Identification key to the Malagasy species of Catharanthus

1. Plants prostrate, stems spreading with pseudo-dichotomous branching, forming a rosette; flowers typically present at each node, always solitary. (Restricted to the sub-arid south).................. C. scitulus (Pichon) Pichon

1a. Plants more or less erect, stems ascending, poorlybranched, never appearing pseudo-dichotomous; flowers generally localised at the extremities of the branches, solitary or in pairs. (Widely distributed, but generally absent from the sub-arid south)........................ 2

2. Stems clearly angular, square or hexangular in section.. 3

2a. Stems cylindrical sometimes with four shallow longitudinal ridges, round or elliptic in section................. 5

3. Leaves subsessile; stems square in section; corolla with a white to yellow eye and fuchsia pink to mauve-pink lobes. (Unknown from the Makay Massif)............... 4

3a. Leaves with petioles ca. 2 mm long; stems hexangular in section; corolla with a magenta eye and white (or faintly pink-tinted) lobes. (Endemic to the Makay Massif).. C. makayensis L. Allorge, Phillipson & Razakamal.

4. Stems and leaves glabrous; leaves oval, more or less amplexicaule at the base. (Common in the southern part of the Central Plateau and extending to the Isalo Massif and with scattered localities in the south-west)................................ C. ovalis Markgr.

4a. Stems and leaves pubescent; leaves lanceolate, cuneiform at the base (throughout the northern areas of Madagascar, extending down the east coast at least as far asFarafangana)....... C. trichophyllus (Baker) Pichon

5. Plants relatively large at maturity, at least 30 cm (sometimes reaching 100 cm) high; leaves mostly more than 30 mm long; inflorescence mostly 2-flowered; follicles always erect.................................. 6

5a. Plants relatively small at maturity, rarely more than 30 cm high; leaves generally less than 30 mm long; inflorescence 1-flowered; follicles erect or pendulous............. 7

6. Leaves ovate, generally more than 10 mm wide, apex obtuse and mucronate, margins flat; corolla typically pink with a magenta eye or white with a yellow eye (in C. roseus var. albus G. Don). (Naturally limited to the south-eastern Madagascar, but cultivated and naturalized in Madagascar, as well as throughout the tropics).. C. roseus (L.) G. Don

6a. Leaves lanceolate, less than 9 mm wide, apex acute, margins generally revolute; corolla pink with a yellow eye, lobes white at the very base. (Upland areas in the South-east from Andringitra to the Mandrare Bassin)................................ C. longifolius (Pichon) Pichon

7. Foliage relatively dense, the leaves longer than the internodes; follicles becoming pendulous due to the elongation of the pedicels after anthesis. (Mainly in and around the Itremo Massif, but with scattered sub-populations from the Tampoketsa west of Antananarivo, and on the inselbergs around Ambalavao)......... C. coriaceus Markgr.

7a. Foliage relatively sparse, the leaves generally shorter than the internodes; follicles always erect, pedicels hardly elongating after anthesis. (Common around Antananarivo and south towards Fianarantsoa)...................................... C. lanceus (Bojer ex A. DC.) Pichon