Petals pink to purplish, as long as or longer than the sepals Lythraceae
Flowers regular; hypanthium without swelling or spur at the base
Hypanthium narrow-tubular Lythrum
Erect, often pubescent perennial 50–100 cm high. Leaves opposite, lanceolate, 2–5 cm long, slightly stem-clasping. Flowers 10–12 mm long, in a terminal leafy spike. Floral tube 5 mm long. Petals 5–6, c. 8 mm long, pink to purple or bluish. Stamens usually 12; 6 longer than the others, exserted. Widespread. Damp places. Fl. spring–summer. Purple Loosestrife Lythrum salicaria
Decumbent or ascending, weak, glabrous annual. Leaves mostly alternate, linear to elliptic, 5–10 mm long. Flowers small, solitary, nearly sessile in most of the axils. Floral tube 2–3 mm long, increasing to c. 6 mm in fruit. Petals 1–4 mm long, pale purplish or bluish. Widespread. Wet places. Fl. spring–summer Lythrum hyssopifolia