Uvariopsis niangadoumae Couvreur & Dagallier, 2025

Couvreur, Thomas L. P., Niangadouma, Raoul, Nguimbit, Igor, Paradis, Anne-Hélène, Dagallier, Léo-Paul M. J., Baudoin-Huit, Lola, Collin, Myriam, Haran, Julien M. & Droissart, Vincent, 2025, Passion and combat on a floral stage: a new species of Uvariopsis (Annonaceae) from Monts de Cristal, Gabon, with notes on its unique pollination ecology, Plant Ecology and Evolution 158 (2), pp. 294-308 : 294-308

Uvariopsis niangadoumae Couvreur & Dagallier sp. nov.

Figs 1 , 2 , 3

Type

GABON – Estuaire • Monts de Cristal National Park, ca 6 km before Kinguélé, in forest located ca 500 m after concrete sign indicating the entrance to the park towards Kinguélé, then 500 m along the Sobéa river after passing clearing for high tension cables on the west of the road ; 00°25.297’N, 10°15.447’E; 90 m; 12 Nov. 2023; fl., fr.; Couvreur T. L. P. & Niangadouma R. 1803; holotype: WAG!; isotypes: LBV!, MPU!, P !.

Diagnosis

Uvariopsis niangadoumae resembles U. korupensis in the shape and dimensions of its leaves and the overall size of the flowers. It differs by having strong scented leaves versus no clear scent in U. korupensis . Furthermore, U. niangadoumae bears no more than two, few-flowered inflorescences on small protrusions at the base of the trunk, whereas in U. korupensis the base of the trunk is densely covered with inflorescences. Flowers of U. niangadoumae have free petals with a length: width ratio between 1.3 and 1.7 vs fused at base and a l: w ratio between 2.2 and 7 in U. korupensis . Uvariopsis niangadoumae also has fewer carpels than U. korupensis (20–25 vs 25–120).

Description

Tree up to 5 m tall, up to 9 cm in diameter at breast height, multi-branched, old branches grey, striate, glabrous; very young branches light green, pubescent; slash light cream with a black ring. Leaves alternate; petiole 3–4 mm long, 4 mm in diameter, glabrous, leaf blade inserted on top; lamina 33–36 cm × 9–10 cm wide, length / width ratio 3.6 to 3.8, elliptic, acuminate, acumen ca 2 cm long, base narrowly cordate, glabrous on both sides, emitting a strong scent with similarities to both mint and thyme, young laminas light green pending; secondary veins 17 to 19, brochidodromous, arching 0.5 to 1 cm from margin, tertiary veins reticulate, slightly visible above and below. Inflorescences cauliflorous at the base up to 1 m high on the main trunk, on small protuberances. Flowers functionally unisexual, monoecious, but with more female flowers than male per individual stem; flower buds conical; male and female flowers similar, but female flowers larger and more robust; female flowering pedicels up to 4 cm long, ca 4 mm in diameter, sparsely covered with hairs less than 1 mm long, one bract present at base of pedicel, 0.5 mm long and wide, soon falling; male flowering pedicel 2 cm long, 2 mm in diameter, glabrous or with sparse hairs less than 1 mm long, bracts not seen, probably soon falling. Female flowers sepals 2, ca 1 × 4 mm wide, orbicular, acuminate, glabrous, green to dark green, slightly reflexed; petals 4, in the same whorl, ca 2 × 1.5 cm wide, ca 5 mm thick, triangular, apex acute, base truncate, outer surface with raised central vein and a network of smaller veins, glabrous with ciliate margins, hairs less than 0.5 mm, pink reddish in vivo, inside surface heavily warty, glabrous, cream to pink in vivo. Floral receptacle ca 1 cm wide, slightly convex. Carpels 20 to 25, 5 mm long, 3 mm in diameter, cream, covered in hairs less than 0.5 mm long, cream; stigma sessile less than 0.5 mm long, glabrous, cream; ovules biseriate. Some female flowers with sterile stamens at the base forming 2 to 10 whorls. Male flowers sepals 2, minute, glabrous; petals 4, sometimes flowers with three petals but rare, ca 1.5 × 0.9 cm wide, ca 3 mm thick, triangular, apex acute, base truncate, free, outer and inner surfaces like female flowers, pink reddish outside in vivo, cream to pink inside in vivo. Receptacle 5 mm in diameter, strongly concave; stamens ca 400, less than 0.5 mm long, cream to light yellow in vivo. Fruiting pedicel ca 3–4 cm long, 2 mm in diameter, sparsely pubescent, green. Young monocarps light green, older monocarps darker green, monocarps 1 to 3, ca 4 cm long (3 cm when dried), 2 cm in diameter (1.5 cm when dried), surface smooth, glabrous; immature seeds biseriate, 5 per side. Hilum and raphe not seen.

Distribution

Endemic to Gabon, Monts de Cristal National Park.

Habitat and ecology

Uvariopsis niangadoumae occurs on rocky soil on a slope at the base of a hill and along a stream, leading to a larger river. To date, it is only known from a single locality. We prospected the area extensively over three visits. It appears to occur within an area of about 40 × 20 m (ca 800 m 2). We saw about 100 individuals, most of them in flower or fruit at the time of the survey. The taller individuals were generally located towards the base of the hill near the Sobéa river (an affluent of the larger Mbé river).

Phenology

Flowering in October and November. Fruits seen in November.

Etymology

This species is dedicated to the Gabonese botanist Raoul Niangadouma who participated in the (long and arduous) botanical inventories that led to the official recognition of the Monts de Cristal National Park. Raoul Niangadouma is also one of the collectors of the type specimen of this species.

Preliminary IUCN conservation assessment

Uvariopsis niangadoumae is a rare species, currently known from a single population located in the Monts de Cristal massif in Gabon, within the Monts de Cristal National Park. As such, the AOO is 4 km 2 and the EOO cannot be calculated. This unique population is threatened by the flooding expected to result from the Kinguélé Aval dam project. The population is located along a small stream adjacent to the Sobéa River, an affluent of the larger Mbé River. According to the IUCN guidelines ( IUCN 2012), the species is known from two distinct locations: one of around 60 individuals within the projected flood zone, which will be lost if the dam is built, and another of around 40 individuals at higher elevation outside the immediate flood risk area. Although the second location will not be directly submerged, it remains exposed to habitat alteration or degradation, as local environmental conditions are likely to be disrupted.

Despite extensive searches conducted during complementary inventories for the Kinguélé Aval project, no additional populations were located within the immediate project area. While the Kinguélé region represents one of the most thoroughly surveyed areas within the Monts de Cristal massif, vast portions of this massif remain unexplored. This is evidenced by the discovery of numerous species described or currently under description in recent years, such as Hunteria maasiorum Jongkind & E. Bidault , described in 2022 as part of this same project ( Jongkind and Lachenaud 2022). Only a limited stretch of the Sobéa River, where Uvariopsis niangadoumae is located, has been surveyed. Further targeted efforts should focus on exploring upstream areas of the Sobéa where habitats remain unaffected, as well as other tributaries of the Mbé River, to locate additional populations of this species.

Although there is no doubt that Uvariopsis niangadoumae is rare, similar cases of recently described species initially believed to be highly localized have demonstrated that additional populations can be discovered through targeted fieldwork. For instance, Sirdavidia solannona Couvreur & Sauquet and Trichoscypha nyangensis Pellegr. were both found in new localities after additional surveys.

In the meantime, conservation efforts for Uvariopsis niangadoumae are underway. Its population is being monitored, particularly for fruiting individuals, to support ex situ propagation efforts. The Kinguélé Aval project has also established a conservation nursery where seeds and seedlings of species of concern are maintained, currently encompassing 56 species. Twenty individuals of this new species are now growing in the nursery.

Based on current knowledge, if Uvariopsis niangadoumae were to be assessed under the IUCN Red List Categories and Criteria, it would qualify as Endangered (EN) under criterion B, due to its restriction to a single population spread across two locations and the imminent threat posed by the dam project. We recommend ongoing botanical surveys in the region to search for potential new populations of Uvariopsis niangadoumae and the continuation of ex situ conservation efforts.

Additional specimens examined

GABON – Estuaire • Parc National des Monts de Cristal, rive gauche de la Sobéa (à l’ouest de la route Kinguélé – Andok Foula ); 00°25’20”N, 10°15’25”E; 115 m; 23 Oct. 2020; fl.; Lachenaud O. et al. 3111; BRLU, LBV, MO • Parc National des Monts de Cristal, au NW de la route Kinguélé – Andok Foula, rive gauche de la Sobéa ; 00°25’13”N, 10°15’26”E; 99 m; 22 Oct. 2023; fl.; Paradis A. - H. et al. 1049; BR, BRLU, LBV, MO, P, WAG .

Figures

Figure 1. Uvariopsis niangadoumae, natural habit and vegetative characters. A. Habitat along a small stream. B. General view. C. Young leaves, light green, dropping. D. Detail of adaxial side of leaf base. E. Detail of abaxial side of leaf base. From Couvreur 1803. Photos by Thomas L. P. Couvreur.

Figure 2. Uvariopsis niangadoumae, detail of male and female flowers. A. Detail of inner side of female (left) and male (right) flowers, one petal removed. B. Detail of female flower, one petal removed. C. Detail of inner side of one female petal. D. Old female flower. E. Detail of sepals on male flower. F. Young male flower, not at anthesis yet. From Couvreur 1803. Photos by Thomas L. P. Couvreur. Scale bars: A – D = 0.5 cm.

Figure 3. Uvariopsis niangadoumae, detail of fruits and flower visitors. A. One monocarp. B. Longitudinal section of a single monocarp showing the seeds. C. Male flower with small Diptera visitors. D. Female flower with one large Staphylinidae beetle. F. Upper side of male flower covered with Crematogaster sp. ants. F. Male flower with large Staphylinidae beetle emerging covered in pollen. From Couvreur 1803. Photos by Thomas L. P. Couvreur. Scale bars: A, B = 1 cm.