According to the latest revision (van Bergen, 1996), Catharanthus roseus may be distinguished from the other seven species of Catharanthus by a combination of characters including its perennial, usually shrubby habit, with cylindrical rather than quadrangular stems; broad, petiolate leaves; and a corolla tube usually over 22 mm long with lobes usually over 10 mm long. This species was formerly placed within the genus Vinca; Vinca as it is now defined includes only herbaceous plants with funnel-shaped corollas and anthers borne on elongated filaments.
van Bergen, M. A. 1996. Revision of Catharanthus G. Don. Series of revisions of Apocynaceae XLI. Wageningen Agricultural University Papers 96-3: 9-46.
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