S. DISCOLOR ARIAEFOLIA (syn S. ariaefolia).—­White Beam-leaved Spiraea.  North-west America, 1827.  This forms a dense, erect shrub about 6 feet high, with elliptic-oblong leaves, and clothed beneath with a whitish tomentum.  The flowers are in large, terminal, slender-stalked panicles, and white or yellowish-white.  It is one of the handsomest species in cultivation, the neat and yet not stiff habit, and pretty, plume-like tufts of flowers making it a general favourite with the cultivators of hardy shrubs.  Flowers about mid-summer.  In rich soils, and where partially shaded from cold winds, it thrives best.

S. DOUGLASII.—­Douglas’s Spiraea.  North-west America.  This has long, obovate-lanceolate leaves, that are white with down on the under surface, and bears dense, oblong, terminal panicles of rosy flowers.  S. Douglasii Nobleana (Noble’s Spiraea) is a variety of great beauty, growing about a yard high, with large leaves often 4 inches long, and looser panicles of purple-red flowers.  Flowering in July.  The variety was introduced from California in 1859.

S. FISSA.—­Split-leaved Spiraea.  Mexico, 1839.  A stout, erect-growing shrub, about 8 feet high, with rather small leaves, angular, downy branches, and long, loose, terminal panicles of small and greenish-white flowers.  The leaves are wedge-shaped at the base, and when young have the lateral incisions split into a pair of unequal and very sharp teeth.  Flowering in May and June.  In the south and west of England it thrives best.

S. HYPERICIFOLIA (syn S. flagellata).—­Asia Minor, 1640.  A wiry twiggy shrub, fully 4 feet high, with entire leaves, and small, white flowers produced in umbels at the tips of the last year’s shoots.  It is a pretty and desirable species.

S. JAPONICA (syns S. callosa and S.  Fortunei).—­Japanese Spiraea.  China and Japan, 1859.  This is a robust species about a yard high, with large lanceolate leaves, and small, rosy-red flowers arranged in corymbose heads.  Flowering at mid-summer.  There are several fine varieties of this species, including S. japonica alba, a compact bush about a foot high with white flowers; S. japonica rubra differs from the type in having dark red flowers; S. japonica splendens, is a free-flowering dwarf plant, with peach-coloured flowers and suitable for forcing; and S. japonica superba, has dark rose-red flowers.  S. Bumalda is a closely allied form, if not a mere variety of S. japonica.  It is of dwarf habit, with dark reddish-purple flowers.

S. LAEVIGATA (syns S. altaicensis and S. altaica).—­Smooth Spiraea.  Siberia, 1774.  A stout, spreading shrub about a yard high, with large, oblong-lanceolate, smooth, and stalkless leaves.  The white flowers are arranged in racemose panicles, and produced in May.

S. LINDLEYANA.—­Lindley’s Spiraea.  Himalayas.  A handsome, tall-growing species, growing from 6 feet to 8 feet high, with very large pinnate leaves, and pretty white flowers in large terminal panicles.  It is the largest-leaved Spiraea in cultivation, and forms a stately, handsome specimen, and produces its showy flowers in great quantities.  Flowering at the end of summer.