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.
Leaves alternate, exstipulate, imparipinnate. Flowers regular, polygamous, large, white, in terminal simple racemes; pedicels long, bracteate at the base. Sepals 5, boat-shaped, imbricate. Petals 5, elongated, clawed, without scales. Stamens 8. Capsule as large as an apple, corticate, 3-celled, with several seeds in each cell, splitting loculicidally. Name from yellow, and KEpas, a horn.
1. X. sorbifolia. - The only species, still very rare in gardens, It is a beautiful hardy tree of small stature, with leaves resembling those of Pyrus Aucupdria, and white flowers with a purple eye. The spot at the base of each petal is primarily yellow, hence probably the generic name. A native of North China.