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, shrubs, or herbs of very diverse habit. Leaves bisti-pulate, alternate, rarely opposite, pinnate, digitate, or more rarely simple; leaflets entire, lobed or toothed, sometimes stipellate. Inflorescence various. Flowers irregular, usually hermaphrodite. Sepals normally 5, more or less united, the fifth lobe anterior, the two posterior sometimes combined, forming a bilabiate calyx. Petals 5, unequal, imbricate, erect, rarely spreading; the upper one (standard) free, broad, often reflexed; the two lateral (wings) enclosing and sometimes adhering to the two lower (keel), rarely smaller; the two lowest inside the others and usually more or less united and curved upwards. Stamens 10, perigynous; filaments united in a sheath, or the upper one free or rarely all free. Fruit a 1-celled pod, dehiscent along one or both sutures, or rarely indehiscent, sometimes transversely septate; seeds 1 or more, inserted on the ventral suture, exalbuminous. As thus characterised this includes only one sub-order; but altogether the order includes some 400 genera and 6,500 species.