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.
Deciduous or evergreen shrubs. Leaves membranous, often ciliate and hairy, mucronate. Flowers large and showy, often glandular and clammy, expanding before the new leaves are fully developed. Corolla funnel-shaped. Stamens exserted, usually 5, filaments long. Botanists now unite this with Rhododendron in consequence of the discovery of species intermediate in character; but it will be more convenient to keep the hardy species separate in this work, because they are so universally known under these distinctive names. The species referred here are not so numerous, but the genus has much the same range. The name is from parched, in allusion to the natural habitats of some species.
1. A. Pontica. - This species is a native of Asia Minor, and ordinarily grows from 3 to 6 feet high, with lanceolate soft hairy leaves and yellow or orange flowers sometimes tinged with red.
2. A. calendulacea.- A North American species of about the same stature. Leaves obovate-oblong, hairy. Calyx-lobes oblong. Tube of the corolla shorter than the lobes, hairy. Flowers large, numerous, orange-coloured.
3. A. nudiflora. - Near the last in characters, and from the same regions. Corolla-tube glandular, scarcely exceeding the broad lobes. The flowers vary from pink to deep purple. Both flower in Spring.
A, viscosa and A. arborescens, North American species, produce the flowers before the leaves, the former having a long tube to the corolla, and the latter being quite smooth in all its parts.
The foregoing forms, in conjunction with A. visosa and A. speciosa, and perhaps some other species or wild varieties whatever they may be, have given birth to the numerous varieties now in cultivation, partially from natural variation and partially by intercrossing. In colour they range from white through every shade of yellow, orange, and red to crimson, and many uncommon intermediate tints. There are also hybrid forms between some of these and the true Rhododendrons, especially between Rh. Ponticum and A. Sinensis, syn. A. mollis, a species very near A. Pontica, with larger yellow or orange flowers and elliptical leaves. The hybrid called Rh. praecox superbum has flowers in the shape of an Azalea, of a lilac colour, and very small dark green persistent leaves.
The species belonging to this division are not so hardy as the foregoing, and usually treated as greenhouse plants. They are usually of smaller more compact growth. The Indian
Azaleas have sprung from A. Indica (fig. 160), and some other species or natural varieties introduced from China. Some of these forms, as A. liliiflora (fig. 161), are said to be quite hardy.
Fig. 160. Azalea lnaica. (1/4 nat. size.)
Fig. 161. Azalea liliiflora. (1/3 nat. size.)