7. Phlox paniculata L. (perennial phlox, summer phlox, garden phlox)

Pl. 493 d–f; Map 2258

Plants perennial herbs with short, thick rhizomes. Vegetative stems not produced or, if present, then similar to the flowering ones. Stems typically 3–7 (more in cultivated forms), 70–120 cm tall, erect, with 20–35 nodes, glabrous toward the base, grading to sparsely to densely pubescent above the midpoint with short, curved, usually nonglandular hairs, sometimes with red streaks. Leaves all opposite or sometimes the uppermost subopposite, the blade narrowly elliptic to oblong-lanceolate, angled or more commonly tapered to a sharply pointed tip, variously angled or tapered at the base, the uppermost sometimes ovate, those of the largest leaves 9–14 cm long and 20–40 mm wide, the upper surface usually glabrous, the undersurface glabrous or less commonly sparsely short-hairy, the margins short-hairy, the secondary veins forming closed loops. Inflorescences with mostly 35 to more than 200 flowers, consisting of clusters or small panicles, the aggregate of clusters usually appearing as broad, domed to hemispheric or pyramidal panicles, occasionally narrower and appearing somewhat racemelike. Flower stalks 2–8 mm. Calyces 6–10 mm long, the lobes slender, tapered evenly to sharply pointed tips, glabrous or pubescent with short, nonglandular hairs. Corollas bright pink to light pinkish purple, purple, or light purplish blue, rarely white, the tube 18–25 mm long, sparsely to densely hairy externally, lacking a basal constriction, the lobes 6–12 mm long and 4–11 mm wide, obovate to broadly obovate, rounded at the tips, occasionally with a very shallow apical notch. Stamens with the filaments 15–21 mm long, the anthers positioned from below to at or above the stigma near the mouth of the tube (occasionally 1–3 slightly exserted). Style 12–24 mm long, the stigmas 0.8–1.3 mm long. 2n=14. June–September.

Scattered south of the Missouri River and in the northeastern quarter of the state (eastern U.S. west to Missouri and Louisiana; introduced farther north and west, also Canada). Bottomland forests, mesic upland forests, banks of streams and rivers, bases of bluffs, and fens; also roadsides and shaded, disturbed areas.

Phlox paniculata is the most commonly cultivated species in midwestern gardens. Some of the Missouri populations undoubtedly arose as escapes from gardens or compost. Many cultivars have been developed. Steyermark (1963) noted that although the wild species inhabits mostly shaded sites, the horticultural variants frequently tolerate full sunlight. Rare plants with white corollas have been called f. alba, but this epithet does not appear ever to have been officially published as a forma.