HYDRANGEA, in botany; a genus of the dignia order, belonging to the decandria class of plants. There is but one species, viz. the arborescens, a native of North America, from whence it hath lately been brought to Europe, and is preserved in gardens, more for the sake of variety than beauty. It rises about three feet high; and hath many soft pithy stalks, garnished with two oblong heart-shaped leaves placed opposite. The flowers are produced at the top of the stalks in a corymbus. They are white, composed of five petals with ten stamens surrounding the style. It is easily propagated by parting the roots; the best time for which is the end of October. The plants thrive best in a moist soil, and require to be sheltered from severe frosts.