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A checklist of vascular plants of Ewe-Adakplame Relic Forest in Benin, West Africa
DOI 10.3897/phytokeys.175.61467 , Volume: 175 , Issue: null , Pages: 151-174
Article Type: research-article, Article History

Covering 560.14 hectares in the south-east of Benin, the Ewe-Adakplame Relic Forest (EARF) is a micro-refugium that shows insular characteristics within the Dahomey Gap. It is probably one of the last remnants of tropical rain forest that would have survived the late Holocene dry period. Based on intensive field investigations through 25 plots (10 × 50 m size) and matching of herbarium specimens, a checklist of 185 species of vascular plant belonging to 54 families and 142 genera is presented for this forest. In addition to the name for each taxon, we described the life form following Raunkiaer’s definitions, chorology as well as threats to habitat. The family was the richest (20 species) followed by the (15 species). Life forms showed the preponderance of phanerophytes (88%). The Chorological spectrum was dominated by Guineo-Congolean species (66%). Species richness estimated were 200.52 ± 9.2808 for Bootstrap; 217.62 ± 14.5972; 224.16 ± 15.3725 and 242.67 respectively for Chao, Jacknife1 and Jacknife2. Bootstrap appears to be the estimation closer to the field records. In Benin, EARF is home for species described as West African forest bio-indicators and single location for , , , , and most of tribe species (, , and ) recorded in Benin. Our results provides baseline information for further in-depth analysis of vegetation history in Benin by raising the question on the past floristic connection of the Dahomey gap and community engagement in conservation.

Houngnon, Adomou, Gosling, and Adeonipekun: A checklist of vascular plants of Ewe-Adakplame Relic Forest in Benin, West Africa


At the continental level, African rain forests, primarily those of the Guineo-Congolean block, are the main centres of species diversity (White 1983; Lebrun 2001; Sosef et al. 2017; Droissart et al. 2018; Couvreur et al. 2021). However, in some regions of this block, landscape changes have been so severe that particular areas would have functioned as refugia, while diversity in surrounding areas would have experienced losses. This is probably the case with forest islands within the Dahomey Gap which is the dry corridor separating the West African rain forest into the Upper Guinean and Lower Guinean blocks (White 1983; Jenik 1994; Poorter et al. 2004). During the late Holocene dry period (3000–2500 yrs BP), the once continuous rain forest belt became fragmented and was reduced to isolated patches that would have persisted and survived as “small isolated humid pockets” (Dupont and Weinelt 1996; Salzmann and Hoelzmann 2005). In addition to these historical climatic oscillations, archaeologists and ecologists highlighted several proofs of human footprint such as metallurgy (cast iron), agriculture, pottery that would have gradually caused deforestation and may explain the phytogeographic status of the Dahomey gap in West Africa (Richards 1973; Paradis 1977; Wantchecon 1983; Brand 2001; Garnier et al. 2018). Indeed, this savanna intermingled with small forest patches within the Dahomey gap, is also seen as a cultural landscape, produced by humans for subsistence, security and/or worship uses of religious traditions (Juhé-Beaulaton 2010; Cousin 2018). Consequently, the vegetation of Benin which is supposed to be luxuriant is today largely dominated by farms, fallows and grasslands (Adjanohoun 1966; Jenik 1994; Sosef et al. 2017). One fifth of the original forests remain, fragmented into isolated patches (Poorter et al. 2004). Today, Benin is home to 2807 plant species in terms of floristic composition (Akoègninou et al. 2006). It is among the best explored botany countries of sampling completeness with 2460 species theoretically estimated between 2864 and 2889 species (Sosef et al. 2017). Despite this sampling effort, some species that have not yet been collected or reported may not be listed and therefore omitted. Either because they may have disappeared, following their habitat degradation, as was the case of Chrysobalanus icaco L. (Syn. C. atacoriensis A. Chev.), which would have disappeared following earthworks (Adjanohoun et al. 1989).

However in Benin, most of these remaining forest patches, although playing the role of a high conservation priority area for heritage plants, are still experiencing severe threats due to the lack of adequate conservation strategies (Oloukoï et al. 2007; Adomou et al. 2010). This is probably the case with Ewe and Adakplame Relic Forest (EARF) in the south east of Benin. Up to now, this relic still persists on a community land while showing insular characteristics with some rare and poorly known plant species. Earlier botanists who worked on this refugium include Chevalier (1910), Aubréville (1937) and Adjanohoun (1966). They noted the typical feature of the Ewe-Adakplame Relict Forest (EARF) described as a Timber-refuge of the time of tribal wars, as one having a considerable number of African rain forest species of Guineo-Congolean region comparable to those of Côte d’Ivoire (Adjanohoun et al. 1989, P. 20).

In this context, floristic details on EARF may be very useful for conservation purposes through restoration and rehabilitation of degraded land with native trees. Such information is necessary for further studies in biogeography and phylogeny on the one hand, to address the main speciation models and mechanisms that may apply across tropical Africa (Demenou et al. 2016, 2018; Couvreur et al. 2021), and on the other hand to reconstruct the history of Tropical Africa vegetation.

This paper aims to provide a comprehensive checklist of vascular plants occurring in EARF that will serve as baseline for understanding the history of this vegetation over millennia. By exploring the floristic composition of EARF, we can better appreciate the biogeographic status of some species previously reported by Achoundong (1996; 2000) as bio indicators in other West African forests located on either side of the Dahomey gap. The results could help (1) to better understand how the Dahomey Gap has affected the vegetation of this area and (2) to catalyze long-lasting conservation actions toward EARF.

Methods area

Study site

The EARF covers 560.14 hectares in the Kétou District in the south-east of Benin Republic at 07°27'59.195"N, 002°34'29.395"E (Fig. 1). This part of the country belongs to the Guineo-Congolean Region (White 1983; Adomou et al. 2006). The forest relic is located at the north-east of the depression of “Co” or “Lama” on the plateaus of low altitude that evolved on the pre-Cambrian base rocks (Adjanohoun et al. 1989). In Benin, the most important national protected areas are in the north. There are several other forests (albeit small) in the southern part of the country which are within the national protected areas network (e.g. gazetted forests of Dogo-Ketou, Pobe, Lama, Pahou) which are well-managed (Adomou et al. 2006). There is also the recent Transboundary biosphere reserve of Mono which is now part of the national protected areas network. However, EARF has not yet been included in this national protected areas network.

The mean annual rainfall in the EARF is between 900–1300 mm (Adjanohoun et al. 1989; CARDER 2002; Adomou et al. 2006) which contrasts to other similar African dense semi-deciduous forests. The rainfall recorded in Upper Guinea is between 1750–1900 mm (Martin 2008) in Côte d’Ivoire (West Africa) and annual rainfall measured around the Kakamega rain forest in East Africa was approximately 2215 mm (Cords 1987) and 1956 mm (Greiner 1991). Table 1 provides parameters such as temperature, relative humidity, vegetation and soil types of the study site. The landscape surrounding EARF is dominated by fallows, cultivation areas and housing. The vegetation is a mosaic of savanna with species of the Sudanian transition zone such as Adansonia digitata L., Stereospermum kuntianum Cham., Trichilia emetic Vahl, Annona senegalensis Pers., Vitex doniana Sweet, Parkia biglobosa (Jacq.) R.Br. ex G. Don, Dichrostachys cinerea (L.) Wight & Arn., Pterocarpus erinaceus Poir., Pericopsis laxiflora (Benth.) Meeuwen, Daniellia oliveri (Rolfe) Hutch. & Dalziel, Vitellaria paradoxa C.F. Gaertn., Sarcocephalus latifolius (Sm.) E.A. Bruce, Uvaria chamae P. Beauv., Vitex grandifolia Gürke and Andropogon gayanus Kunth (Biaou 2009; Armani et al. 2018). The total population of the villages of Ewe and Adakplame is 13,623 individuals with 2,078 households (INSAE 2016). The main activity is agriculture, followed by hunting, livestock breeding and local commerce.

Table 1.
Ecological characteristics of the study region.
Location6°25–7°30N Adjanohoun et al. (1989)
Adomou et al. (2006)
Annual rainfall900–1100 mmCARDER 2002, Adomou et al.(2006)
Rainfall trendBimodal Adjanohoun et al. (1989)
Rainy season(s)March–July & September–October Adjanohoun et al. (1989)
Adomou et al. (2006)
Dry seasonAugust and November–February Bani (2006)
Temperature24–37 °CCARDER (2002), Bani (2006)
Insolation2135 hCARDER (2002), Bani 2006
Relative humidity78–95%CARDER (2002), Bani (2006)
Climate typeSub-equatorial Adomou et al. (2006)
Length of plant growing season240 daysCARDER (2002), Bani (2006)
VegetationMosaic of Savanna Adjanohoun et al. (1989)
Adomou et al. (2006)
Soil typesFerralitic soils without concretionAdjanohoun et al. (1989), Bani (2006)
Altitude200–286 m above sea level Bani (2006)

Sampling and data collection

The inventory of EARF plant species was conducted from February 2014 to December 2017. The forest investigation was based on a vegetation map divided into 250,000 m2 (500 × 500 m) grids following 6 transects, each of 500 m width and 3000 m length. Transects were oriented south-north. The floristic sampling covered different components of the EARF (Fig. 1). At each stand, a topometer (Chaining Buddy, Fremaco Devices, Canada) with disposable filament was used to delimit quadrats of 10 × 50 m. The observation stands were set out at intervals of 100 m along each transect line and there was one quadrat per plot of 250,000 m2. In total, 25 forest quadrats of 500 m2 were floristically surveyed. To set a preliminary list of EARF flora, species identification was first based on our self-background during the sampling field work with photo captures (Olympus Digital Camera SP-620 UZ Silver and Samsung Galaxy S7 Android 6.0.1). This approach was combined with description session (on field and at the National Herbarium). Voucher specimens were systematically collected for specimens whose determination is confused. They were compared with voucher specimens of the national Herbarium. To access the systematic information notes, the botanical nomenclature followed the Analytical Flora of Benin (Akoègninou et al. 2006). The list of plant species recorded was compared to online resources such as the “Catalog of life” (Hassler 2020) and the Benin National Red List (Neuenschwander et al. 2011) in order to access botanical information notes and the conservation status of species.

Figure 1.
Location of the Ewe-Adakplame Relict Forest in Benin and positions of the sampling stands.

Data analysis

The Angiosperm Phylogeny Group (APG IV 2009) and the legume subfamilies currently accepted by the legume phylogeny working group (LPWG 2017) were used to update the list of the vascular plants recorded in EARF. The taxonomic plant diversity was assessed in terms of species, genus, and family richness. The species richness (S) corresponds to the number of species recorded from sampling plots (n = 25). We used the functions “specpool” and “estimateR” in R software (R-Core-Team 2016) for the main reason that S is sensitive to sample size and this may introduce bias in our estimations based on the field record. To circumvent this, we use species accumulation curve and different estimation methods in order to appreciate in the case of our field study, the best estimator which is closest to our field record (Palmer 1990; Colwell and Coddington 1994; Chiu et al. 2014). This approach also helps to assess the completeness of our sampling effort. Chao, first order jackknife, second order jackknife and bootstrap were then used to estimate the total number of species surveyed and to draw species accumulation curves (R-Core-Team 2016; Oksanen et al. 2017).

Life forms assessment followed Raunkiaer (1934); Hutchinson and Dalziel (1954–1972): Ph: phanerophytes subdivided into meg: megaphanerophyte (> 30 m tall), mes: mesophanerophyte (8–30 m), mph: microphanerophyte (2–8 m), nph: nanophanerophyte (0.5–2 m); Ch: chamaephyte, Hc: hemicryptophyte; Th: therophyte; G: geophyte (Gb: with bulb, Gr: with rhizome and Gt: with tuber); Ep: epiphyte and their climbing forms L: liana (Lmph, Lnph and Lmes, LGr, LHc).

The Chorology types were established after Hutchinson and Dalziel (1954–1972) and White (1983), as follows: GC: Guineo-Congolean, SG: Sudano/Guinean transition, GE: Lower Guinean, GO: Upper Guinean, TA: Tropical Africa, AM: Afro-Malagasy, Pan: Pantropical.

Data resources

The data underpinning the analysis reported in this paper are deposited in the Dryad Data Repository at (Houngnon and Adomou 2021).



Fig. 2A, B shows a panoramic view around and inside of EARF. Table 2 gives an overview of the vascular plant species recorded in the EARF. A total of 185 plant species distributed over 143 genera and 54 families was recorded (Table 2). With this figure, EARF conserves 6.59% of the national flora over 560.14 hectares of a community land. Of these, Rubiaceae was the most speciose family (20 species), followed by Fabaceae (15), Malvaceae (13), Apocynaceae (12), Sapindaceae (8) and Annonaceae (7). Capparaceae, Celastraceae, Dioscoreaceae, Putranjivaceae, Violaceae were each represented by five species. Among the 185 vascular plants of EARF 12% of the families (22) were represented by one species each. The genera Dioscorea, Drypetes and Rinorea, are represented by five species followed by genera Albizia, Cissus, Strychnos (4 species each) and Celtis and Diospyros (3 species each). EARF also provides habitat for Chrysophyllum welwitschii, (Not mentioned in the Flora), Cissus glaucophylla (Not mentioned in the Flora), Drypetes aframensis, (Not mentioned in the Flora), Drypetes afzelii, Drypetes gilgiana, Drypetes leonensis, Englerophytum oblanceolatum, Mansonia altissima, Nesogordonia papaverifera, Octolobus spectabilis, (Not mentioned in the Flora), Rinorea batesii, Rinorea brachypetala (Not mentioned in the Flora), Rinorea dentata, Rinorea ilicifolia, Rinorea kibbiensis, Vitex micrantha), (Not mentioned in the Flora) which appear to be confined to EARF that can be seen as the single location of their occurrence in Benin. Table 2 also describes the community data set using family, binomial, life-forms and Chorotypes. Some of these plant species are featured in Fig. 3A–K.

Table 2.
Vascular plants of Ewe-Adapklame relict forest in Benin with their binomial, family life-forms and Chorotypes [Life-forms are meg: megaphanerophyte (> 30 m tall), mes: mesophanerophyte (8–30 m), mph: microphanerophyte (2–8 m), nph: nanophanerophyte (0.5–2 m); Ch: chamaephyte, Hc: hemicryptophyte; Th: therophyte; G: geophyte (Gb: with bulb, Gr: with rhizome and Gt: with tuber); Ep: epiphyte and their climbing forms L: liana (Lmph, Lnph and Lmes, LGr, LHc) and chorotypes are GC: Guineo-Congolean, SG: Sudano/Guinean transition, GE: Lower Guinean, GO: Upper Guinean, TA: Tropical Africa, AM: Afro-Malagasy and Pan: Pantropical].
Scientific nameLife formsChorology typesVoucher specimens
Rhinacanthus virens (Nees) Milne. Readh. var. virens Ch GC Houngnon 3860
Cyathula prostrata (L.) Blume Th Pan Houngnon 3383
Scadoxus multiflorus (Martyn) Raf. subsp multiflorus Gb TA Houngnon 6724
Lannea nigritana (Sc. Elliot) Keay var. nigritana mes GO De Souza 1971 a
Spondias mombin L. mes Pan Maesen 7705
Artabotrys dahomensis Engl. & Diels.Lnph GE Houngnon 97e
Artabotrys velutinus Sc. ElliotLnph GC Maesen 6612
Monanthotaxis parvifolia (Oliv.) Verdc.Lnph GE Houngnon s.n.
Monodora tenuifolia Benth. mph GC Éq. Bot. 105d
Uvariodendron angustifolium (Engl. & Diels) R.E.Fr mph GC Houngnon 5571
Uvariopsis tripetala (Baker f.) G.E.Schatz Syn. Dennettia tripetala Baker f. mph GE Akoègninou 2201
Xylopia longipetala De Wild. & T. Durand mph GC Houngnon 4524
Alafia barteri Oliv.Lmph GC Chevalier 22841
Ancylobotrys scandens (Schumach. & Thonn.) PifchonLmph GC Chevalier 23456
Baissea zygodioides (K. Schum.) StapfLmph GC Houngnon 118c
Cryptolepis nigrescens (Wennberg) L. Joubert & Bruyns Syn. Parquetina nigrescens (Afzel.) BullockLmph GC Le Testu 297
Holarrhena floribunda (G. Don) Dur. & Schinz mph TA Houngnon 6574
Hunteria umbellata (K. Schum.) Hall. f. Syn. H. eburnea Pichon mph GC Aké Assi 20284
Landolphia hirsuta (Hua) PichonLmes GC Chevalier 23922
Marsdenia latifolia (Benth.) K. Schum.,Lmph TA Akoègninou 5438
Mondia whitei (Hook. f.) SkeelsLmph TA Adjakidjè 3007
Motandra guineensis (Thonn.) A. DC.Lmph TA Adjanohoun 102
Saba thompsonii (A. Chev.) PichonLmes GC Chevalier 22967
Secamone afzelii (Schultes) K. Schum.Lmph GC Essou 3208
Anchomanes difformis (Blume) Engl. (Syn. A. welwitschii Rendle) Gt GC Essou 1554
Cercestis mirabilis (N. E. Br.) Bogner Syn. Rhektophyllum mirabile N.E.Br. Ep GE Akoègninou 3299.
Pararistolochia goldieana (Hook. f.) Hutch. & Dalz.LGr GC Houngnon 4605
Dracaena arborea Bak mph GC Maesen 6340
Chromolaena odorata (L.) R. King & H. Robinson nph AM Sokpon B14
Gymnanthemum coloratum (Willd.) H. Rob. & B.Kahn mph SZAyichédéhou 395
Laggera crispata (Vahl) Hepper & J. R. I. Wood. Th TA Maesen 6746
Newbouldia laevis (P. Beauv.) Seem. ex Bureau mph GC Houngnon 3087
Ehretia cymosa Thonn. mph GC Houngnon 5081
Celtis mildbraedii Engl. mes GC Essou 1648
Celtis philippensis Blanco Syn. C. brownii Rendle mph GC Houngnon 2783
Celtis zenkeri Engl. meg GC Sokpon 852
Trema orientalis Syn. T. guineensis mph GC Houngnon 1714d
Capparis brassii DC. Syn. C. thonningii Schum.Lnph GC Maesen 6701
Capparis erythrocarpos Isert var. erythrocarpos nph GC Esson 1087
Maerua duchesnei (De Wild.) F. White Syn: Ritcheia duchesnei (De Wild.) Keay mph GC Houngnon 229a
Ritchiea capparioides (Andr.) Britten var. capparoides Lnph GC Houngnon 4200
Ritchiea erecta Hook. f. Syn. R. pentaphylla Gilg & Bened. nph GE Aké Assi 20288
Loeseneriella africana (Willd.) N.Hallé var. africana Syn. Hippocratea Africana (Willd.) Loes.Lmph Pan Houngnon 6573
Reissantia indica (Willd.) N. HalléLnph Pan Akoègninou 4026
Salacia longipes (Oliv.) N. Hallé nph TA Akoègninou 3291
Salacia pallescens Oliv. nph GC Sokpon 2221
Simicratea welwitschii (Oliv.) Syn. S. welwitschii (Oliv.) N. HalléLmph GC Essou 1467
Combretum racemosum P. Beauv.Lmph GC Le Testu 191
Cyanotis lanata Benth. Ch SG Morton A4570
Cnestis ferruginea Vahl ex DC. nph GC Houngnon 3051
Cnestis corniculata Lam. Syn. Cnestis longiflora Schellenb.Lmph GO Chevalier 22828
Rourea coccinea (Bak.) Jongkind syn. Byrsocarpus coccineus Thonn. & Schumach. nph TA Chevalier 22798b
Calycobolus africanus (G. Don) heineLnph GC Adjakidjè 4111
Ipomoea mauritiana Hall. f.Lmph Pan Oumorou 740
Coccinia grandis (L.) VoigtLnph GC De Souza & Paradis 444a
Lagenaria breviflora (Benth.) Roberty Syn. Adenopus breviflorus Benth.Lmes TA Houngnon 443a, 1518a
Luffa cylindrica (L.) M. J. Roem syn. Luffa aegyptiaca MillLnph Pan Houngnon 453a
Momordica charantia L.Lnph GC Houngnon 1676
Dichapetalum madagascariense Poir. Syn. D guineense (DC.) KeayLmph GC Adomou 95
Tapura fischeri Engl. mph GC Houngnon 1878a
Dioscorea bulbifera L. var. bulbifera Gt Pan Essoun 3316
Dioscorea lecardii De Wild. Gt SZPauwels 8139
Dioscorea odoratissima Pax Syn. D. praehensilissensu F.T.A, F.W.T.A Gt SG Chevalier 24154
Dioscorea quartiniana A. Rich. Gt SZSokpon 2329
Dioscorea sagittifolia Pax syn. D. abyssinica Hochst. ex Kunth Gt SZParadis et Houngnon: 619d
Diospyros abyssinica (Hiern) White mes GC Houngnon 627b
Diospyros monbuttensis Gürke mph GC Houngnon 629c
Diospyros soubreana F. White nph GC Houngnon 2824
Erythrococca anomala (Juss. ex Poir.) Prain nph GC Houngnon 3345
Mallotus oppositifolius (Geisel.) Müell. Arg. var. oppositifolius nph AM Adjakidjè & Akoègninou 590c
Tragia senegalensis Müll. Arg.Lnph SG Adjakidjè 2803
Caesalpinoideae (Mimosoid clade)
Acacia pennata (L.) Willd.Lmph TA Essou 1672
Acacia polyacantha Willd. subsp. Campylacantha (Hochst. ex A. Rich.) Brenan mes SZMaesen 6703
Albizia adianthifolia (Schum.) W. Wight var. adianthifolia mes GC Adjakidjè 4163
Albizia glaberrima (Schum. & Thonn.) Benth. mph GC Houngnon 6532
Albizia ferruginea (Guill. & Perr.) Benth. mes GC Paradis & Houngnon 933a
Albizia zygia (DC.) J. F. Macbr. mes GC Houngnon 936d
Mezoneuron benthamianum (Baill.) Herend. & ZarucchiLmph GC Paradis & Houngnon 277c
Detarium senegalense J.F. Gmel. mes GC Houngnon 268e
Dialium guineense Willd. mes GC Spire 118
Faboideae / Papilionoideae
Abrus precatorius L.Lnph Pan Houngnon 1423g
Dalbergia lactea VatkeLmph GE De Souza & Paradis 1239e
Dalbergia melanoxylon Guill. Perr. mph SG Adomou 167
Desmodium salicifolium (Poir.) DC. var. salicifolium nph GC Frahm-Leliveld 57139
Dolichos trilobus LnphSZAdomou 80
Millettia thonningii (Schum. & Thonn.) Bak. mph GC Essou 1164
Stachyanthus occidentalis (Keay & Miège) Boutique syn. Neostachyanthus occidentalis Keay & MiègeLnph GO Essou 1102
Clerodendrum capitatum (Willd.) Schum. & Thonn.Lmph GC Lisowski 0-929
Hoslundia opposita Vahl nph AM Pauwels 8286
Premna quadrifolia Schum. & Thonn. nph GO Sokpon 1068
Vitex micrantha Gürke* mes GC Adomou s.n.
Hugonia platysepala Welw. ex Oliv.Lmph GC Paradis & Houngnon 831a
Strychnos barteri Soler.Lmes GC Paradis & Houngnon 838a
Strychnos floribunda GilgLmes GC Maesen 6821
Strychnos nigritana Bak.Lmes GC Akoègninou 3289
Strychnos splendens GilgLmes GC Houngnon 835b
Abutilon mauritianum (Jacq.) Medic. Ch TA De Souza & Paradis 851a
Ceiba pentandra (L.) Gaertn. meg Pan Houngnon 188a
Hibiscus lunariifolius Willd.Lmph Pan Adomou s.n.
Hibiscus owariensis P. Beauv. nph GC Paradis et Houngnon 856a
Cola milfenii K. Schum. mph GC Houngnon 4399
Glyphaea brevis (Spreng.) Monachino mph GC Houngnon 2036e
Grewia carpinifolia Juss. mph GC Houngnon 1446f
Mansonia altissima (A. Chev.) A. Chev. var. altissima* mes GC Houngnon 1309a ; 4322
Nesogordonia papaverifera (A. Chev.) syn N. kabengaensis (K.Schum.)* mph GC Houngnon 13l0a
Octolobus spectabilis Welw. Syn. O. angustatus Hutch.* nph GC Adomou s.n.
Pterygota macrocarpa K. Schum *. mph GC Houngnon 4321
Sterculia tragacantha Lindl. mes GC De Souza & Houngnon 188d
Triplochiton scleroxylon K. Schum. meg GC Chevalier 22819
Memecylon afzelii G. Don var. afzeliiLnph GC Houngnon 897c
Warneckea memecyloides (Benth.) Jac. Fél Syn. Memecylon memecyloides (Benth)Lmph GC De Souza & Paradis 900a
Trichilia prieureana A. Juss. subsp. prieureana mph GC Adomou 90
Dioscoreophyllum cumminsii (Stapf) DielsLnph GC Houngnon 919a
Rhigiocarya racemifera MiersLnph GC Maesen 6820
Tiliacora funifera (Miers) Oliv.Lmph GC De Souza 92li
Triclisia subcordata Oliv.Lnph GC Sokpon 31
Antiaris toxicaria Lesch. meg GC Essou 1547
Ficus recurvata De Wild. Syn. Ficus goliath A. Chev. mes GC Adomou s.n.
Ficus ovata Vahl, Ep GC Adomou s.n.
Milicia exelsa (Welw.) Berg Syn. Chlorophora excelsa (Welw.) benth. meg GC Chevalier 23169
Olax subscorpioidea Oliv. var. subscorpioidea mph GC Houngnon 7652
Schrebera arborea A. Chev. mes GC Akoègninou 2187
Opilia amentacea Roxb. Syn. O. celtidifolia (Guill. & Perr) Endl.,LmphSZAdjakidjè 1477
Microdesmis keayana J. Léonard, syn. M. puberula Hook. f. mph GC Pauwels 8298
Adenia cynanchifolia (Benth.) HarmsLmph GE Adomou s.n.
Adenia lobata (Jacq.) Engl.Lmph GC Essou 1637
Hilleria latifolia (Lam.) H. Walt. Ch AM Adomou 129
Acroceras gabunense (Hack.) Clayton* Th GC Mission ACCT/Bénin 2165
Olyra latifolia L. nph GC Houngnon 720c
Oplismenus hirtellus (L.) P. Beauv. subsp. Hirtellus Ch SG De Souza & Paradis 722a
Streptogyna crinita P. Beauv. Gr GC Houngnon 765b
Carpolobia lutea G. Don mph GC Maesen 6617
Drypetes aframensis Hutch.* mph GO Adomou s.n.
Drypetes afzelii (Pax) Hutch.,* mes GO Houngnon 177 la
Drypetes floribunda (Müll. Arg.) Hutch. mph GC Houngnon 4266
Drypetes gilgiana (Pax) Pax & Hoffm.* nph GC Akoègninou 2196
Drypetes leonensis Pax,* mes GC Houngnon 1771b
Lasiodiscus mannii Hook. f. mph GC Houngnon 1329b
Aidia genipiflora (DC.) Dandy mph GC Maesen 6611
Chassalia kolly (Schumach.) Hepper nph GC Maesen 6358
Coffea ebracteolata (Hiern) BrenanLnph GC Lejoly&Ganglo 2
Cremaspora triflora (Thonn.) K. Schum.Lmph GC Maesen 6284
Leptactina involucrata Hook. f.Lnph GC Adomou s.n.
Gardenia nitida Hook. mph GC Adomou 73
Hymenodictyon floribundum (Steud. & Hochst.) B.L.Rob. mes GC Sinsin 2863
Keetia hispida (Benth.) BridsonLmph GC Adomou s.n.
Morinda lucida Benth. mph Pan Maesen 6651
Oxyanthus pallidus Hiern nph GC Adomou s.n.
Oxyanthus speciosus DC. subsp. speciosus nph GC Essou 2496
Pavetta corymbosa (DC.) F. N. Williams mph SG Sokpon 1884
Pouchetia africana DC. nph GC Houngnon 6659
Psydrax horizontalis (K. Schum. & Thonn.) BridsonLmph SG Maesen 6710
Psydrax parviflora (Afzel.) Bridson nph GO Maesen 6287
Rothmannia longijlora Salisb mph GC Le Teslu 101
Rothmannia urcelliformis (Hiern) Bullock ex Robyns mph GC Dansi TW 50799
Rytigynia canthioides (Benth.) Robyns mph GC Adomou s.n.
Vangueriella nigerica (Robyns) Verdc. Syn. Vangueriopsis nigerica Robyns mph SZMaesen 6315
Vangueriella spinosa (Schumach.&Thonn.)Verdc. Syn. Vangueriopsis spinosa Hepper mph SZAdomou 32
Zanthoxylum leprieurii Guill. & Perr. Syn. Fagara angolensis Engl. mph GC Houngnon 535a
Zanthoxylum zanthoxyloides (Lam.) Zepernick & Timber mph SG Essou 2396
Dovyalis zenkeri Gilg (+) Syn. D. afzelii Gilg. (+) nph GO Houngnon 1364a
Flacourtia indica (Burm. f.) Merr. Syn. Flacourtia flavescens Willd. mph GC Houngnon 6606
Allophylus africanus P. Beauv. mph GC Houngnon 4037
Allophylus spicatus (Poir.) Radlk. mph GC Houngnon 4037
Blighia sapida KoenigmPh Pan Houngnon 5472
Blighia unijugata Bak. mph GC Paradis & Houngnon 1693d
Deinbollia pinnata (Poir.) Schumach. & Thonn. nph GC Maesen 6397
Lecaniodiscus cupanioides Planch. mph GC Maesen 6310
Majidea forsteri (Sprague) Radlk. meg GC Houngnon 1254a
Pancovia bijuga Willd. mph GC Houngnon 4978
Chrysophyllum welwitschii Engl.* (+)Lnph GC Adomou s.n.
Englerophytum oblanceolatum (S.Moore) T.D.Penn. syn. Bequaertiodendron oblanceolatum* (S.Moore) Heine & J. H. Hemsl. nph TA Maesen 6154
Pouteria alnifolia (Baker) Roberty Syn. Malacantha alnifolia (Baker) mph GC Sokpon 1915
Smilax anceps Willd.Syn. S. kraussiana MeissnerLGr TA Chevalier 24225
Solanum terminale Forssk. Subsp inconstans (C.H. Wright) HeineLmph GC Yédomonhan 173
Chaetachme aristata Planch. mph GC Houngnon 1784c
Rinorea batesii Chipp, Kew Bull. 293 (1923). nph GC Adomou 83
Rinorea brachypetala (Turcz.) Kuntze nph GC Adomou s.n.
Rinorea dentata (P.Beauv.) Kuntze mph GC Houngnon
Rinorea ilicifolia (Welw. ex Oliv.) Kuntze * nph GC Adomou 109
Rinorea kibbiensis Chipp. nph GC Paradis & Houngnon 1347a
Cissus glaucophylla Hook. f.Lnph GC Adomou s.n.
Cissus petiolata Hook. f.Lnph GC Adjakidjè 2976
Cissus populnea Guill. & Perr. var. populnea LHcSZHoungnon 68d
Cissus quadrangularis L.LmphSZHoungnon 5105
*: Plant species restricted to Ewe Adakplame Relict Forest (+): Non recorded
Figure 2.
Panoramic view of Ewe-Adakplame Relict Forest A forest ecosystem in contact with Ewe village’s (Olympus photo A. Houngnon 2014) B forest gap with Momordica charantia carpet (Samung photo A. Houngnon 2016).
Figure 3.
Common species of Ewe-Adakplame Relict Forest ADrypetes gilgiana (Photo of Alfred Houngnon 2017) BTriplochiton scleroxylon (Samsung photo A. Houngnon 2017) CEnglerophytum oblanceolatum (Olympus photo A. Houngnon 2014) DMansonia altissima (Olympus photo A. Houngnon 2014) EUvariopsis tripetalaFCeiba pentandra (Olympus photo A. Houngnon 2014) GAnchomanes welwitschii (Samsung photo A. Houngnon 2015) HAbrus precatorius (Samsung photo A. Houngnon 2016) IVitex micrantha (Samsung photo A. Houngnon 2016) JMomordica charantia (Samsung photo A. Houngnon 2016) KDioscoreophyllum cumminsii (photo A. Adomou 2011).

Life form spectrum

The most common life forms were phanerophytes (88%), containing, 3% of mega phanerophytes (meg) which are very large forest trees, 14% of mesophanerophytes (mes) or medium-sized forest trees, 43% of microphanerophytes (mph) or small forest trees and 28% of shrubs gathered into nanophanerophytes (nph). We recorded 33% of lianas, 6% of geophytes and 6% for chamaephyte, therophyte, epiphyte, hemicryptophyte (Fig. 4). The microphanerophytes were most representative among phanerophytes. The tree layer was discontinuous and composed of Celtis mildbraedii (Cannabaceae), Triplochiton scleroxylon (Malvaceae), Antiaris toxicaria (Moraceae), Celtis zenkeri (Cannabaceae), Dialium guineense (Fabaceae), Ceiba pentandra (Malvaceae), Mansonia altissima (Malvaceae), Milicia exelsa (Moraceae), and Nesogordonia papaverifera (Malvaceae).

Figure 4.
Life form spectrum of the Ewe-Adakplame relict forest. Erects are represented by Ph: Phanerophytes including megaphanerophytes (meg), mesophanerophytes (mes), microphanerophytes (mph), nanophanerophytes (nph), G: Geophytes are: Gb: with bulb, Gr: with rhizome and Gt: with tuber Ch: Chamaephytes, Th: Therophytes, Ep: Epiphytes, Hc: Hemicryptophytes. Climbing forms are L: Lianas (mph, nph and mes, Gr, Hc).

Chorology of Ewe-Adakplame relict forest

The most representative chorotypes (Fig. 5) included Guineo-Congolean species (66%), followed by 14% of wide distribution species including Tropical Africa (TA) and Pantropical (Pan) plant species. Upper Guinea species included plants such as Uvariopsis tripetala Syn. Dennettia tripetala (Annonaceae), Drypetes aframensis (Putranjivaceae tribe Drypeteae), Stachyanthus occidentalis Syn. Neostachyanthus occidentalis (Icacinaceae), Lannea nigritana var. nigritana (Anacardiaceae), Psydrax parviflora (Rubiaceae), Premna quadrifolia (Lamiaceae), Cnestis corniculata (Connaraceae). Monanthotaxis parvifolia (Annonaceae), Artabotrys dahomensis (Annonaceae), Dalbergia lactea (FabaceaeFaboideae), Ritchiea erecta Syn. R. pentaphylla (Capparaceae) and Cercestis mirabilis Syn. Rhektophyllum mirabile (Araceae) are among Lower Guinea species.

Figure 5.
Chorological spectrum of the Ewe-Adakplame Relict Forest. GC: Guineo-Congolean, SG: Sudano/Guinean transition, GE: Lower Guinean, GO: Upper Guinean, TA: Tropical Africa, AM: Afro-Malagasy and Pan: Pantropical.

Species richness estimations

The counted number of plant species for the EARF was 185. This corresponds to the species richness (S) or the number of species that has been recorded from plot sampling and listed in Table 2. The species richness estimations as per Bootstrap, Chao, Jacknife1 and Jacknife2 were respectively 200.52 ± 9.2808; 217.62 ± 14.5972, 224.16 ± 15.3725 and 242.67. We can see that the species richness estimates differ strongly giving a range of 200.52–242.67 species. The species accumulation curves in Fig. 6 show that they were hardly tending towards the asymptote and are still climbing at the right-hand end signifying that the sampling effort was insufficient. This suggests that the sampling has not captured nearly all the species in EARF and that many species were missed (on average approximately 16 species (± 9.2808) for Bootstrap, 33 species (± 14.5972) for Chao, 39 species (± 15.3725) for Jacknife1 and 58 species for Jacknife2.

Figure 6.
Species richness and richness estimations (Chao, first order jackknife, second order jackknife and bootstrap) (y-axis) in relation to sample size (x-axis) at the Ewe-Adakplame relict forest.


The Ewe-Adakplame Relict Forest corresponds to the semi-deciduous forest type, which was described in Benin as the only Drypetes aframensis-Nesogordonia papaverifera community (Adomou et al. 2009). Guineo-Congolean species are abundant (66%) although the EARF is located in a matrix of savanna-dominated vegetation. Guineo-Congolean species accounted for 33% in riparian forests of Benin (Natta 2003), 61.7% in gallery forests of the Hippopotamus Pond Biosphere Reserve at Burkina Faso (Bélem and Guinko 1998), and 70 to 75% in gallery forests at Lamto (southern Côte d’Ivoire) (Devineau 1975). The overall plant species composition makes EARF floristically comparable to the moist semi-deciduous forest of Nigeria (Lower Guinea) (Richards 1939) and the Celtis spp.-Mansonia altissima community of Côte d’Ivoire (Upper Guinea) (Guillaumet and Adjanohoun 1971). Guillaumet and Adjanohoun (1971) also pointed out that the dominance of Cannabaceae (previously Ulmaceae) and Malvaceae (previously Sterculiaceae) in the Upper and Lower Guinea forests offers evidence that West African semi-deciduous forests are at climatic climax. These indicator families were also reported as characteristics of the semi-deciduous forests in Ghana (Vooren and Sayer 1992) and Côte d’Ivoire (Swaine 1996) within the Upper Guinea zone. This high proportion of Guineo-Congolean species shows the floristic uniqueness of EARF and highlights its great importance in Benin which landscape is savanna dominated.

Unlike Palmer (1990) who showed that Jack 1 is the most precise and least biased, it is rather the Bootstrap estimator (200.52 ± 9.2808) that seems to be closer to our field results (S = 185 species). The Bootstrap value is also close to estimates of Adomou et al. (2010) who assessed the specific richness of EARF around 200 species. This is what justifies the calculation of the four estimation methods (Chao, first order jackknife, second order jackknife and bootstrap ) and not only one as Palmer (1990) would have demonstrated. In our study, the species accumulation curves were calculated with estimators (Chao, Jack 1, Jack 2 and Bootstrap) and showed a change in species richness without flatten off at the right hand. The Bootstrap appears to be the best estimator which is closest to EARF plant richness estimated by Adomou et al. (2010). The Fig. 6 show that species accumulation curves were hardly tending towards the asymptote and are still climbing at the right hand end signifying that the sampling effort was insufficient. This suggests that the sampling did not capture all the species in EARF. The shape of the species accumulation curves should plateau for large numbers of sites sampled. However, the number of observed species will typically be smaller than the true number of species. Since species richness depends on sample size, we can expect that we will not have recorded all the species that occur in the survey area. So, the Species accumulation curves were used to ascertain range in values obtained with the different methods and we can expect that the correct total richness lies somewhere within that range. Many species will always remain unseen or undetected in a collection of sample plots. It is like the case of Chrysophyllum welwitschii (Sapotaceae) and Drypetes aframensis which, although reported in EARF (Adomou 2005), has not been recorded since 2014. Drypetes aframensis (Salicaceae) is also not mentioned in the Benin Flora. From a physiognomic point of view, it is important to underline that it is sometimes extremely difficult to survey some areas because of the thickness of the vegetation which can be very inaccessible. Other places are severely affected by human presence leading to very sparse vegetation or gap areas in the heart of the forest with completely isolated forest tree species. This is also the case of the periphery cleared by human boundaries encroachment and so many activities often carried out illegally. These constraints have often influenced the layout and the number of sampled sites. This also proves that despite the botanical sampling effort of Benin (Sosef et al. 2017), some priority species for conservation have either not yet been collected or reported and therefore could be omitted.

The connection of EARF with the West African forests blocks located on both side of the Dahomey Gap is emphasized here by the high proportion of Guineo-Congolean species recorded (66%). The high rate of phanerophytes and their phytochories testifies to the floristic originality of EARF in a crop and savanna dominated landscape. This justifies the physiognomic and floristic links of EARF with the two Guinean and Congolia forest blocks and substantiates the hypothesis that EARF is a remnant of the dense forests which were once a continuous block from west to central Africa as demonstrated by numerous palynological studies (Tossou 2002; Salzmann and Hoelzmann 2005) and also phylogeography (Demenou et al. 2016). The floristic link of the EARF with the West African semi-deciduous forest is also best highlighted by the high representation of many Upper Guinean endemic species belonging to the families of Cannabaceae (Celtis mildbraedii, C. zenkeri and C. prantlii), Malvaceae (Triplochiton scleroxylon, Nesogordonia papaverifera, Mansonia altissima, Pterygota macrocarpa, Octobolus spectabilis and Sterculia tragacantha), and Putranjivaceae (Drypetes floribunda, D. gilgiana and D. aframensis ). This record provides strong evidence for past floristic connections with the West African rain forest zone which is consistent with paleovegetation reconstructions indicating that the tropical African rain forest formed a single block during the Holocene Humid Period (c. 9000–4500 yr BP) (Tossou 2002; Salzmann and Hoelzmann 2005; Demenou et al. 2018). Furthermore, the richness of EARF in Rinorea species (R. batesii, R. brachypetala, R. dentata, R. kibbiensis and R. ilicifolia ) and their abundance are unique in the country. According to Akoègninou et al. (2006), Rinorea batesii Chipp, Rinorea ilicifolia (Welw. Ex OIiv.) Kuntze, Rinorea dentata are common in West, Central and East Africa and some of them in Madagascar. However, in Benin most of them are rare and are only found in EARF. Rinorea brachypetala , although it has been reported by Adomou (2005), was not mentioned in the National Flora (Akoègninou et al. 2006). Rinorea species are described as good indicators for West African semi-deciduous forests in a climax state (Achoundong 2000). The strong representation of Rinorea spp., the Cannabaceae (previously Ulmaceae) and the Malvaceae (previously Sterculiaceae) substantiate the view of Guillaumet and Adjanohoun (1971), who considered this forest type as the climatic climax or primeval type of semi-deciduous forest in West Africa. With this floristic composition, EARF can be seen as a unique West African rain forest refuge in a matrix of savanna-dominated vegetation in Benin.

In contrast, the surrounding vegetation at the immediate edge of EARF is composed of savanna species (Fig. 7A–J) from the Guineo-Sudanian transition zone such as: Adansonia digitata L. (Malvaceae), Stereospermum kunthianum Cham. (Bignoniaceae), Trichilia emetic Vahl (Meliaceae), Annona senegalensis Pers. (Annonaceae), Vitex doniana Sweet (Lamiaceae), Parkia biglobosa (Jacq.) R.Br. ex G. Don (Fabaceae-Caesalpinioideae (mimosoid clade)), Dichrostachys cinerea (L.) Wight & Arn. (Fabaceae- Caesalpinioideae (mimosoid clade)), Pterocarpus erinaceus Poir. (Fabaceae-Faboideae), Pericopsis laxiflora (Benth.) Meeuwen (Fabaceae-Faboideae), Daniellia oliveri (Rolfe) Hutch. & Dalziel (Fabaceae-Detarioideae), Sarcocephalus latifolius (Sm.) E.A. Bruce (Rubiaceae) and Andropogon gayanus Kunth (Poaceae). The landscape is characterized by two basin ecosystems with clear dissimilarity combining forest/savanna and crop areas in stable equilibrium (Figs 8A, B). This makes EARF a special site of rich biodiversity and emphasizes the vital role the forest plays as a corridor of transition conducive to resilience and the flow of genes for ecosystem equilibrium.

Figure 7.
Species collected in the surrounding zone of Ewe-Adakplame Relict Forest AAdansonia digitata (Samsung photo A. Houngnon 2015) BPericopsis laxiflora (Samsung photo A. Houngnon 2016) CTrichilia emetic (Samsung photo A. Houngnon 2016) DAnnona senegalensis (Olympus photo A. Houngnon 2014) EVitex doniana (Samsung photo A. Houngnon 2016) FParkia biglobosa (Samsung photo A. Houngnon 2016) GDichrostachys cinerea (Samsung photo A. Houngnon 2016) HPterocarpus erinaceus (Samsung photo A. Houngnon 2016) IDaniellia oliveri (Samsung photo A. Houngnon 2016) and JAndropogon gayanus (Samsung photo A. Houngnon 2017).

In total, we counted thirteen species restricted to one site in EARF. This is higher than the nine species previously reported by Adomou et al. (2010) in the EARF. Our record represents 15.4% of species with high conservation priority, thus describing EARF as being one of the richest sites in range-restricted plant species of Benin. This increase in range-restricted species can be explained by the fact that species with a high scarcity index are vulnerable and could disappear if biodiversity sanctuaries that protect them disappear (Juhé-Beaulaton 2010). Indeed, during the last three decades in Benin, some forests areas have been cleared with an annual degradation rate of 70,000 hectares per year (PNF Bénin 2004). This habitat loss has considerably narrowed the survival places where rare species were previously recorded.

Figure 8.
Ewe Adakplame Relict Forest in a matrix of savanna and agriculture landscape A forest edge affected by anthropogenic activities (Samsung photo A. Houngnon 2017) B Landscape of fallow and field around the edge of the forest ecosystem (Olympus photo A. Houngnon 2016).

Some of these species found in the single location of EARF within Benin (e.g., Acroceras gabunense, Chrysophyllum welwitschii, Dovyalis afzelii, Drypetes aframensis, Drypetes gilgiana, Englerophytum oblanceolatum, Mansonia altissima, Nesogordonia papaverifera, Octolobus spectabilis, Pterygota macrocarpa, Rinorea ilicifolia, Rinorea kibbiensis and Vitex micrantha ) may gain more attention in the National Red List (Neuenschwander et al. 2011). Among them, there are many globally threatened species as the case of Nesogordonia papaverifera and Mansonia altissima, respectively reported as vulnerable (VU) and endangered (EN) by IUCN (2002) and later, were both assessed in Benin as critically endangered (CR) by Adomou et al. (2010) who considered EARF as sites with high concentration of threatened plant species in Benin. Moreover, the impact of harvesting on the survival of the most endangered species has been long ignored while many of them are not domesticated and many species uncharacterized. The case of Mansonia altissima is of urgent concern because its population is almost completely depleted, since it is locally used for roofing poles. Englerophytum oblanceolatum (Sapotaceae), which is not listed on the National Red List of Benin also tends to be concentrated in EARF (Houngnon 2014). Unfortunately, most of Benin Forest is still under severe threat due to expansion of towns, agricultural and fallow (Oloukoï et al. 2007) that are narrowing the natural habitat and leading to a massive loss of many of the local biodiversity taxa. To this end, since 2014, we have been trying to raise awareness among local communities from the villages of Ewe and Adakplame through participative action toward nursery establishment (Houngnon 2014) and vegetative propagation of native tree (Houngnon 2015) in order to rehabilitate the degraded lands and areas that could potentially be sensitive for the EARF durability.


The importance of the flora of EARF testifies to its role in conserving forest biodiversity in the Dahomey gap corridor. This justifies its peculiarity and the relevance of this baseline vegetation information that could be used as complete range taxa that may allow us to test the forest refuge hypothesis against alternative speciation models across ecological gradients. As it happens, the management of the forest of this type, also raises the question of deepening interactions linking human environment in order to better understand the actual role that humans would have played in shaping ecosystems in the Dahomey gap since millennia. So, it would be interesting to understand the interplay between locals and EARF in order to explain its persistence in this savanna dominated landscape. Therefore, the actions to be considered following this checklist of EARF must take into account the community’s engagement in rehabilitating the degraded lands inside and around EARF.


We are grateful to the Rufford Foundation for financial field assistance and the University of Amsterdam for the publication fees. We thank especially François Romazzotti and Professeur Angel Argiles for their assistance and the local communities of Ewe and Adakplame villages for their collaboration. The authors thank David Goyder, Kolawolé V. Salako and Thomas Couvreur for their contribution and their constructive comments that improved substantially the quality of this paper.


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