Hunteria

Jongkind, Carel C. H. & Lachenaud, Olivier, 2022, Novelties in African Apocynaceae, Candollea 77 (1), pp. 17-51 : 22-26

Hunteria

The genus Hunteria was revised by OMINO (1996), along with the closely related genera Picralima Pierre and Pleiocarpa Benth. These genera, together with Gonioma E. Mey. , form

[A: Bidault et al. 4363; B, D: Bidault et al. 5144; C: Bidault et al. 1398] [Photos: E. Bidault]

the tribe Hunterieae ( ENDRESS et al., 2018) . The members of this tribe are trees or shrubs displaying left-contorted corolla aestivation, absence of corona, anthers included and fertile to the base, absence of disk, and fleshy fruits with separate carpels. The great similarity between Hunteria , Picralima and Pleiocarpa suggests the need of merging them, though in the absence of phylogenetic data we have followed the traditional classification. Hunteria differs from Picralima by its smaller fruits with fleshy (not hard) pericarp, its seeds with membranaceous (not coriaceous) testa and cotyledons lacking secondary veins, and its sepals imbricate only in bud stage (vs. imbricate even at anthesis) ( OMINO, 1996). Differences with Pleiocarpa are discussed under the latter.

A new species of Hunteria is described here based on recent collections from Gabon. The genus now includes 13 species, all of which are African except for H. zeylanica (Retz.) Gard. ex Thw. that reaches Asia ( OMINO, 1996; ENDRESS et al., 2018).

Hunteria maasiorum Jongkind & E. Bidault , sp. nov. ( Fig. 4B, D, 5).

Holotypus: GABON. Estuaire: entre Kinguélé et Tchimbélé, au sud de Makaban, le long de la Bangoui, 0°31'N 10°17'E, 320 m, fl., 28.X.2020, Bidault et al. 5144 ( MO!; iso: BR!, BRLU!, G!, LBV!, MA!, P!, WAG!) .

Hunteria maasiorum Jongkind & E. Bidault resembles H. simii (Stapf) H. Huber in its laxly umbellate inflorescences, oblong monocarps ending in a long beak, and leaves with well-spaced and curved lateral veins, but differs by its conspicuously longer calyx lobes (4.5–6 mm vs. 1–1.3 mm), longer corolla lobes (12–16 mm vs. 7–12 mm) and larger seeds (17–24 × 11–13 × 5–8 mm vs. 11–15 × 6.5–8.5 × 5.5–6.5 mm).

Shrubs or treelets, up to 5 m tall. Leaves glabrous; blade elliptic, 17.5 – 25 × 6.8 – 10 cm, acute at base, acuminate at apex, slightly coriaceous; midrib narrowly channelled above; secondary veins 8–10 pairs, often with 1–3 less conspicuous secondary veins in between, ascending and slightly curved, forming a submarginal vein and an angle of 45 – 60° with midrib; tertiary venation inconspicuous; petiole 10– 15 mm long. Inflorescences terminal, sometimes axillary, glabrous except for corolla, umbellate, 3–10-flowered, with a peduncle 3–5 mm long. Flowers 5-merous, with pedicels 4–10 mm long. Calyx lobes 4.5–6 × 1–2 mm, gradually narrowing from base to apex, glabrous, with a row of small colleters inside at base, slightly spreading. Corollas white, in bud up to 28–30 mm long, glabrous outside; tube in open flower 16–21 × 2–4 mm, almost cylindrical with a slight widening at level of stamens, inside with sparse hairs around pistil head; lobes overlapping to the left, 12–16 × 3–7 mm, spreading, rounded at apex, entirely glabrous. Stamens included, inserted towards upper third of corolla tube; anthers 1.7–2.1 × 0.8–1 mm, subsessile, glabrous. Pistils c. 7 mm long, glabrous, not reaching base of stamens; ovary ovoid, c. 2 × 1 mm, style c. 3.7 mm long, pistil head ovoid with stigmoid apex, c. 1.3 × 0.7 mm. Fruits yellowish, smooth, glabrous, of two separate mericarps divergent at an angle of 180°, mericarp c. 7 × 2 cm, bluntly acuminate at apex. Seeds smooth, variable in shape but all flattened and more or less angular, 17–24 × 11–13 × 5–8 mm; embryo c. 1 cm long.

Etymology. – Hunteria maasiorum is named after Paul Maas and Hiltje Maas-van de Kamer, who discovered the species during an expedition to Gabon in 2011.

Distribution, ecology and phenology. – This species is endemic to the south-west of the Cristal Mountains in northern Gabon ( Fig. 6 ), where it occurs in the understory of wet evergreen forests, both mature and degraded, at elevations of 35– 330 m. It appears to favour rocky areas with an open understory, often along rivers, but has also been collected on drained soils. Flowers have been collected in October and November, and fruits in November, corresponding to the main rainy season.

Conservation status. – Hunteria maasiorum is known from seven collections made between 2011 and 2021, all from the Monts de Cristal area, in Gabon. All the occurrences are considered extant considering the still important forest cover in those areas, and the recent dates of collection. Based on a 2 × 2 km cell size, the AOO of this species is estimated as 28 km ², below the upper threshold for “Endangered” status under Criterion B2. The EOO is calculated as 62 km ², below the upper threshold for “Critically Endangered” status under Criterion B1. Two collection sites are located within the Monts de Cristal National Park, sector Mbé. Two other occurrences are located within a logging concession, and are threatened by activities linked with logging, inducing a decline in its habitat quality. Two collection sites, situated outside the National Park at its southern tip, are within the construction site of a planned hydro-electric project, and therefore threatened by it. We expect this location will disappear in the future. One collection site situated within the NP is nonetheless within the projected inundated area resulting from the dam project. It is therefore also threatened by it, and expected to disappear in the future. The other site located within the Monts de Cristal NP does not show any evidence of threat. The last site is situated outside the NP, between a road and a power line, and is threatened by the maintenance of those infrastructures that involves a degradation of its habitat quality. As a consequence, these six occurrences represent four locations (sensu IUCN 2019), with regard to the most serious plausible threat (hydro-electric projects), under the upper limit for “Endangered” status. We infer a past, current, and future continuous decline in the extent and quality of habitat consequently to all the threats above mentioned. We also infer a future decline in

10 cm 1 cm

C 5 mm E A

D B 5 mm 1 mm G 5 cm F 1 cm 1 cm I H

[A–F: Maas et al. 9964; G–I: Maas et al. 10415] [Drawing: H. de Vries]

the EOO, AOO, number of locations and number of mature individuals of this species, due to the hydro-electric project. This species is thus assigned a status of “Endangered” [EN B1a b(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)].

Notes. – This is a very distinctive species when fertile, with its large calyx and corolla (the largest recorded in the genus) and narrow beaked mericarps. Its closest relative is presumably Hunteria simii , which in addition to the differences mentioned in the diagnosis has a widely separate distribution, being found from Sierra Leone to Côte d’Ivoire. Other species of Hunteria have a much smaller corolla (tube ≤ 13 mm long, lobes ≤ 8.8 mm long) and calyx lobes (≤ 2.5 mm long), and mericarps globose to broadly ovoid (although fruits of H. densiflora Pichon and H. myriantha Omino are not yet known). In addition, most of them have the secondary leaf veins more numerous and almost straight, forming a broader angle with the midrib; except for H. myriantha and H. hexaloba (Pichon) Omino which are similar to H. maasiorum in this respect.

In the flowering stage, Hunteria maasiorum could be mistaken for Petchia africana Leeuwenb. , which has a very similar inflorescence, calyx and corolla, except that the latter is bright yellow. The leaves of P. africana are more abruptly cuspidate at the apex and have more numerous secondary leaf veins (12–20 pairs) forming an almost straight angle with the midrib. The long moniliform mericarps of Petchia are very different from those of Hunteria .

In vegetative characters, Hunteria maasiorum is very similar to H. hexaloba and Pleiocarpa robusta (described below), but these two species have the leaf midrib not channelled above but somewhat prominent. They also differ in their subsessile flowers, much smaller calyx, and shortly ovoid mericarps.

Additional specimens examined. – GABON. Estuaire: Monts de Cristal, Kinguélé , vallon à l’Ouest de la Mbé, 0°24'03"N 10°15'18"E, 19.IV.2021, fl., Bidault et al. 5326 ( LBV, MO) ; Monts de Cristal , site du chantier du barrage hydroélectrique de Kinguélé Aval, 0°23'N 10°14'E, 19.XI.2020, st., Klein et al. 38 ( BRLU, LBV) ; Monts de Cristal, à l’est de la route Kinguélé-Andok Foula , 106 m, 0°24'N 10°14'E, 24.X.2020, fl. buds [very young], Lachenaud et al. 3139 ( BRLU, LBV, MO) ; Parc National de Monts de Cristal, road L108 from Kinguélé to Tchimbélé , 0°29'N 10°17'E, 327 m, 24.X.2011, fl. bud, Maas et al. 9964 ( LBV, WAG) ; side road at km 46 of road from Kougouleu to Méla, 0°33'N 10°15'E, 21.XI.2011, fr., Maas et al. 10415 ( LBV; WAG) ; Monts de Cristal , bords de la route de Kinguélé Aval, 0°25'N 10°15'E, 34 m, 26.XI.2020, st., MBG Transect 6360 ( BRLU) .

Figures

Fig. 6. – Distribution map of Hunteria maasiorum Jongkind & E. Bidault (open circle) and Pleiocarpa robusta O. Lachenaud (closed circles). The open circle includes all cited collections of H. maasiorum.