S. MEDIA (syns S. confusa and S. oblongifolia).—­Northern Asia, etc.  The pure white flowers of this species are very freely produced in corymbs along the shoots of the previous season during the months of June and July.  The lanceolate-elliptic leaves are serrate, or the smaller ones toothed near the apex only.  Within the past few years the species has been brought into prominence for forcing purposes, for which it is admirably suited.  It forms an upright, branching bush usually about 3 ft. high, and is best known under the name of S. confusa.

S. PRUNIFOLIA.—­China and Japan, 1845.  A twiggy-branched shrub growing 4 feet or 5 feet high, with oval, Plum-like leaves, and white flowers.  There is a double-flowering variety named S. prunifolia flore-pleno, which is both distinct and beautiful.

S. ROTUNDIFOLIA.—­Round-leaved Spiraea.  Cashmere, 1839.  A slender-branched shrub, having downy shoots, and round, blunt leaves, flowering in July.

S. SALICIFOLIA.—­Willow-leaved Spiraea.  Europe, and naturalised in Britain.  An erect-growing, densely-branched shrub, with smooth shoots, which spring usually directly from the ground.  Leaves large, lanceolate, smooth, doubly serrated, and produced plentifully.  Flowers red or rose-coloured, and arranged in short, thyrsoid panicles.  It flowers in July and August.  S. salicifolia carnea has flesh-coloured flowers; S. salicifolia paniculata has white flowers; and S. salicifolia grandiflora has pink flowers as large again as the type.  S. salicifolia alpestris (Mountain Spiraea) grows fully 2 feet high, with lanceolate, finely-toothed leaves, and loose, terminal panicles of pink or red flowers.  From Siberia, and flowering in autumn.  S. salicifolia latifolia (syn S. carpinifolia), the Hornbeam-leaved Spiraea, is a white-flowered variety, with leaves resembling those of the Hornbeam.  From North America.

S. SORBIFOLIA.—­Sorbus-leaved Spiraea.  Siberia, 1759.  A handsome, stout species, 4 feet high, with large, pinnate, bright green leaves, and small, white, sweetly-scented flowers produced in thyrsoid panicles.

S. THUNBERGII.—­Thunberg’s Spiraea.  Japan.  The white flowers of this species smell somewhat like those of the Hawthorn, and are freely produced on the leafless, twiggy stems, in March or early in April, according to the state of the weather.  They are borne in axillary clusters from buds developed in the previous autumn, and are very welcome in spring, long before the others come into bloom.  The bush varies from one to three feet high, and is clothed with linear-lanceolate, sharply serrated leaves.

S. TOMENTOSA.—­Tomentose Spiraea.  North America, 1736.  This species grows 2 feet or 3 feet high, has rusty tomentose shoots and leaves, and large, dense, compound spikes of showy red flowers.  Flowering in summer.

S. TRILOBATA (syn S. triloba).—­Three-lobed Spiraea.  Altaian Alps, 1801.  This is a distinct species with horizontally arranged branches, small, roundish, three-lobed leaves, and white flowers arranged in umbel-like corymbs.  It flowers in May, and is quite hardy.