have long been distinguished by regional folk practice from the more ornamental garden varieties grown in the West, though the ordinary garden hydrangea sold in nurseries worldwide should not be treated as a food or tea plant on the strength of these separate and specific regional traditions.