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.
Dwarf prickly or unarmed shrubs with 1-foliolate leaves or none, very rarely 3-foliolate. Calyx campanulate, the upper lobes free or connate. The claws of the lower petals connected with the staminal tube. Keel usually bent downwards. Pod short or long, flat or swollen. About seventy species are described, inhabiting Europe, North Africa, and Western Asia. Some derive the name from the Celtic gen, a bush; and others from the Latin genu, a knee.
1. G. alba, syn. Spdrtium album, S. multiflorum, and Cytisus albus. Portugal Broom. - A handsome species growing about 4 to 6 feet high, with numerous slender slightly furrowed erect branches and few scattered leaves of 1 or 3 small hairy leaflets. Flowers very abundant, white or pink, produced from May onwards for a considerable period. A native of Spain and Portugal, and the most desirable of its class.
2. G. sagittalis. - This is a very peculiar and interesting plant, in which the leaves are replaced by a foliaceous or winged jointed stem. It grows about a foot high, and bears terminal erect few-flowered racemes of yellow flowers in May or June.
3. G. tinctdria. Grreenweed. - A native species and one of the handsomest. A spineless shrub from 1 to 2 feet high with unifoliolate nearly glabrous leaves and a profusion of yellow flowers from July till September. There is a good double-flowered variety of this.
4. G. radidta, syn. Spdrtium radiatum. - A slender shrub about 18 inches high with opposite branches, 3-foliolate leaves, narrow leaflets, and terminal heads of yellovw flowers. A native of Italy, flowering in Summer.