Voacanga

Jongkind, Carel C. H. & Lachenaud, Olivier, 2022, Novelties in African Apocynaceae, Candollea 77 (1), pp. 17-51 : 45-46

Voacanga

Voacanga is a Paleotropical genus of trees and shrubs, belonging to tribe Tabernaemontaneae , subtribe Tabernaemontaninae ( ENDRESS et al., 2018) and closely related to Tabernaemontana (see above). The genus was last revised by LEEUWENBERG (1985), who recognised 12 species, seven of which occur in Africa (one of them also in Madagascar) and five in Asia.

Some of the African species as currently delimited are very variable, in particular Voacanga bracteata Stapf , supposedly a widespread species with a disjunct distribution in West and Central Africa. A reexamination of herbarium material showed that collections included in this species by LEEUWENBERG (1985) represent four different taxa. One of them is endemic to West Africa and represents V. bracteata s.str. Central African specimens previously referred to that species belong in majority to two taxa elevated here at specific rank, V. lanceolata (Stapf) Jongkind ( V. bracteata var. lanceolata Stapf ) and V. diplochlamys K. Schum. ; a complete description of the latter is presented here since the original one ( SCHUMANN 1895: 149) is extremely brief. Finally, the type of V. micrantha Pichon , included in V. bracteata by LEEUWENBERG (1985), is also distinct from the aforementioned species and probably represents V. psilocalyx Pierre ex Stapf.

Apart from these changes, the new species Voacanga cornuta Jongkind from Gabon is described. The genus now includes 15 species, 10 of which are African. In addition, CHEEK et al. (2004: 245) mentioned a “probably new species” of Voacanga ( Voacanga sp. 1 ) from south-west Cameroon, the material of which we have not seen; it apparently differs from most other species of the genus by its connate carpels (also found in V. chalotiana Pierre ex Stapf ).

suborbicular to broadly ovate elliptic or ovate, elliptic or ovate,

Calyx lobes

(length ≤ width) longer than broad longer than broad

Corolla tube length

13–18, white 50–80, (pale) green 9–14, (pale) green

and colour [mm]

Corolla lobe length [mm] 13–20 25–50 7–17

Indumentum of corolla lobes glabrous except left margin glabrous or puberulous basally puberulous basally on both sides narrowly ovoid and broadly narrowly ovoid, narrowly winged, broadly ovoid, bumpy, Fruit shape winged, otherwise smooth otherwise smooth ( Fig. 14A ) not winged ( Fig. 14B ) ( Fig. 14C )

Fruit colour yellow to orange yellow to orange pale bluish-green Distribution Guinea to Ghana Sierra Leone to Ghana Nigeria to Gabon

Voacanga bracteata Stapf in Bull. Misc. Inform. Kew 1894: 22. 1894 ( Fig. 16A, B ).

Lectotypus (designated by LEEUWENBERG, 1985: 22): SIERRA LEONE. Southern Prov.: River Bagroo , IV.1861, fl., Mann 858 (K [K000233603]!)

Distribution and ecology. – Sierra Leone, south-eastern Guinea, Liberia, Côte d’Ivoire and Ghana ( Fig. 15B ), growing in forest from near sea-level to elevations of 610 m.

Notes. – This species is here regarded as a West African endemic; specimens from Central Africa and Nigeria referred to Voacanga bracteata by LEEUWENBERG (1985) belong to V. lanceolata (mostly), V. diplochlamys and V. psilocalyx . Differences between the four species are summarised in Table 7. An unusual character of V. bracteata and V. lanceolata , not seen in other species of the genus, is that their corolla lobes change, during flowering, from spreading and cream coloured to reflexed and shiny brown (the corolla seeming still to expand in this process) ( Fig. 16C ).

Figures

Fig. 14. – Fruit carpels of Tabernaemontana L.: A. Tabernaemontana fragrans Jongkind; B. Tabernaemontana psorocarpa (Pierre ex Stapf) Pichon. C. Tabernaemontana glandulosa (Stapf) Pichon. Flowers of Tabernaemontana: D. Tabernaemontana psorocarpa; E. Tabernaemontana glandulosa; F.Tabernaemontana fragrans.

Fig. 16. – Voacanga bracteata Stapf: A. Inflorescence showing

Fig. 15. – Distribution maps. A. Tabernaemontana fragrans Jongkind (circles) and T. psorocarpa (Pierre ex Stapf) Pichon (triangles). B. Voacanga bracteata Stapf. C. Voacanga cornuta Jongkind (stars) and V. diplochlamys K. Schum. (circles).