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.
A small genus of Chinese and Japanese origin. Erect hairy herbs. Leaves alternate, ovate or cordate, and stem-clasping. Flowers in terminal panicles. Perianth six-parted, the segments forming a ball, clawed, the three outer bulging at the base. From three, and
swollen or hump-backed, referring to the outer perianth-lobes.