A prostrate evergreen shrub, growing from 6 to 12 in. only above the ground, but forming a wide-spreading mass. Shoots semi-herbaceous, slender, trailing, thickly covered with pale, bristly hairs. Leaves alternate, linear-oblong. 1⁄2 to 3⁄4 in. long, 1⁄6 in. wide, stalkless, blunt at the apex, dark dull green, clothed on both surfaces with pale hairs. Flowers stalkless, borne in the axils of leafy bracts on a terminal leafy elongated inflorescence, of a beautiful gentian blue, faintly striped with reddish violet. Corolla 1⁄2 in. long, tubular at the base, spreading into five rounded lobes at the mouth, hairy in the throat and externally; calyx with erect, hairy, awl-shaped lobes.
Native of W. France, the Pyrenees, and N.W. Spain, usually on acid soils and often found in association with Daboecia cantabrica; introduced in 1825. A singularly beautiful sub-shrubby plant, very effective in the rock garden, or at the top of banks over which its trailing shoots may hang. It also grows well if planted among heaths and allowed to clamber through them. It does not need a rich or wet soil, but one of a light nature, well drained, and neutral or slightly acid. Although not really tender, it detests winter wet, and is a complete failure in gardens where the soil lies soggy and cold in winter. It should be planted in full sun. Increased by cuttings in summer, and kept in pots the first winter. Where the soil and exposure are suitable it makes delightful patches in front of a low shrubbery or border, flowering continuously during May and June, often again later. It should be lightly trimmed after the main flowering is over.
In the 19th century L. diffusum was represented in gardens by plants with dark blue flowers, streaked with red. But early in the present century Messrs Perry of Enfield put into commerce ‘Heavenly Blue’, with larger flowers of a purer and paler blue, which quickly displaced the older forms and long remained without rival. Messrs Perry obtained their stock from E. A. Bowles, who had received his original plant from Dr D. H. Lowe (Journ. R.H.S., Vol. 52, p. 255). But whether it arose as a garden seedling or was collected in the wild is not known. In the 1930s ‘Grace Ward’ came into commerce, with larger flowers than in ‘Heavenly Blue’ and of less spreading habit.
L. fruticosum L. Lithodora fruticosa (L.) Griseb. – Allied to L. diffusum but of erect habit and with the corolla glabrous on the outside and in the throat. A native of the W. Mediterranean, found in hotter and drier places than L. diffusum and always on limestone soils.