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.
Annual or herbaceous or shrubby diffuse perennials. Leaves entire or pinnatifid, often fleshy. Flowers racemose or corymbose, white or purple. Sepals equal at the base. Petals unequal; the two exterior larger than the others. Stamens free. Pod broad, compressed, ovate or orbicular, entire or bind at the apex; seeds one in each cell, not margined. About twenty species are known, nearly all inhabiting the Mediterranean region. Named from Iberia, Spain, where many species grow. They are all known under the English name of Candytuft.
1. I. amara (fig. 38). - An annual plant from 6 to 9 inches high, with white or purplish flowers about half an inch across, appearing in July. Western Europe, naturalised in England. As the specific name denotes, very bitter.
2. I. umbellata. - Also annual, and rather larger than the preceding, with flowers arranged more in the form of an umbel or corymb. It is genus it is sometimes referred. Leaves ovate-lanceolate, sessile, very hairy. Flowers bright yellow with a brown blotch at the base of each petal. A Summer-flowering plant from Portugal.
Fig. 38. Iberis amara. (1/4 nat. size.)
2. H. vulgare, Rock Rose. - This is the common native species, frequently seen in gardens, and one of the most widely distributed, being found from Arctic Europe to both shores of the Mediterranean. A dwarf shrub with opposite linear-oblong hairy leaves and usually yellow flowers, but varying in different shades to deep red. There is also a double-flowered variety. H. croceum, roseum, surrejanum, grandiflorum, etc., are simply varieties of this species.
There are numerous other species, few of which are seen in cultivation; but we might mention H. pulverulentum and H. macranthum, with white flowers; H. formosum and H. Tuberaria, an herbaceous species with ribbed leaves and yellow flowers with a purple blotch at the base of each petal.
3. I. odorata. - A pretty odoriferous annual species, a foot or more high, with large corymbs of pretty white flowers towards the end of Spring. A native of Crete.
4. I. sempervirens (fig. 39). - A shrubby branching evergreen species, about 9 inches or a foot high, with pure white flowers. This is the ordinary perennial species in cultivation, flowering in May. A native of Candia (hence the trivial name Candytuft), and other parts of Southern Europe.
5. I. Garrexiana. - A common plant in cultivation, very near No. 4, and by some considered a variety of it. The flowers, however, are smaller, and the racemes elongate very much in the course of flowering. It is a very hardy kind, a native of the South of Europe, flowering in Spring.
6. I. semperfidrens. - Shrubby, and similar to the last, but double its size, and flowering in Autumn and Winter. From the Levant.
7. I. Gibraltarica. - This is a magnificent species, bearing the largest flowers in the genus. It grows about a foot or more high, with oblong-spathulate leaves and pinkish-lilac or nearly white flowers. Native of the South of Spain, and still scarce in this country.
8. I. Pruiti. - The flowers of this nearly equal those of the last-named species, but here they are pure white. A somewhat shrubby plant, rarely exceeding a foot in height, producing an abundance of dark green foliage and compact heads of flowers, which appear in May or June. It is from the South of Europe.
9. I. Tenoreana. - Near Nos. 6 and 7, but hairy all over, and the flowers, white at first, change to a purplish red. South of Europe.
Fig. 39. Iberis sempervirens. (1/4 nat. size.)