Subshrub or herb (15–)30–100(–200) cm high, erect or decumbent; base usually woody with pale gray bark; latex white.  Stems terete, longitudinally ridged or narrowly winged, green or dark red, pubescent at least when young.  Leaves decussate, stipulate; stipules 2–4, acuminate, <1(–2) mm long; petiole (1–)3–11 mm long, narrowly winged, green or red; blade (1.0–)2.5–9.0 x (0.6–)0.8–4.0 cm, elliptical to obovate, oblong, or rarely lanceolate; apex mucronulate, rounded to acute or obtuse; base cuneate to attenuate; margins entire, sometimes ciliate; venation pinnate with 7–11 pairs of lateral veins; both surfaces dark green with pale lateral veins in living material; petiole, stipules, and blade pubescent or glabrous.  Inflorescences axillary; flowers paired on peduncles 1–4 mm long or solitary, subsessile; inflorescence pubescent or glabrous.  Sepals 5, 2–6 mm long, basally connate, narrowly triangular, subulate, pubescent or glabrous.  Corolla salverform; tube usually greenish, (1.5–)2.2–3.0 cm long, externally glabrous or pubescent, internally pubescent with strigose rings below mouth and below insertion point of stamens; lobes 5, pink to white or reddish purple, often with a darker or yellowish center, (0.5–)1.0–2.8 cm long, broadly obovate with narrowed base and rounded, usually cuspidate apex, sometimes pubescent.  Stamens 5, inserted in widest upper portion of corolla tube; anthers subsessile, 2.2–3.0 mm long, narrowly triangular, included within corolla tube.  Gynoecium of 2 free carpels below, syncarpous above; ovary pubescent or glabrous; single style 15–24 mm long; terminal pistal head bearing a recurved basal veil, pubescent ring, and pubescent cylinder with bilobed stigma; disk of 2 glands, 2–4 mm long, alternating with carpels.  Fruit 2 follicles, (1.2–)2.0–4.7 cm long, linear-terete, erect, longitudinally ridged, green, pubescent or glabrous; seeds numerous, black, 1–3 mm long, irregularly oblong.

References

Forster, P. I. 1996. Apocynaceae. Fl. Australia 28: 104-196.

Li P.-T., A. J. M. Leeuwenberg and D. J. Middleton. 1995. Apocynaceae. Pp. 143–188 in Wu Z.-Y. and P. H. Raven, eds., Flora of China vol. 16. Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis, MO.

Markgraf, F. 1976. Apocynacées. Fl. Madagascar 169: 1-318.

Plaizier, A. C. 1985. Catharanthus. Fl. Zambesiaca 7(2): 453-456.

van Bergen, M. A. 1996. Revision of Catharanthus G. Don. Series of revisions of Apocynaceae XLI. Wageningen Agricultural University Papers 96-3: 9-46.