26. Spiraea L. (spiraea)

Plants shrubs, often colonial from rhizomes and/or root sprouts. Stems ascending or less commonly strongly arched, branched or unbranched, unarmed. Twigs glabrous or hairy, the winter buds small, with 2 to several overlapping scales. Leaves alternate, sessile or short-petiolate. Stipules absent. Leaf blades simple, unlobed, variously shaped, the margins simply or less commonly doubly toothed. Inflorescences axillary clusters or small umbels, or terminal panicles, the flowers relatively small, with a small linear bract along the stalk. Flowers perigynous, the hypanthium cup-shaped to somewhat conic, with a usually prominent nectar ring, glabrous or hairy on the outer surface. Sepals 5, spreading to ascending at flowering, triangular, persistent at fruiting or shed after flowering. Petals 5, broadly obovate to nearly circular, white or pink. Stamens 15 to numerous (except in doubled flowers), the anthers white or pink. Pistils 5 (except in doubled flowers), free. Ovary superior, glabrous or hairy, with 1 locule and 2 to several ovules. Style 1 per pistil, persistent, the stigma more or less capitate. Fruits follicles, ascending, elliptic-ovate in outline, tapered to an erect beak at the tip, glabrous or hairy, tan to brown and leathery to papery at maturity, dehiscing along the inner suture and also partially along the outer (dorsal) suture, 1–4-seeded. Seeds 1.5–2.5 mm long, narrowly ellipsoid, the surface with faint longitudinal lines or a fine network of slender ridges and quadrangular pits, yellowish to reddish brown. Seventy to 120 species, North America, Europe, Asia.

A number of species of Spiraea are cultivated as ornamental shrubs. Although the individual flowers are small, they are often produced in profusion.