Background and aims – This paper describes and illustrates a new species of Nectaropetalum (Erythroxylaceae) from the Sanaga River basin in Cameroon. The genus otherwise includes eight species: two in the Democratic Republic of the Congo, five in coastal areas of eastern and southern Africa, and one in Madagascar.

Material and methods – The description of the new species is based on the study of 13 gatherings, field observations, and a comparison with available material of its congeners in BR and K. Its conservation status was assessed following the IUCN Red List Categories and Criteria.

Key results – The discovery is an important westwards range extension for the genus. Nectaropetalum camerunense sp. nov. most closely resembles N. acuminatum from Tanzania in vegetative characters, but differs by its shorter sepals and short thickened pedicels (vs sessile flowers). A key to the genus Nectaropetalum is presented. The new species is endemic to the middle Sanaga basin in Cameroon, where it occurs gregariously in periodically flooded riverine forests. It is assessed as Endangered following IUCN Red List Categories and Criteria. This brings the total number of Sanaga basin riverine endemics to date to nine, all of which are currently facing significant threats from agriculture and the construction of hydroelectric dams.

Central Africa, conservation, IUCN Red List assessment, riverine forests, taxonomy, threatened species

Cameroon’s forests are among the most biologically diverse in tropical Africa (Sosef et al. 2017). Since the 1990s, important botanical inventories have been conducted in the country, resulting in the publication of several conservation checklists (Cable and Cheek 1998; Cheek et al. 2000, 2004, 2010; Harvey et al. 2004; Onana and Cheek 2011; Onana et al. 2011). These inventories have led to the discovery of numerous new species in various families, including Annonaceae (Ghogue et al. 2017; Couvreur et al. 2022), Arecaceae (Mogue Kamga et al. 2018), Balsaminaceae (Janssens et al. 2015), Fabaceae (Sonké et al. 2024), Putranjivaceae (Quintanar et al. 2023), Orchidaceae (Droissart et al. 2009; Verlynde et al. 2013; Azandi et al. 2016), Sapotaceae (Nzoyeuem Djonko et al. 2025), and Rubiaceae (Taedoumg et al. 2017; Zemagho et al. 2017, 2018; Cheek et al. 2018; Lachenaud 2019; Lachenaud et al. 2020; Álvarez-Aguirre et al. 2021; Cheek and Sonké 2025). Further discoveries are undoubtedly forthcoming, which highlights the importance of conducting additional inventories in Cameroon, and more broadly, across Central Africa. Many of these taxonomic novelties are apparently endemic to the country and are currently facing threats from human activities, such as agriculture, logging, mining, and the construction of hydroelectric dams.

In 2021, a team of scientists from Institut de Recherche pour le Développement (IRD, France), the Plant Systematics and Ecology Laboratory (University of Yaoundé I), Biotope (an environmental consultancy based in France), and the Missouri Botanical Garden initiated an Environmental and Social Impact Assessment (ESIA) for a hydro-electric project at Kikot, along the Sanaga River. This study identified several taxonomic novelties, including the recently described Drypetes stevartii Sonké & Quintanar (Putranjivaceae; Quintanar et al. 2023), Talbotiella couteronii Sonké, M.Simo & Burgt (Fabaceae; Sonké et al. 2024), Synsepalum longiflorum Nzoyeuem, O.Lachenaud & Sonké (Sapotaceae; Nzoyeuem Djonko et al. 2025), Phragmanthera bidaultii Libalah & O.Lachenaud (Loranthaceae; Simo-Droissart et al. 2026), Tristicha spinulosa E.Bidault & Rutish. (Podostemaceae; Bidault et al. 2026), as well as a new species of Nectaropetalum Engl. (Erythroxylaceae), the focus of this article.

Erythroxylaceae are a pantropical family, comprising ca 270 species in four genera (Bittrich 2014; POWO 2026) that are easily distinguishable by the characters summarised in Table 1. Most species in this family belong to the highly diverse genus Erythroxylum P.Browne. Aneulophus Benth. and Pinacopodium Exell & Mendonça are both restricted to Central Africa and currently include two species each but are probably monospecific. The last genus, Nectaropetalum, so far consists of eight species. Five of these occur in the coastal areas of eastern and southern Africa (Verdcourt 1984), two in the Democratic Republic of the Congo (Bamps 1977), and one in Madagascar (Bardot-Vaucoulon 2001).

Nectaropetalum was originally classified in Linaceae (Engler 1902) but was soon transferred to Erythroxylaceae (Stapf 1909; Stapf and Boodle 1909), a position that was subsequently accepted by most authors (e.g. Marloth 1925; Gilbert 1958; Robson 1963; Verdcourt 1981, 1984), although some placed it, along with Pinacopodium, in a separate family Nectaropetalaceae (Exell and Mendonça 1951; Badré 1973). Phylogenetic studies strongly support the inclusion of Nectaropetalaceae within Erythroxylaceae, with Aneulophus being the sister lineage to the rest of the family (Schwarzbach and Ricklefs 2000; Sun et al. 2016). Schwarzbach and Ricklefs (2000) found Nectaropetalum and Pinacopodium as forming a clade sister to Erythroxylum, while Sun et al. (2016) found Nectaropetalum as sister to Erythroxylum (they did not include Pinacopodium in their study). As both studies included only one Nectaropetalum species, N. kaessneri Engl. and N. zuluense (Schönland) Corbishley respectively, the monophyly of the genus remains to be confirmed, particularly with regards to Pinacopodium. Although the latter genus’ cymose inflorescence is unique in the family, it is otherwise extremely similar to Nectaropetalum (where its type species was originally placed) in flower and leaf characters (Table 1). It seems quite plausible, therefore, that the two genera will have to be combined, with Nectaropetalum being the older name.

Apart from the relatively frequent East African N. kaessneri, most Nectaropetalum species are uncommon and rarely collected. None has yet been recorded from the Atlantic side of the African continent (e.g. Keay 1958; Badré 1972, 1973; Sosef et al. 2006; Onana 2011), so the discovery of the genus in Cameroon represents a significant expansion of its range to the west. The geographical gap between the Cameroonian species and its relatives will be partly bridged if Pinacopodium, which is found along the Atlantic coast from Gabon to Angola (Cabinda), proves to be congeneric. While the Cameroonian plant shows all the diagnostic characters of Nectaropetalum (Table 1), it differs from all its congeners and is therefore described here as a new species. We also present the first comprehensive key to the genus.

The description of the new species, as well as information about its distribution, habitat, and phenology, is based on field work conducted in Cameroon and on the study of 13 herbarium gatherings (including spirit material), all of which were made by the authors and deposited in the following herbaria: BR, BRLU, K, M, MA, MO, P, WAG, and YA (herbarium codes according to Thiers 2026). Specimens of other Nectaropetalum species from BR and K were also studied for comparison. The descriptive terminology follows that used by Verdcourt (1984). The distribution map was made using QGIS v.3.40 (QGIS Development Team 2025) with the coordinate system set to WGS84/Pseudo-Mercator. Chorology follows White (1979). An assessment of the conservation status was made following the IUCN Red List Categories and Criteria (IUCN 2012; IUCN Standards and Petitions Committee 2024). The Extent of Occurrence (EOO) and Area of Occupancy (AOO) were calculated with GeoCAT (Bachman et al. 2011), using a 2 × 2 km grid.

Remarkably, this locally gregarious species has apparently never been collected before 2023, with no historical specimens found in herbaria to date. This is probably due to its restricted range and habitat. Indeed, riparian forests along the Sanaga were rarely explored by botanists until recently. As discussed in the introduction, several new species were discovered during the botanical inventories carried out for the environmental impact study of the Kikot hydroelectric dam project. Furthermore, Nectaropetalum camerunense, like Talbotiella couteronii which grows in the same habitat and flowers at the same time (Sonké et al. 2024), has a very short flowering period, and can easily remain unnoticed when it is not in flower.

The discovery of N. camerunense adds another species to the list of Sanaga Basin riverine endemics, which already includes Eugenia ancorifera Amshoff (Myrtaceae), Hibiscus elongatifolius Hochr. (Malvaceae), Maranthes sanagensis F.White (Chrysobalanaceae), Ostryocarpus zenkerianus Dunn (Fabaceae), Talbotiella couteronii (Fabaceae), Synsepalum longiflorum (Sapotaceae), Phragmanthera bidaultii (Loranthaceae), and Tristicha spinulosa (Podostemaceae). A new species of Turraea L. (Meliaceae), which is endemic to this area, is currently being described, and it is highly likely that more new species are awaiting to be discovered. Given the ongoing threats to their habitat, particularly from hydroelectric dams (three of which are already operating on the Sanaga, with another one under construction, and a further project at Kikot), there is an urgent need for further exploration and conservation measures.

We thank the herbarium staff of BR, BRLU, K, P, and YA for their assistance while working in their institutes. Thanks are due to Dr Martin Cheek (Royal Botanic Gardens, Kew) for his assistance to the first author. Special thanks are due to Dr Jeannette Mapi-Sonké for various support and advice to the first and second authors. Field work by BS, MS-D, and FN was undertaken as part of an environmental impact assessment for the Kikot hydro-electric dam project. Kikot Hydro-Power Company and Electricité de France (namely Charles Bodel, Frederick Jacob, and Antoinette Kiboum) are warmly thanked for their support to our taxonomical studies, including in the field. We thank Dr Tariq Stévart (Missouri Botanical Garden), Dr Nicolas Granier and Xavier Rufray (Biotope) for their support. Numerous site visits to monitor phenology of the novelty have been funded by IRD through the International Joint Laboratory DYCOFAC project. We would also like to thank Désiré Ntamack for his help during field work and all other collectors of specimens of the new species.