A new species of Rhaptopetalum (Lecythidaceae) from south-western Gabon 39 A new species of Rhaptopetalum (Lecythidaceae) from south-western Gabon David Kenfack1,2, Diosdado Ekomo Nguema3 1 Forest Global Earth Observatory (ForestGEO), Smithsonian Tropical Research Institute, Apartado Postal 0843- 03092, Panamá, República de Panamá 2 Physical address: Department of Botany, National Museum of Natural History - MRC 166, P.O. Box 37012, Washington, DC 20013-7012, USA 3 Gabon Biodiversity Program, Centre for Conservation and Sustainability, Smithsonian Conservation Biology Institute, BP 48, Gamba, Gabon Corresponding author: David Kenfack (kenfackd@si.edu) Academic editor: Thomas L.P. Couvreur  |  Received 18 March 2019  |  Accepted 24 May 2019  |  Published 23 July 2019 Citation: Kenfack D, Nguema DE (2019) A new species of Rhaptopetalum (Lecythidaceae) from south-western Gabon. PhytoKeys 128: 39–46. https://doi.org/10.3897/phytokeys.128.34640 Abstract Rhaptopetalum rabiense Kenfack & Nguema, sp. nov. from the Rabi forest in south-western Gabon is described, illustrated and assigned a provisional conservation status of “Critically Endangered”. An iden- tification key to the five Gabonese species of Rhaptopetalum is also provided. Keywords ForestGEO, Gabon, IUCN Red List, new species, permanent plot, Rabi, rainforest, taxonomy Introduction Rhaptopetalum Oliv. is a genus of 12 species of trees, mostly confined in the Gulf of Guinea, with only one species occurring in west Africa (Cheek et al. 2002; Prance and Jongkind 2015). The genus was first described in 1865 by the English botanist Daniel Oliver (1865), as a member of the family Scytopetalaceae. Recent molecular phylo- genetic analyses (Morton et al. 1997; Mori et al. 2007) showed that Scytopetalaceae PhytoKeys 128: 39–46 (2019) doi: 10.3897/phytokeys.128.34640 http://phytokeys.pensoft.net Copyright Authors. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. RESEARCH ARTICLE Launched to accelerate biodiversity research A peer-reviewed open-access journal David Kenfack & Diosdado Ekomo Nguema / PhytoKeys 128: 39–46 (2019)40 form a monophyletic group with Lecythidaceae. Yet, opinions still diverge about either keeping the Scytopetalaceae as a separate family (Takhtajan 2009; Reveal 2011) or as a subfamily within Lecythidaceae (Mabberley 2008; APG 2016). Here, we consider Rhaptopetalum as a member of the Lecythidaceae s.l. Eight species of Rhaptopetalum are cited in the Flore du Gabon account of Scytopetalaceae (Letouzey and White 1978). However, because no specimen citation was provided for four of them (R. breteleri R. Letouzey, R. depressum R. Letouzey, R. roseum (Gürke) Engler and R. sessilifolium En- gler), their presence in Gabon remains doubtful. Hence, only four species are currently recognised in Gabon (Prance and Jongkind 2015). In 2010, we established a 25-ha permanent plot in the rainforest of south-western Gabon to study the long-term dynamics of this forest (Memiaghe et al. 2016). The methods included the challenging task of identifying to species level hundreds of thou- sands of sterile trees and saplings with diameter at breast height (dbh) ≥ 1cm. Amongst the 175,830 trees recorded in the plot, 299 were assigned to Rhaptopetalum Oliv., based on the short petiolate leaves with punctate lamina, the flowers with articulated pedicel and cupuliform calyx, the stamens attached to the base of the pseudocorolla, the poricidal anthers, the short filaments and the pubescent seeds. The identification of the Rabi material, using the key in the recent revision of the African Lecythidaceae (Prance and Jongkind 2015), was problematic from the second couplet. The species does not fit either of the leads 3 or 4, because the ovary has few (generally 1) ovules per locule, is dome-shaped, while the fruit surface is not angled. Hence, following the lead 4, the Rabi species is close to the Gabonese Rhaptopetalum belingense Letouzey with its dome-shaped ovary, its entire calyx margin, its apex placentation and smooth fruits. Following lead 3, it also resembles the Democratic Republic of the Congo R. evrardii R. Germain with its puberulous midrib, red petals and cupuliform calyx and the pedicel not articulated immediately below the calyx. However, the Rabi material also presents a suite of unique characters outlined below (Table 1) and that allows us to describe it as new to science. Table 1. Comparison of discriminant characters amongst Rhaptopetalum rabiense, R. evrardii and R. belingense. R. rabiense R. evrardii R. belingense Indumentum of young branches Puberulous Puberulous Glabrous Shape of young branches Not angular Angular Not angular Lamina length (cm) 7–20 18–28 15–18 Lamina width (cm) 3–9 8–12 8–10 Pedicel length (mm) 5–7 4–5 3 Pedicel articulation 1 mm below the calyx about 1 mm below the calyx Directly below the calyx Calyx margin Entire 6–10 lobed Entire Calyx shape Cupuliform Cupuliform Flattened patelliform Pseudocorolla length (mm) 3–5 7–8 8 Number of ovules per locule 1 2 or 3 Many Fruit surface Smooth Ridged Smooth Fruit diameter (mm) 15–20 10–12 15 A new species of Rhaptopetalum (Lecythidaceae) from south-western Gabon 41 Taxonomic treatment Key to the Gabonese species of Rhaptopetalum 1 Leaf lamina exceeding 18 cm long and 10 cm wide ....................................2 – Leaf lamina up to 18 cm long and 10 cm wide ...........................................3 2 Ovary conical, pedicel 3—5 mm long, placentation axile ...... R. sindarense – Ovary dome-shaped, pedicel 8–10 mm long, placentation apical .................. ..........................................................................................R. pachyphyllum 3 Leaf base cuneate, slightly decurrent onto petiole .....................R. coriaceum – Leaf base rounded .......................................................................................4 4 Young branches glabrous, petiole 5—7 mm long, ovary loci multi-ovulate ... ................................................................................................R. belingense – Young branches puberulous, petiole 2—4 mm long, ovary loci uni-ovulate .. ...................................................................................................R. rabiense Rhaptopetalum rabiense Kenfack & Nguema, sp. nov. urn:lsid:ipni.org:names:77200426-1 Figs 1, 2 Type. GABON. Ogooué Maritime, 25-ha Rabi Forest plot, 1°55'37.57"S, 9°52'50.66"E, 23 m alt., 27 Aug 2014 (fl), Nguema et al. 2825a (holotype: LBV, iso- types: BR, MO, US, K, P) Diagnosis. Rhaptopetalum rabiense is similar to R. belingense by its dome-shaped ovary, its entire calyx margin, its apex placentation and smooth fruits, but differs by its pubescent (vs. glabrous) young branches, its longer pedicel (5–7 mm vs. 3 mm) articulated 1 mm below the calyx (vs. articulated directly below the calyx), and its uni- ovulated loci (vs. multi-ovulated) (Table1). Description. Tree 4–6 m tall, bole cylindrical, to 20 cm diameter at 1.3 m above- ground; bark pale brown, slash fibrous, pink in the outer part, yellowish in the inner part; young branches slender, rusty brown, densely puberulous, conspicuously lenti- cellate. Leaves distichous; petiole 2–4(6) × 2 mm, densely puberulous; lamina obovate to elliptic, coriaceous, abundantly punctate, 8–18(21) × (2.5)5–9 cm, acuminate to broadly acute at apex, slightly unequal and rounded at base; margin entire; midrib con- spicuous and flattened above, prominent and minutely puberulous beneath; secondary veins 8–11 pairs, plane above, prominent beneath, arching and joined towards the margin of the lamina. Inflorescence ramiflorous, axillary and supra-axillary, fasciculate, with 1–8 flowers. Bracts ovate, about 1 mm long. Flower bud ovoid to globose-oblong, rounded at apex, (2.5)3–4 mm long, pink to red directly above the calyx rim, light pink to whitish towards the apex. Pedicel in flower buds (2.5)3–5 mm, but generally 5–7 mm long in opened flowers, yellow-green, minutely puberulous to glabrescent, articulate directly beneath calyx. Calyx cupuliform, yellow-green, glabrescent to pu- David Kenfack & Diosdado Ekomo Nguema / PhytoKeys 128: 39–46 (2019)42 Figure 1. Rhaptopetalum rabiense A f lowering twig B close-up of the lower surface showing the indumentum and the punctate lamina C detail of inflorescence and stem showing lenticels D f lower bud E opened flower F f lower with pseudocorolla and stamens removed showing superior ovary G longitudinal section of F showing pendulous ovules H fruiting branch. A new species of Rhaptopetalum (Lecythidaceae) from south-western Gabon 43 berulous, the margin entire, 2–2.5 mm in diameter on the rim, receptacle about 1 mm long. Pseudocorolla fleshy, splitting into (3)4 lobes 2.5–4 mm long oblong to ovate lobes. Stamens 35(37), the filament light pink to whitish, about 0.3 mm, the poricidal anthers bright yellow, slightly arched towards the centre of the flower, 2–2.5 mm long; Figure 2. Rhaptopetalum rabiense A flowering branch B lateral view of the flower C flower view from above showing the poricidal anthers and the gynoecium D fruiting branch. Photographs by Diosdado Nguema. David Kenfack & Diosdado Ekomo Nguema / PhytoKeys 128: 39–46 (2019)44 ovary superior, globose, about 1 mm high and 1.5 mm diameter, 3–4-locular, each locule with 1 or 2 axile pendulous ovules. Style 3–4.5 mm long. Fruit a globose cap- sule, green, smooth, 15–20 mm diam., fruiting pedicel 5–7 mm long, seeds 8–12 × 5–8 mm. Phenology. Flowering August–October, Fruiting September–December. Geographic distribution. Rhaptopetalum rabiense is only known from the type locality, the Rabi forest (Figure 3). Habitat. Rhaptopetalum rabiense grows in old growth forest, on both terra firme dry and wet depressions, with elevation 20–50 m. Additional specimens examined. GABON. Ogooué Maritime: Rabi, 25-ha permanent plot, 24 m elev., 1°55'28.1"S, 9°52'48.26"E, 21 August 2013 (st), Nguema et al. 1743; Rabi, 25-ha permanent plot, 50 m elev., 1°54'51.36"S, 9°52'41.56"E, 28 October 2013 (st), Nguema et al. 1922; Rabi, 25-ha permanent plot, 50 m elev., 1°55'27.09"S, 9°52'41.56"E, 5 November 2013 (st), Nguema et al. 2057; Rabi, 25- ha permanent plot, 32 m elev., 1°55'37.57"S, 9°52'50.66"E, 2 September 2014 Figure 3. Type locations of Rhaptopetalum rabiense and the closely related species R. belingense in Gabon. A new species of Rhaptopetalum (Lecythidaceae) from south-western Gabon 45 (fl), Nguema et al. 2825B; Rabi, 25-ha permanent plot, 32 m elev., 1°55'37.57"S, 9°52'50.66"E, 2 September 2014 (fr), Nguema et al. 2825C; Rabi, 25-ha permanent plot, 32 m elev., 1°55'30.22"S, 9°52'42.18"E, 23 September 2014 (fl), Nguema et al. 2832; Rabi, 25-ha permanent plot, 32 m elev., 1°55'30.35"S, 9°52'41.79"E, 2 October 2014 (fl), Nguema et al. 2833; Rabi, 25-ha permanent plot, 61 m elev., 1°55'36.44"S, 9°52'46.61"E, 2 December 2014 (fr), Nguema et al. 2926. Preliminary conservation status. The conservation status of Rhaptopetalum rabiense was evaluated using the IUCN Red List Categories and Criteria Version3.1 (IUCN 2012). The extent of occurrence (EOO) and the area of occupancy (AOO), estimated using the web Geospatial Conservation Assessment Tool or GeoCAT (Bachman et al. 2011) and the auto-value cell size length of 2 km, were 0.214 km2 and 8.00 km2, respectively. These two values meet the criteria B1 (EOO < 100 km2) and B2 (AOO < 10 km2) for Critically Endangered, following the IUCN Red List Categories and Criteria Version 3.1 (IUCN 2012). The species is not under legal protection. The type locality is an oil and gas production field and, at the same time, a logging concession. These activities are likely to result in its population reduction and/or in a fragmentation of its range. R. rabiense in the studied plot has 299 individuals with dbh ≥ 1cm (12 individuals per hectare) and seems to be regenerating, based on diameter size class distribution. It is known only from its type locality and has not been recorded in the adjacent national parks of Loango National Park on the west and Moukalaba Doudou National Park on the east. We therefore assess R. rabiense with the preliminary IUCN Red List status of Critically Endangered CR B12ab(iii). Acknowledgements We are grateful to the Government of Gabon through the Centre National de la Re- cherche Scientifique et Technologique (CENAREST) for granting us permission to conduct the study and the Compagnie des bois du Gabon (CBG) for permission to establish the plot in their forest concession. The bulk of the financial and logistical support that led to the discovery of this new species was provided by Shell Gabon and Assala Energy, through the Center for Conservation and Sustainability of the Smith- sonian Conservation Biology Institute. Additional funding and technical support was provided by the Smithsonian Tropical Research Institute through the Forest Global Earth Observatory. We thank the personnel of the Institut de la Recherche en Écologie Tropicale (IRET) and the Herbier National du Gabon for their great support and con- tribution to the success of this work. We greatly appreciate the contribution of Gauthier Moussavou, Etienne Moumoulossi, Landry Tchignoumba, Prince Biessemou, Wilfried Mbading-Mbading, Gorky Villa and all other technicians who were involved in field- work. Special thanks to Alfonso Alonso, Lisa Korte, Hervé Memiaghe and Pulchérie Bissengou for their leading role in this project, to Alice Tangerini of the Smithsonian NMNH for the marvellous illustration of the new species and to Dr Duncan Kimuyu for the location map. This is contribution #190 of the Gabon Biodiversity Program. David Kenfack & Diosdado Ekomo Nguema / PhytoKeys 128: 39–46 (2019)46 References APG (2016) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society. https://doi. org/10.1111/boj.12385 Bachman S, Moat J, Hill AW, de Torre J, Scott B (2011) Supporting Red List threat assessments with GeoCAT: Geospatial conservation assessment tool. ZooKeys 150: 117–126. https:// doi.org/10.3897/zookeys.150.2109 Cheek M, Gosline G, Csiba L (2002) A New Species of Rhaptopetalum (Scytopetalaceae) from Western Cameroon. Kew Bulletin 57(3): 661–667. https://doi.org/10.2307/4110996 IUCN (2012) IUCN Red List Categories and Criteria: Version 3.1 (2nd edn). IUCN Gland and Cambridge. Letouzey R, White F (1978) Chrysobalanaceae–Scytopetalaceae – Flore du Gabon 24. 202 pp. Muséum National d’Histoire Naturelle, Paris. Mabberley DJ (2008) Mabberley’s plant-book: a portable dictionary of plants, their classifica- tions and uses (3rd edn). Cambridge University Press. Memiaghe HR, Lutz JA, Korte L, Alonso A, Kenfack D (2016) Ecological Importance of Small-Diameter Trees to the Structure, Diversity and Biomass of a Tropical Evergreen Forest at Rabi, Gabon. PLoS One 11(5): e0154988. https://doi.org/10.1371/journal. pone.0154988 Mori SA, Tsou C-H, Wu C-C, Cronholm B, Anderberg AA (2007) Evolution of Lecythi- daceae with an emphasis on the circumscription of Neotropical genera: Information from combined ndhF and trnL-F sequence data. American Journal of Botany 94(3): 289–301. https://doi.org/10.3732/ajb.94.3.289 Morton C, Mori S, Prance G, Karol KG, Chase MW (1997) Phylogenetic relationships of Lecythidaceae: A cladistic analysis using rbcL sequence and morphological data. American Journal of Botany 84(4): 530–540. https://doi.org/10.2307/2446029 Oliver D (1865) On four new genera of plants. Journal of the Linnean Society. Botany 8: 159–160. Prance GT, Jongkind CCH (2015) A revision of African Lecythidaceae. Kew Bulletin 70(1): 6. https://doi.org/10.1007/s12225-014-9547-4 Reveal JL (2011) Summary of recent systems of angiosperm classification. Kew Bulletin 66(1): 5–48. https://doi.org/10.1007/s12225-011-9259-y Takhtajan A (2009) Flowering plants. Springer Science & Business Media. https://doi. org/10.1007/978-1-4020-9609-9