4. Vinca L. (periwinkle)

(Stearn, 1973)

Plants perennial herbs, sometimes somewhat woody at the base, the sap not milky. Stems prostrate, forming dense mats, not twining, sometimes with loosely ascending branches or scrambling on other plants, occasionally climbing up tree trunks, rooting at the nodes. Leaves opposite, petiolate or rarely sessile. Leaf blades ovate-triangular or ovate to narrowly lanceolate, glabrous or pubescent with nonglandular hairs, rounded to angled or slightly tapered to a bluntly or sharply pointed tip, sometimes with a minute, abrupt, sharp point at the tip, angled, rounded, truncate, or shallowly cordate at the base, the main veins and adjacent tissue sometimes appearing whitened or lighter green on the upper surface, glabrous on both surfaces (the margins sometimes hairy). Inflorescences of solitary axillary flowers. Calyx lobes narrowly triangular to linear, sharply pointed at the tip, glabrous. Corollas trumpet-shaped, lacking appendages but usually with a narrow ridge or slightly thickened band around the tip of the tube (along the base of the lobes), the tube funnel-shaped, blue or bluish lavender, rarely white, hairy on the inner surface near the stamens, the lobes slightly shorter than to longer than the tube, spreading, often somewhat asymmetrical toward the tip. Stamens attached toward the midpoint of the corolla tube, the anthers incurved but free from and positioned above the stigma, narrowly obovate, hairy. Nectar glands 2, positioned on opposite sides of the ovary bases. Style gradually broadened toward the tip, the stigma more or less conical, with a narrow, disklike rim or wing of tissue at the base and minute tufts of hairs at the tip and base. Fruits rarely produced, 2–7 cm long, erect or ascending, relatively stout, narrowed or tapered above and below the seed(s), dehiscing longitudinally only with age. Seeds 1(2–5) per fruit, 3–7 mm long, mostly narrowly elliptic-ovate in outline, flattened, with a deep, longitudinal groove (the lateral margins appearing somewhat inrolled), the surface otherwise finely wrinkled, glabrous, dark brown to nearly black. About 6 or 7 species, Europe, adjacent southwestern Asia, northern Africa; widely escaped from cultivation in temperate and subtropical regions elsewhere.