Voacanga cornuta Jongkind, 2022

Jongkind, Carel C. H. & Lachenaud, Olivier, 2022, Novelties in African Apocynaceae, Candollea 77 (1), pp. 17-51 : 46-50

Voacanga cornuta Jongkind , sp. nov. ( Fig. 17 ).

Holotypus: GABON. Woleu-Ntem: Nzec , 9.XI.1933, fl., Le Testu 9385 ( BR [ BR0000014685156 ]!; iso-: P [P03859514, P03859516, P03859517] images!, WAG [ WAG.1667822]!) .

Voacanga cornuta Jongkind resembles V. pachyceras Leeuwenb. by the shape of its fruits and the presence of a short dense indumentum on the lower side of the leaves, but differs by its smaller calyx (10 mm long vs. 15–22 mm long) and shorter corolla lobes (7–8 × 3.5 mm vs. 10–22 × 4–15 mm).

Treelets (?). Twigs cylindrical, glabrous. Leaves opposite, entire; blade 7– 18 × 1.5 –6 cm, narrowly elliptic or oblong, attenuate at base, acuminate at apex, glabrous above, beneath with many inconspicuous, colourless, tiny, erect hairs; 7–9 pairs of main lateral veins, tertiary venation inconspicuous; petiole 1–2 cm long, with tiny hairs below. Inflorescences terminal and paired, few-flowered, peduncle slender, 3.5–7 cm long, with scattered tiny hairs; bracts up to 7 × 5 mm, glabrous, apex rounded. Flowers 5-merous; pedicel 5–6 mm long, (almost) glabrous. Calyces 10 mm long, colleters scattered inside tube, lobes 5 mm long and wide, acute to rounded at apex. Corollas exceeding calyx, tube c. 21 × 4 mm, lower half conspicuously twisted, gradually narrowed to throat, glabrous outside, inside with a pubescent belt from a few mm above base to insertion of stamens, lobes 7– 8 × 3.5 mm, elliptic with rounded apex, glabrous, spreading, in bud forming an almost conical head c. 2 times as long as wide, with a blunt apex. Stamens included but apex close to corolla mouth, glabrous, anthers c. 5.5 mm long, subsessile, sagittate at base, acuminate at apex. Pistils 9 mm long, glabrous; ovary c. 1 mm high, with two the inside of the calyx with more or less scattered colleters near the base; B. Fruits. Voacanga lanceolata (Stapf) Jongkind : C. Inflorescence including flower with reflexed, brown lobes.

[A: Jongkind 14161; B: Jongkind 13349; C: Droissart 1627]

[Photos: A, B: C.Jongkind;C: V.Droissart]

[A–F: Le Testu 9385; G: Le Testu 9040] [Drawing:A. Fernandez]

free carpels; disk annular; pistil head with a ring connecting it to stamens. Fruits of two separate, narrowly ellipsoid, mericarps; mericarps 3–5 × 0.6–1 cm, acute at apex, many seeded, glabrous. Seeds dark brown, obliquely ellipsoid, 6.5–8 × 3 mm, with a minute tuberculate structure.

Distribution, ecology and phenology. – This species is only known from north-eastern Gabon, but might be expected in adjacent Cameroon and Equatorial Guinea ( Fig. 15C ); the habitat is not recorded, but presumably, corresponds to lowland evergreen rainforests. Flowers have been collected in November, during the main rainy season, and fruits in March, during the second dry season.

Conservation status. – Voacanga cornuta is known from two collections made in the 1930s in north-eastern Gabon, representing two occurrences, both of which are considered still extant since forest cover is still present in these areas. Based on a 2 × 2 km cell size, its Area of Occupancy [AOO] is estimated as 8 km ², which falls under the threshold for “Critically Endangered” status under Criterion B2. Its Extent of Occurrence (EOO) cannot be calculated. The two occurrences represent two subpopulations. One occurrence is located within a logging concession, and is threatened by forestry, that induces a decline in its habitat extent and quality. The other occurrence near Bitam is threatened by small scale agriculture, urbanisation and industrial oil palm plantations that are occurring in the area, all of which also inducing a decline in the extent and quality of its habitat. The two occurrences represent two locations (sensu IUCN, 2019) with regard to the most serious plausible threats (small-scale agriculture, urbanisation and industrial oil palm plantations). We infer a past, present and future continuing decline in the habitat extent and quality of this species. Therefore, V. cornuta qualifies for an “Endangered” status [EN B2ab(iii)]. New searches are required in its area of occurrence to better document its distribution and state of conservation. The absence of recent collections would be explained when V. cornuta proves to be an understory species of the closed forests that is not growing in roadsides or near forest edges.

Notes. – This species closely resembles Voacanga pachyceras , which in addition to characters listed in the diagnosis also differs in its distribution, being only known from D.R. Congo with its closest occurrences c. 900 km to the south-east of the range of V. cornuta .

The two collections of Voacanga cornuta were not previously recognised as conspecific. The flowering specimen Le Testu 9385 was cited in the revision of Voacanga (LEEUWENBERG, 1985) as V. psilocalyx , which differs from V. cornuta in its glabrous leaves and broader, widely divergent mericarps. The fruiting specimen Le Testu 9040 was cited in the Tabernaemontana revision ( LEEUWENBERG, 1991) as T. hallei (Boiteau) Leeuwenb. This latter species has a glabrous lower leaf surface, almost sessile inflorescences, and a shorter calyx with free sepals persistent under the fruit; its corolla is also much larger (similar to that of T. glandulosa illustrated in Fig. 14E ) and therefore any confusion is unlikely in the flowering stage.

Additional specimen examined. – GABON. Woleu-Ntem: Bitam , 17.III.1932, fr., Le Testu 9040 ( BR, P, WAG) .

Voacanga diplochlamys K. Schum. in Engl. & Prantl, Nat. Pflanzenfam. 4(2): 149. 1895.

Lectotypus (designated by LEEUWENBERG, 1985): CAMEROUN. South-West Region: Barombi , 11.III.1889, fl., Preuss 14 (K [K000233602]!) .

= Voacanga talbotii Wernham, Cat. Pl. Oban : 63. 1913. Holotypus: NIGERIA. Cross River State: Oban, fl., Talbot 1624 (BM [ BM000925740 ]!).

Shrubs or treelets, 2–6 m tall, with abundant white latex. Twigs cylindrical, 1 –3.5 mm thick, glabrous, soon covered with dark brown bark. Leaves opposite, entire; blade elliptic to narrowly oblong, 6–22 × 2–9.5 cm, cuneate at base, gradually acuminate at apex, glabrous above, minutely puberulous on midrib and lateral veins below; midrib channelled above, prominent below; secondary veins (8–)10– 16 pairs, ascending and almost straight, forming inconspicuous loops close to margin; tertiary veins invisible or very lax; petiole 1–2 cm long, minutely puberulous. Inflorescences terminal, solitary or paired, umbellate to laxly cymose, ± drooping, 5 –12 cm long, 4 – 20-flowered, densely puberulous, with peduncle 4 – 9 cm long and ramifications up to 2.5 cm long; bracts usually persistent at anthesis, sometimes caducous, ovate to obovate, 6–8 × 3–6 mm, acute to rounded at apex, puberulous outside. Flowers 5-merous; pedicel 4–8 mm long, glabrous to densely puberulous. Calices pale green, 12–19 mm in diam., tube campanulate, 5–6 × 5.5–7 mm, glabrous or puberulous at base outside, provided inside with a discontinuous band of colleters around mid-height, lobes elliptic to obovate, 4–8 × 3–8 mm, rounded at apex, spreading or (usually) reflexed at anthesis, glabrous. Corollas yellow, 7–10 mm in diam., tube 10–12 × 5 mm, slightly longer to slightly shorter than calyx, constricted at throat and a little above mid-height, strongly twisted especially in upper half, glabrous outside, inside with dense band of short appressed pubescence below anthers, lobes obovate, 3.5–7 × 2.5– 4 mm, 1.4– 1.75 times as long as broad, rounded at apex, patent or reflexed at anthesis, glabrous; anthers included with their tips just reaching corolla throat, attached on corolla tube at around 3/5 of its length from base, subsessile, sagittate, c. 4 mm long, acute at apex, glabrous, with straight tails, coherent and forming a cone around pistil head. Pistils 8–10 mm long; ovary ± hemispherical, c. 1.7 mm long, glabrous, with two free carpels closely appressed against each other; disk annular, c. 1 mm long; style glabrous, c. 6 mm long, narrowly cylindrical, pistil head with saucer-shaped base c. 0.7 × 2 mm and pentagonal domed apex c. 0.7 × 1.2 mm. Fruits (immature) green, consisting of two separate mericarps, these obovate, 3–4 × 2.2–2.5 cm, rounded at apex, glabrous.

Distribution, ecology and phenology. – This species occurs in south-eastern Nigeria, Cameroun, Equatorial Guinea ( Rio Muni) and north-eastern Gabon ( Fig. 15C ) and grows in primary evergreen and secondary regrowth forests, at elevations of 150– 760 m. Flowers have been collected mostly from January to March, and in September and October; immature fruits in April, May and October.

Notes. – This species was included by LEEUWENBERG (1985) in the synonymy of Voacanga bracteata , and the specimen Brenan 9300 was also cited under the latter by CABLE & CHEEK (1998). However, the two taxa differ in numerous characters ( Table 7) and may be separated even in the vegetative state. The corolla of V. diplochlamys is always reported by collectors to be yellow, and thus does not seem to turn brown after anthesis as in V. bracteata and V. lanceolata . The inflorescence bracts of V. diplochlamys are usually persistent at anthesis, as in V. bracteata , but may occasionally be caducous. Fruits are still imperfectly known, only three immature ones have been seen (Cheek 11571, Esono 17, Etuge & Thomas 27).

Additional specimens examined. – NIGERIA. Akwa Ibom State: Eket district, 1912–13, fl., Talbot s.n. ( BM [2 sheets]) . Cross River State: Old Calabar, s.d., fl., Robb s.n. ( BM) .

CAMEROUN. Central Region: Ndanan 1- Ndangan 1, 9.III.2004, fl., imm. fr., Cheek 11571 ( BR, K, WAG); c . 5 km S of M’Balmayo, 2.II.1964, fl., W.J.J.O. de Wilde & de Wilde-Duyfjes 1801 ( BR, K, P, WAG); Makak , X.1938, fl. & imm. fr., Jacques-Félix 2260 (P); c . 10 km S of M’Balmayo , 9.III.1978, fl., J. Lowe 3565 (K) . South Region: 72 km on the road from Ebolowa to Ambam , 16.I.1975, fl., J.J.F.E. de Wilde 7905A ( MO, WAG) ; Akonetye , 17.I.1978, fl., Koufani 60 (P, WAG) ; près Ngom, 40 km SSE Ebolowa , 2.II.1970, fl., Letouzey 9968 ( BR, K, P, WAG); c . 2 km S of Kwambo and 6 km WSW of Bipindi, 19.I.1987, fl., Manning 1461 ( MO, WAG) ; Nkoemvone, 13.II.1963, fl., Raynal 9594 (P); Campo-Ma’an area, Onoyong , 18.III.2001, fl., Tchouto Mbatchou ONOX 85 ( WAG) ; Campo-Ma’an area, Mvini , 19.II.2000, fl., Tchouto Mbatchou 2625 ( WAG) ; Bebai, Campogebiet, 30.X.1908, fl., Tessmann 601 (K); Bipindi , 1911, fl., Zenker 4163 ( BM, G, K) . South-West Region: Mbalange N.A. Forest Reserve, Southern Bakundu, 16.I.1956, fl., Binuyo & Daramola FHI 35051 (K, P); Banga, S Bakundu F.R., 11.III.1948, fl., Brenan 9300 (K); near Ngombombeng village , N of Nyassosso , 31.IV.1986, imm. fr., Etuge & Thomas 27 ( BR, WAG) ; R.F. d’Ejagham, 29.IX.1984, fl., Onana 85 (P, WAG) ; R.F. d’Eyumojock, 14.II.1985, fl., Onana 182 (P, WAG) ; Abonando, 15.III.1902, fl., Rudatis 14 (K); near Kumba , 17.II.1985, fl., Thomas & Nemba 4394 (K, MO, P, WAG) .

Petiole and lower side

glabrous puberulous

of leaf veins

Secondary leaf veins 6–10 pairs (8–)10–16 pairs

Inflorescences glabrous puberulous glabrous glabrous

6–10 pairs (4–)6–12 pairs glabrous glabrous forming a dense band forming a sparse band Colleters inside calyx forming a more or less forming a sparse band near the base ( Fig. 16C ; around mid-height tube dense band near the base around mid-height Leeuwenberg 1985: 23, or near the base fig. 2, 4)

spreading or (usually)

Calyx lobes erect erect or oblique erect

reflexed

(1.5–)2–4 × longer

<1.5 × longer than broad, 1.4–1.75 × longer than <1.5 × longer than broad,

Shape of corolla lobes than broad, elliptic obovate broad, obovate obovate

to narrowly obovate pale yellow turning dark pale yellow turning dark white to pale yellow, Colour of corolla lobes yellow, not turning brown brown brown not turning brown Orientation of corolla patent, or reflexed reflexed at maturity reflexed at maturity reflexed at maturity lobes only at apex

Fruit colour yellow to orange?

Monocarp shape half moon-shaped obovate pale green to cream-

yellow to orange coloured half moon-shaped subglobose

to ovoid

Distribution Sierra Leone to Ghana Nigeria to Gabon Nigeria to D.R. Congo Nigeria to D.R. Congo

EQUATORIAL GUINEA. Centre Sur: c. 700 m from ECOFAC-Hotel, 1.III.1998, fl., J.J.F.E. de Wilde et.al. 12046 ( WAG) . Wele-Nzas: Piedra Nzás , 23.V.1998, imm. fr., Esono 17 ( BRLU) ; entre Nsuameyong et inselberg Akuom , 16.I.1998, fl., Obama & Lejoly 413 ( BRLU) .

GABON. Woleu-Ntem: Oyem , 21.IX.1933, fl., Le Testu 9399 ( BM, P, WAG) .

Voacanga lanceolata (Stapf) Jongkind , comb. et stat. nov. ( Fig. 16C ).

 Voacanga bracteata var. lanceolata Stapf, Fl. Trop. Afr. 4(1): 161. 1902.

Lectotypus (designated by LEEUWENBERG, 1985: 22): CAMEROUN. Central Region: Yaoundé, 1896, fl., Zenker 694b (K [K000233768]!; isolecto-: S image!, WU image!) .

Distribution and ecology. – A widespread and relatively common species in south-eastern Nigeria, Cameroun, Equatorial Guinea, Gabon, Republic of Congo and Democratic Republic of Congo, in forests up to elevations of 1200 m.

Notes. – This species, originally described as a variety of Voacanga bracteata , is here elevated at species rank; for more information see the Notes section under V. bracteata .

Figures

Fig. 17. – Voacanga cornuta Jongkind. A. Flowering branch; B. Leaf from below showing indumentum; C. Flower (longitudinal section, calyx removed); D. Flower (opened) showing stamens and pistil; E. Calyx,inside showing colleters; F. Pistil; G. Fruit.

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).

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