Introduction

The Benna Plateau, or Benna Gadyah in the Susu language, is a sandstone plateau up to 1190 m high in the Forécariah and Kindia Prefectures in Guinea, West Africa. The plateau rises high above the villages of Dalonia and Gombokori, which are at 120 m altitude. The name Benna does not appear on any maps, and the exact location is therefore not well known except to villagers living on and around the plateau. The plateau was visited by several plant collectors in the 20^th century, as demonstrated from specimens in GBIF (2021) and Kew's herbarium specimen database. The French naturalist Henri Jacques-Félix collected there several times in 1937 and returned in 1956. A number of plant taxa were described from collections made on the Benna Plateau; five of these were named after the plateau: Bafodeya benna (Scott Elliot) Prance ex F. White, Ctenium bennae Xanthos, Heterosa-mara bennae (Jacq.-Fél.) Paiva, Impatiens bennae Jacq.-Fél., and Mesanthemum bennae Jacq.-Fél.

The BR, L and P herbaria do not hold any specimens collected in the past 60 years on the Benna Plateau (GBIF 2021), and staff of the National Herbarium of Guinea are not aware of any recent collecting expeditions, which suggests that the area may not have been visited by plant collectors in the past 60 years. When the first two authors prepared an expedition to the area, in February 2019, a rocky area with vertical cliffs and canyons was observed on Google Earth (2019). In these canyons, a plant species with large leaves, belonging to the Melastomataceae, was found occurring in shade on vertical rock. These plants did not resemble any species and genus known to the collectors, who have collected many plants in West and Central Africa. It was therefore immediately understood that the plants might represent an undescribed genus and species. Plants with leaves and flower buds were collected. On the next expedition, in October–November 2019, two collections with leaves, old fruits and seeds were collected in two canyons 4.3 km apart.

We studied the three Melastomataceae specimens from the Benna Plateau by morphological and molecular analyses. Our studies confirmed that the species is new and cannot be placed in any existing genus of Melastomataceae. We present a phylogenetic tree showing the position of the new genus compared to related genera, and determine in which tribe the new genus should be placed. The morphology of the new genus is compared with that of related genera. We provide a description of the new species, an illustration, photographs and a distribution map.

Material and methods

Expeditions to the Benna Plateau were planned using Google Earth (2019) imagery. Herbarium collections were immediately dried overnight on a portable gas dryer. Photographs of plants were taken with an Olympus Tough TG5. Research permits were obtained in advance of the expeditions, and export permits for the herbarium and seed collections were obtained before their export (see Acknowledgements). The three herbarium collections were morphologically compared with herbarium collections of Melastomataceae genera found at K and images of specimens on GBIF (2021). All herbarium specimens cited have been studied by the authors. Flower buds from one of the three collections were dissected and observed with a light microscope. Plant terminology follows Beentje (2016). The distribution map was prepared with Geocat (2021). An IUCN Red List assessment was made according to the methodology in IUCN (2012, 2019).

Phylogenetic inference — A total of 245 accessions representing all currently accepted Melastomataceae tribes were sampled for the phylogenetic placement of the theorized new species and genus. All African (including Madagascan) endemic genera (including type species) currently placed in the Sonerileae were sampled: Amphiblemma Naudin 12 of all 15 species were sampled, Calvoa Hook. f. 8/19, Cincinnobotrys Gilg 4/8, Dicellandra Hook. f. 2/3, Gravesia Naudin 25/116 and Preussiella Gilg 1/2. Seventeen Medinilla Gaudich. species, from mainland Africa (1), Madagascar (4) and Asia (12), were also sampled. Feliciadamia Bullock could not be sampled; the genus was placed in Feliciadamieae by Jacques-Félix (1994). A total of 46 species of Asian Sonerileae and a single species of each of three American Sonerileae genera, Boyania Wurdack, Phainantha Gleason and Tryssophyton Wurdack, were also sampled. As outgroup, 105 species representing the remaining currently accepted Melastomataceae tribes were included.

Total genomic DNAs were extracted, amplified and sequenced as described in Veranso-Libalah & al. (2017, 2018, 2020). We amplified and sequenced two nuclear loci (the nuclear ribosomal internal transcribed spacer (nrITS) and the nuclear ribosomal external transcribed spacer (nrETS)) and three plastid loci (accD-psaI, psbK-psbL and ndhF), which have been widely used in phylogenetic studies across the Melastomataceae (Michelangeli & al. 2004, 2008, 2011, 2013; Kriebel & al. 2015; Reginato & Michelangeli 2016; Rocha & al. 2016; Veranso-Libalah & al. 2017, 2018, 2020; Guimarães & al. 2019; Kartonegoro & al. 2021). Additional sequences were obtained from GenBank.

Using SEQUENCHER v.4.1.4 (Gene Codes Corporation, Ann Arbor, MI, U.S.A.), contigs of forward and reverse sequences were assembled and manually edited. Sequences were aligned using MAFFT v.7 (Katoh & Standley 2013) and then manually adjusted in MESQUITE v.3.10 (Maddison & Maddison 2016). The best-fit substitution model for each aligned locus was determined using the Akaike information criterion (AIC) in JMODELTEST 2.1.4 (Darriba & al. 2012). The GTR+ G model was suggested as the most appropriate nucleotide substitution models for nuclear and plastid datasets.

Maximum likelihood (ML) and Bayesian inference (BI) analyses were performed using the CIPRES Science Gateway v.3.3 ( https://www.phylo.org/, Miller & al. 2010). Phylogenetic analyses were initially conducted on the plastid (ndhF, psbK-psbL and accD-psaI) and nuclear (nrETS and nrITS) datasets using the ML and BI methods. Gene trees from the plastid and nuclear datasets revealed no well-supported topological conflicts. As such, all further analyses were performed using the concatenated 5-loci data set (ndhF, psbK-psbL, accD-psaI, nrETS and nrITS). Maximum likelihood analyses were performed using RAxML v.8 (Stamatakis 2014) with a GTRGAMMA model of sequence evolution. The ML analyses were conducted using default parameters in RAxML (Stamatakis 2014) with 1000 bootstrap replicates (Felsenstein 1985).

The BI analyses were performed using BEAST v.2.5.0 (Bouckaert & al. 2019). Four independent Markov chain Monte Carlo (MCMC) analyses were run, each of 30 million generations sampling every 3000 generations. All xml files were prepared using BEAUTI and ran on the CIPRES Science Gateway v.3.3 ( https://www.phylo.org/, Miller & al. 2010). We used TRACER v.1.6 (Rambaut & Drummond 2013) to assess convergence and effective sampling size (ESS) of all parameters from the output log files. As burn-in, 25% of samples were removed prior to combining the independent runs using LOGCOMBINER v.2.5. (Bouckaert & al. 2019). A maximum clade credibility tree was constructed using TREEANNOTATOR v.2.5. (Bouckaert & al. 2019) and node support was expressed as posterior probability (PP).

Results

Phylogenetic placement — Molecular sequence data obtained from two of the three collections, Burgt & al. 2274 and 2323, suggests they are nested within the tribe Sonerileae (Fig. 1). The two collections are unrelated to the other African (including Madagascan) Sonerileae genera (Fig. 1), all of which were sampled in the present study. They are weakly supported (BS 57%) as sister to the South American genus Phainantha. Of the six currently accepted American Sonerileae genera, only three genera were sampled in the present study.

Fig. 1.

Phylogeny showing the position of Benna alternifolia within the tribe Sonerileae.

Fig. 2.

Benna alternifolia – A: branch showing alternate leaf arrangement, with two inflorescences and seven leaves: five mature leaves of which three removed, a young leaf, and a very young leaf; B: flower bud; C: petal inner surface; D: flower bud in longitudinal section with petals partly removed; E: large stamen back and front, small stamen back and front; F: ovary of flower bud in transverse section; G: ovary of flower bud seen from above; H: old infructescence with fruits partly decomposed; J: fruit; K: seeds. – Origin: A from Burgt & al. 2274 (type gathering) and Burgt & al. 2323; B–G from Burgt & al. 2274; H–K from Burgt & Haba 2333. – Drawing by Xander van der Burgt.

Fig. 3.

Benna alternifolia – A: the largest population was found in a deep canyon, of which the upper part is visible at the centre of the photograph, on a 1040 m-high hill on the Benna Plateau; B: plants in their habitat, on vertical rock in deep shade, under overhanging rocks, out of reach of falling rain drops, but within reach of permanently seeping water; C: group of four plants; D: single plant. – Origin: A, C from Burgt & al. 2274 (type gathering); B from Burgt & al. 2323; D from Burgt & Haba 2333. – All photographs by Xander van der Burgt.

Morphology — The three collections from the Benna Plateau, Burgt & al. 2274, 2323 and Burgt & Haba 2333, clearly belong in Melastomataceae, shown by the leaf blade with 11–15 veins all starting from the top of the petiole (Fig. 2, 3, 4), as well as by the characters of the flower buds and fruits, which match the family description given by Utteridge & Bramley (2015). On morphological grounds, the three collections are placed in the Sonerileae; all other Melastomataceae tribes can be ruled out. For example, the three collections are not in the Melastomateae (the most diverse tribe in Africa) because the seeds are not cochleate. Most Sonerileae are herbaceous plants of shady habitats, with capsular, apically dehiscent fruits (Renner 1993), as are the plants from which the three collections were made (Fig. 2, 3). Morphologically, the three collections are different from all African (including Madagascan) Melastomataceae species, including all species in the seven currently accepted African Sonerileae genera. A morphological comparison between the three collections and these seven genera is presented in Table 1. The three collections also do not match any of the currently accepted American and Asian Melastomataceae genera. Leaves such as those of the three collections occur in a number of species outside of Africa, for example in Ochthephilus re-pentinus Wurdack (Merianieae), Quipuanthus epipetricus Michelang. & C. Ulloa (Cyphostyleae) and Tigridiopalma magnifica C. Chen (Sonerileae), but the structure of the inflorescences and flowers of these species is very different.

A morphological comparison between all six American Sonerileae genera and the three collections from the Benna Plateau is presented in Table 2. African Sonerileae usually have 4- or 5-merous flowers with a 4- or 5-locu-lar ovary (Table 1), but American species are typically anisomerous, having a 4-, 5- or 6-merous flowers with a 3-, 4- or 5-locular ovary with exceptions in Tateanthus Gleason and Phainantha (Table 2). We conclude from both morphological and molecular analysis that the three collections from the Benna Plateau, Burgt & al. 2274, 2323 and Burgt & Haba 2333, represent a new, monotypic genus. The genus is named Benna Burgt & Ver.-Lib. and the species is named Benna alternifolia Burgt & Ver.-Lib. in the taxonomy section of the present manuscript.

Fig. 4.

Benna alternifolia – A: leaf upper surface; B: leaf lower surface; C: inflorescence with flower buds; D: roots. – Origin: A, D from Burgt & Haba 2333; B, C from Burgt & al. 2274 (type gathering). – All photographs by Xander van der Burgt.

Discussion

Melastomataceae are a pantropical family, with c. 160 genera, c. 5000 species and tropical centres of diversity in South America and SE Asia (Utteridge & Bramley 2015). Guinea has c. 63 Melastomataceae species in 27 genera, counted from specimens in GBIF (2021) and Kew's herbarium specimen database. Four genera are endemic or near-endemic to Guinea, as well as monospecific. The three endemic species are Benna alternifolia, Cailliella praerupticola Jacq.-Fél. and Feliciadamia stenocarpa (Jacq.-Fél.) Bullock (Lisowski 2009), while the near-endemic Anaheterotis pobeguinii (Hutch. & Dalziel) Ver.-Lib. & G. Kadereit (Veranso-Libalah & al. 2017) occurs also in Sierra Leone.

Sonerileae are a very diverse tribe that occurs in SE Asia (c. 800 species in 31 genera), Madagascar (184/2), Africa (excluding Madagascar, 55/7) and America (12/6) (Michelangeli & al. 2020). It is remarkable that the closest relatives of the genus Benna occur in tropical America, because the Sonerileae diversity is much lower than in tropical Africa and Asia. There are other examples of African plants having South American affinities. Guinea, one of the African countries situated closest to the American continent, has several remarkable examples. In Guinea occur two near-endemic American families with a single species that is native outside America: Bromeliaceae, represented in Africa by the Guinea endemic species Pitcairnia feliciana (A. Chev.) Harms & Mildbr., and Rapateaceae, represented in Africa by the West African endemic species Maschalocephalus dinklagei Gilg & K. Schum. occurring from Guinea to Ivory Coast. These two species originated by long-distance seed dispersal from the American continent (Givnish & al. 2004; Renner 2004), as was hypothesized by Hepper (1965), Thorne (1973) and Brenan (1978). Another example of a Guinean plant species with South American affinities is Calophyllum africanum Cheek & Q. Luke (Clusiaceae). This species was described as endemic to Mali (Cheek & Luke 2016) but has been collected in 2019 on the Benna Plateau and several other places in Guinea by the first two authors of the present study. The hypothesis is here proposed that the presence of B. alternifolia in Guinea is the result of a long-distance seed dispersal event from the American continent. This dispersal route is also similar for the tribe Melastomateae (Veranso-Libalah & al. 2018).

Melastomataceae species generally have an opposite leaf arrangement. Anisophylly occurs commonly, especially in Sonerileae, for example in Amphiblemma (Jacques-Félix 1974a) and Cincinnobotrys (Jacques-Félix 1976). The existing three collections of Benna alternifolia show no signs of anisophylly at all, and therefore the hypothesis is proposed here that the leaves are alternate. Future studies of living plants and of additional, new collections might confirm this hypothesis or determine that the leaf arrangement of Benna is an extreme example of anisophylly.

An alternate leaf arrangement, such as in Benna alternifolia (Fig 2A), is uncommon among Melastomataceae. A search for Melastomataceae species on IPNI (2021) and POWO (2021) with the species name alternifolia, alternifolium or alternilamina, resulted in five accepted species, from four different genera and tribes: Bertolonia alternifolia Baumgratz, Amorim & A. B. Jardim (Bertolonieae), Blakea alternifolia Gleason (Blakeeae), Heteroblemma alternifolium (Blume) Cámara-Leret, Ridd.-Num. & Veldkamp (Sonerileae), Miconia alternifolia (Griseb.) Alain and Miconia alternilamina Michelang. (Miconieae). The tendency toward an alternate leaf arrangement seems to have originated independently among these lineages; as such, the alternate leaf arrangement of Benna alternifolia does not indicate in which tribe the species may be placed. There are more species with a tendency toward an alternate leaf arrangement among the c. 5000 Melastomataceae species. Medinilla mirabile (Gilg) Jacq.-Fél. may have alternate leaves on the lower part of the stem, while the leaves are verticillate on the upper stem (Hutchinson & Dalziel 1954, Jacques-Félix 1983). The species of Cincinnobotrys are small herbs with short stems and internodes. The degradation of one of the two leaves of a pair (Jacques-Félix 1976) gives the appearance of an alternate leaf arrangement. Species in the genus Phainantha, the hypothesized sister-group of Benna, may have opposite leaves, but the leaves more frequently appear alternate through abortion of one of the leaves of a pair (Ulloa Ulloa & Neill 2006). In Phainantha, all leaves on one side of the stem are replaced by climbing roots (Renner 1993: 527).

The alternate branching of the inflorescence in Benna alternifolia is not common among African Melastomataceae; however, in Amphiblemma molle Hook. f., the inflorescence is a uniparous cyme bearing alternate, subsessile flowers (Jacques-Félix 1974a). Among the African Melastomataceae, scorpioid cymes are very common as well as restricted to Sonerileae; but the inflorescence of B. alternifolia is not scorpioid. Sonerileae more rarely have paniculate cymes (Renner 1993: 532), as in B. alternifolia.

Taxonomy

Benna Burgt & Ver.-Lib., gen. nov.

Type: Benna alternifolia Burgt & Ver.-Lib.

Diagnosis — The genus Benna differs from all other African Melastomataceae genera by the following combination of characters: Herbs. Leaves alternate, venation acrodromous, margin dentate. Inflorescence cymose, paniculate, axillary, branching alternate. Flowers actinomorphic, epigynous, 4-merous, 8 dimorphic stamens. Fruit a capsule, apically dehiscent, containing many seeds. Seeds obovoid or nearly so, glossy, testa smooth. The genus Benna is placed in the tribe Sonerileae. A morphological comparison between Benna and the seven currently accepted African Sonerileae genera is presented in Table 1. A morphological comparison between Benna and the six currently accepted American Sonerileae genera is presented in Table 2.

Benna alternifolia Burgt & Ver.-Lib., sp. nov. – Fig. 2, 3, 4.

Holotype: Guinea, Forécariah Prefecture, slopes of Benna Plateau, 3 km W of Gombokori village, 09°44′06″N, 12°49′00″W, 770 m, flower buds, 11 Feb 2019, Burgt, Haba, Konomou & Xanthos 2274 (HNG; isotypes: K001381567, MO, P, WAG).

Description — Herbs, perennial, evergreen, half-spherical in shape, up to 1.2 m in diam., with up to 60 leaves per plant. Roots woody; thin roots up to 0.5 m × 4 mm, radiating on rock surface and attaching plant to rock; thick roots up to 10 m × 2 cm, entering rock fissures in search of permanent water seepage, bark deeply fissured, up to 5 mm thick. Stems somewhat woody, branched from base, pendent, circular in cross-section, up to 28 cm × 6–12 mm, reddish green, densely to sparsely hairy with red hairs up to 4 mm long, puberulent with red glandular hairs up to 0.1 mm long; internodes up to 3 cm long, leaf petiole pointing in same direction as internode just below it. Leaves alternate; petiole succulent, 15–45 cm × up to 6 mm, reddish green to bright red, densely hairy to glabrescent with red hairs up to 7 mm long, puberulent with red glandular hairs up to 0.1 mm long; leaf blade round to ovate, 12–31 × 10–28 cm, shrinking a little during drying, lower surface dull glaucous light green, upper surface glossy green, both surfaces puberulent with red glandular hairs up to 0.1 mm long, veins below with red hairs up to 5 mm long; leaf base deeply cordate, left or right half of leaf base often overlapping other half; leaf margin dentate, teeth with a single red hair up to 4 mm long, distance between teeth 4–24 mm; leaf apex rounded, mucronate; leaf venation acrodromous, 11–15 veins all starting from top of petiole, central vein straight, other veins curved, otherwise similar in appearance to primary vein, secondary and tertiary venation scalariform, venation on lower surface prominent, light red, on upper surface flattened, light red. Inflorescence cymose, paniculate, axillary, up to 4 cm long when in bud, with up to c. 70 flower buds, branching alternate; peduncle up to 1 × 3 mm, internodes 0.5–15 mm long; bracts and bracteole persistent, lanceolate, c. 1 mm long; peduncle and rachides red, puberulent with red glandular hairs up to 0.1 mm long. Flowers: flower buds 4-mer-ous, epigynous; pedicel up to 24 mm long, red, puberulent with red glandular hairs up to 0.1 mm long; hypanthium cupuliform, c. 4 × 4 mm, light reddish green, puberulent with red glandular hairs up to 0.1 mm long, part of hypanthium free from ovary c. 2 mm long; calyx lobes 4, free, triangular, c. 1.5 × 2.5 mm, light green with pink apex, puberulent with red glandular hairs up to 0.2 mm long, margin ciliate, apex mucronate, mucro c. 0.3 mm long; petals 4, free, convolute, overlapping counterclockwise when viewed from above, alternate to sepals, round to ovate, in bud c. 6 × 5 mm, light pink, both surfaces and margin glabrous, acuminate with acumen c. 1 mm long, claw c. 0.5 × 1 mm; stamens 8, fertile, actinomorphic, dimorphic, glabrous; 4 antisepalous stamens: filaments c. 2 mm long, connective with a 3-lobed appendage, c. 2 × 2 mm, anther c. 3 × 1 mm, with 2 loculi; 4 antipetalous stamens: filaments c. 1 mm long, connective with a 3-lobed appendage, c. 1 × 1 mm, anther c. 2 × 1 mm, with 2 loculi; ovary inferior, in bud c. 2 mm long, 4-locular, loculi opposite sepals, each locule with c. 100 ovules; style straight, in bud c. 4 mm long, glabrous, stigma punctiform. Infructes-cence up to 9 cm long, with up to 70 fruits, peduncle up to 1 × 4 mm, internodes 0.5–18 mm long, lower internodes up to 2 mm long, middle internodes up to 18 mm long, upper internodes up to 5 mm long; bracts and bracteole caducous; peduncle and rachides red, puberulent with red glandular hairs up to 0.1 mm long. Fruit a capsule, urceolate, 4–5 × 3–4 mm, glabrescent, calyx persistent, fruit apically dehiscent, crown lobes not seen; fruit pedicel 20–60 mm long. Seeds up to 400 per fruit, obovoid or nearly so, 0.4–0.5 × 0.3–0.4 mm, glossy, testa smooth, yellow to light brown.

Table 1.

Morphological comparisons of the new genus Benna with all seven Sonerileae genera occurring in Africa (including Madagascar): Amphiblemma (Jacques-Félix 1974a), Calvoa (Figueiredo 2001), Cincinnobotrys (Jacques-Félix 1976), Dicellandra (Jacques-Félix 1974b), Gravesia (Naudin 1851), Medinilla (Gaudichaud-Beaupré 1829–1830) and Preussiella (Jacques-Félix 1977). The dash (–) indicates unknown data.

Table 2.

Morphological comparisons of the new genus Benna with all six Sonerileae genera occurring in tropical America: Boyania (Maguire & Wurdack 1964), Neblinanthera Wurdack (Maguire & Wurdack 1964), Opisthocentra Hook. f. (Bentham & Hooker 1867), Phainantha (Ulloa Ulloa & Neill 2006), Tateanthus (Gleason 1931) and Tryssophyton (Maguire & Wurdack 1964; Wurdack & Michelangeli 2019). The dash (–) indicates unknown data.

Phenology — Benna alternifolia flowers in February–March and fruits a few months later. Old, decaying fruits containing ripe seeds may remain on the plants until November, because the plants are little disturbed by wind and rain in their sheltered habitat.

Distribution — Benna alternifolia is endemic to Guinea (Fig. 5) and occurs in Forécariah Prefecture near border with Kindia Prefecture, in canyons of the Benna Plateau near villages Dalonia and Gombokori.

Fig. 5.

Distribution of Benna alternifolia, blue dots. Map data © Google 2021.

Habitat and ecology — Benna alternifolia occurs on vertical sandstone rock, in deep shade in canyons 10–100 m deep (Fig. 3), and on vertical sandstone rock in deep shade of trees, at 300–800 m altitude. Plants occur only under overhanging rocks (Fig 3B), out of reach of falling rain drops, and only on vertical rock where water is seeping all year round, within reach of the several-meter-long roots. In this habitat, the perennial, evergreen, herbaceous plants, which do not have a rootstock, can continue to grow during the six-month dry season.

Benna alternifolia is often found together with Cincinnobotrys felicis (A. Chev.) Jacq.-Fél. (Melastomataceae), Impatiens bennae (Balsaminaceae) and Mesanthemum bennae (Eriocaulaceae). On the same vertical rocks, but higher up and in sunny, seasonally dry habitat, two plant species endemic to Guinea occur abundantly: Cailliella praerupticola (Melastomataceae) and Pitcairnia feliciana (Bromeliaceae), the only member of the family that is native outside America.

Conservation status — Benna alternifolia is currently known only in the Benna Plateau in Forécariah Prefecture. The collectors searched for the species elsewhere in the region, without success. The habitat of the species was found to occur widespread in an expanse of sandstone plateaus occupying much of Coyah, Dubreka, Forécariah and Kindia Prefectures in Guinea (Fig. 5), but the species was not found. The Benna Plateau is currently unprotected and was not proposed as a TIPA (Tropical Important Plant Area) by Couch & al. (2019), because the exact location of the Benna Plateau was unknown to the authors at the time of that publication. The Benna Plateau is rich in rare plant species and is proposed here to become a TIPA.

The extent of occurrence of Benna alternifolia was 3.4 km² and the area of occupancy was 12 km², both calculated with Geocat (2021). The extent of occurrence is changed to 12 km², because it should not be smaller than the area of occupancy (IUCN 2019). The number of locations is two. These values may become larger if the species is found in other canyons. The species currently does not seem exposed to any threats. The habitat where the species occurs is free of fire. There are no known mineral deposits in the vicinity. Plants were only found in remote canyons where they will not be threatened by rock quarrying. In absence of any threats to the species, IUCN (2012) categories A, B and C are not eligible. About 680 mature individuals of B. alternifolia were found. There exist probably more than 1000 mature individuals, because some canyons in and near the Benna Plateau are yet to be explored. The species may be close to qualifying for the IUCN (2012) Red List category Vulnerable under criterion D1, which has a threshold of 1000 mature individuals, and B. alternifolia is therefore assessed here in the IUCN category Near Threatened.

Seed conservation — Seeds were collected from 12 plants of Burgt & Haba 2333 and are stored in the seed bank of the National Herbarium of Guinea in Conakry (c. 250 seeds) and at Kew's Millennium Seed Bank (also c. 250 seeds).

Etymology — The genus is named for the Benna Plateau or Benna Gadyah in the Susu language. The Benna Plateau holds the only known locations for the species. The specific epithet refers to the alternate leaf arrangement.

Vernacular name — In the Susu language, the name of Benna alternifolia is Labalaba Khamè or Labalaba Hamey, which means “male soft leaf”. The name Labalaba is given to Piper umbellatum L. (Burkill 1997, vol 4: p. 441), a herb with leaves similar in size and appearance. On the Benna Plateau, Piper umbellatum is named Labalaba Guinè, which means “female soft leaf”.

Additional specimens examined — GUINEA: Forécariah Prefecture, canyon at base of Benna Plateau, 3.5 km N of Dalonia village, 09°41′53″N, 12°50′03″W, 330 m, fruits, 26 Oct 2019, Burgt, Haba & Holt 2323 (B, HNG, K, MO, P, WAG); slopes of Benna Plateau, 3.5 km W of Gombokori village, 09°44′07″N, 12°49′26″W, 810 m, fruits, 1 Nov 2019, Burgt & Haba 2333 (HNG, K).

Author contributions

SM hosted the research and arranged the research and plant export permits. XvdB planned the plant collecting expeditions. XvdB and PMH led the plant collecting expeditions. XvdB performed the morphological analysis and wrote the description. MCVL performed the molecular analysis and verified the morphological analysis. All authors commented on the manuscript and approved the final version.