Plants perennial. Stems erect or ascending, 1–5(–7) dm. Leaves opposite (whorled); blade linear-lanceolate to lanceolate or elliptic, 8–15(–20) × 2–6 mm. Pedicels ascending in fruit, 20–50 mm, longer than subtending leaf. Flowers: sepals 5, calyx divided to ca. 1/2, 4–6 mm, shorter than corolla, margins entire, narrowly scarious, apex acute to acuminate; petals 5, corolla blue or red, salverform (almost rotate) to slightly campanulate, 5–12 mm. Capsules 5–7 mm. Seeds 20–45. 2n = 22 (Europe).
