This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Deciduous shrubs with opposite undivided entire exstipulate leaves and solitary axillary often fragrant or aromatic flowers. Sepals and petals in many series, the outermost small and bract-like, the inner petaloid, inserted on the outside of a fleshy urceolate torus having the appearance of the tube of a perianth. Stamens numerous, inserted at the mouth of the torus. Carpels many, free, included within the. tubular torus, 1- or 2-seeded; seeds erect, exalbuminous. A small group of about four species from North America and Japan. The only two genera referred here are both represented in our gardens.