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.
Trees or shrubs, often spinose or glandular-pubescent, with alternate simple stipulate leaves often 3- or 5-nerved longitudinally. Flowers often small and green, rarely blue, yellow, or white as in Ceanothus. Calyx small, tube coriaceous, with 4 or 5 valvate lobes. Petals concave, often on long slender claws. Stamens equalling and opposite the petals. Fruit various. There are 37 genera and about 430 species of this order, from the warmer and tropical regions of the whole world.
Paliurus aculeatus - a branching spiny shrub with small 3-nerved leaves, minute flowers, and curious dry fruits in which the disk is enlarged, forming a circular wing - is sometimes cultivated as a curiosity under the name of Christ's Thorn; and two or three species of the curious South American genus Colletia are occasionally met with in collections. They are leafless spiny shrubs, some of them with remarkably thickened and flattened branches, and small white or yellowish flowers.