Introduction

Vepris Comm, ex A. Juss. (Rutaceae–Toddalieae), is a genus with 86 accepted species, 22 in Madagascar and 65 in Continental Africa with one species extending to Arabia and another endemic to India (Plants of the World Online 2018). Seventeen species were recorded from Cameroon (Onana 2011), rising recently to 20 (Onana & Chevillotte 2015), but several more remain undescribed. Vepris are easily recognized in continental Africa. They differ from all other Rutaceae in continental Africa because they have digitately (1-)3(-5)-foliolate (not pinnate) leaves, and unarmed (not spiny) stems. However, in Madagascar, the genus Melicope J. R. Forst. & G. Forst, also has these features.

The genus Vepris consists of evergreen shrubs and trees, predominantly of tropical lowland evergreen forest, but with some species extending into submontane forests and fewer still into drier forests and woodland.

Species of Vepris in Africa extend from S Africa, e.g. V. natalensis (Sond.) Mziray, to the Guinean woodland in the fringes of the Sahara desert [V. heterophylla (Engl.) Letouzey], Mziray (1992) subsumed the genera Araliopsis Engl., Diphasia Pierre, Diphasiopsis Mendonça, Oricia Pierre, Teclea Delile and Toddaliopsis Engl. into Vepris, although several species were only formally transferred subsequently (e.g. Cheek & al. 2009; Onana & Chevillotte 2015). Mziray's conclusions were confirmed by the molecular phylogenetic studies of Morton (2017). She studied about 14 taxa of Vepris, mainly those from E Africa.

Vepris species are often indicators of good quality, relatively undisturbed evergreen forest because they are not pioneers (Cheek, Onana pers. obs. 1992–2016). Due to their essential oils, several species are known for their traditional medicinal value (Burkill 1997). Burkill detailed the uses, essential oils and alkaloids known from five species in W Africa: V. afzelii (Engl.) Mziray (as Teclea afzelii Engl.), V. heterophylla (as T. sudanica A. Chev.), V. hiernii Gereau (as Diphasia klaineana Pierre), V. suaveolens (Engl.) Mziray (as T. suaveolens Engl.) and V. verdoorniana (Exell & Mendonça) Mziray (as T. verdoorniana Exell & Mendonça), from the Flora of West Tropical Africa area (Burkill 1997: 651–653). Research into the characterization and anti-microbial and anti-malarial applications of alkaloid and limonoid compounds in Vepris is active and ongoing. Cheplogoi & al. (2008) and Imbenzi & al. (2014) respectively listed 14 and 15 species of Vepris that have been studied for such compounds.

On 6 June 1951, Edwin Ujor of the Nigerian Forestry Service collected a specimen (Ujor FHI 30422) of a tree in what, even then, was one of the last remnants of submontane forest (800–2000 m alt.) in the Bamenda Highlands of Cameroon. The specimen was annotated by Ronald Keay as “Vepris sp. nov. female flowers and fruits needed”. Keay was the originator and director of the botanical inventory programme, then based at Forest Research Institute, Ibadan, Nigeria, which had resulted in the collections by Ujor and others in what was then the British Southern Cameroons, now Southwest and Northwest Regions of the Republic of Cameroon. Keay also revised the first volume of the second edition of the Flora of West Tropical Africa (1954–1972), which included Rutaceae (Keay 1958). At that time, the segregate genera Araliopsis, Diphasia, Oricia, Oriciopsis and Teclea were still recognized, Mziray's (1992) excellent work uniting them into a single genus Vepris not having been published. Keay did not know in which of the formerly recognized segregate genera to place Ujor's specimen: “Also in this part of the key comes a specimen (Ujor FHI 30422) recently received from Bali Ngemba F. R., B amenda, Br. Cam. The flowers (male) have 8 stamens, but fruit and female flowers are needed to determine the genus; it is perhaps a new species of Vepris Commers. ex A. Juss., a genus not otherwise represented in our area, […]” (Keay 1958).

Letouzey, in Flore du Cameroun (1963:117) confused this specimen with Toddaliopis ebolowensis Engl, (now Vepris ebolowensis (Engl.) Onana). That this was incorrect, and that the specimen was probably a new species, unusual in the genus and especially in Cameroon due to its opposite, rather than alternate leaves, was pointed out by Cheek in Harvey & al. (2004), where it was named as “Vepris sp. B” and illustrated. Letouzey's error was confirmed and emphasized by Onana and Chevillotte (2015) in their revision of Vepris in Cameroon. Since repeated targeted efforts from 2000–2004 to rediscover the Ujor species have failed (Cheek in Harvey & al. 2004) and since it may be extinct, in the present paper Ujor's specimen is formally described as V. bali Cheek sp. nov. It is hoped that naming this species will relaunch efforts to rediscover and protect this species from extinction.

The number of flowering plant species known to science is disputed (Nic Lughadha & al. 2017), but a reasonable estimate is 369000 (Nic Lughadha & al. 2016), while about 2000 species are described as new to science each year (Kew 2016).

About 5 % of plant species have been assessed for their global extinction risk following the IUCN (2012) categories and criteria. This number rises to 21–26% when evidence-based assessments beyond those on IUCNs global list are taken into account, and 30–44% of these assessments consider the species assessed to be threatened (Bachman & al. 2018). Newly discovered species, such as that reported in this paper, are increasingly likely to be threatened, because widespread species tend to be discovered sooner [although there are notable exceptions to this rule, e.g. Cheek & Etuge (2009a)]. Generally, it is the more localized, rarer species that remain undiscovered. This makes it a priority to discover, document and protect such species before they become globally extinct, as is Oxygyne triandra Schltr. (Cheek & Onana 2011; Cheek & al. 2018). Most such Cameroonian species threatened with extinction are in that situation as a result of habitat clearance, mainly for smallholder and plantation agriculture following logging (Onana & Cheek 2011). Efforts are now being made to delimit the highest priority areas in Cameroon for plant conservation as Tropical Important Plant Areas (TIPAs) using the revised IPA criteria set out in Darbyshire & al. (2017). This is intended to help avoid the global extinction (where it is not already too late) of more narrowly endemic species such as Vepris bali.

Material and methods

This study is based on herbarium specimens. All specimens cited have been seen by the authors, unless indicated otherwise (“n.v.”). Herbarium citations follow Index Herbariorum (Thiers & al. 2018+), nomenclature Turland & al. (2018) and author citations IPNI (2018+). Material of the suspected new species was compared morphologically with material of all other African Vepris, principally at K, but also using material from BM, P and YA. The methodology used for the surveys in the cloud forest areas of Western Cameroon referred to are given in Cheek & Cable (1997). The conservation assessment was made using the categories and criteria of IUCN (2012). Herbarium material was examined with a Leica Wild M8 dissecting binocular microscope fitted with an eyepiece graticule measuring in units of 0.025 mm at maximum magnification. The drawing was made with the same equipment using a Leica 308700 camera lucida attachment.

Results and Discussion

The characters separating Vepris bali from V. ebolowensis are given in Table 1.

The affinities of Vepris bali may lie with the other submontane and montane Vepris of Cameroon, all of which also occur above 1500 m alt, and are trees with trunks of a diameter of 20 cm or more at 1.5 m above the ground. Table 2 gives diagnostic characters separating these species.

Table 1.

Characters distinguishing Vepris ebolowensis and V. bali.

Table 2.

Characters distinguishing the submontane tree species of Vepris of Cameroon. Data from Onana & Chevillotte (2015) except for V. bali.

In Onana & Chevillotte (2015), the Ujor specimen keys out as Vepris heterophylla. In fact Mziray (1992), in his excellent revision of generic limits of Vepris and related genera, cited the Ujor specimen as V. cf. heterophylla. However, V. heterophylla is a shrub of Guinean woodland in W Africa ranging from Mali to Cameroon, with the leaves alternate, the leaflet length : width ratio c. 3 : 1, the width of the median leaflets of the flowering stems 2–2.5(–3) cm, and both surfaces showing gland dots, whereas V. bali is a tree of submontane forest with opposite leaves, the leaflet length : width ratio c. 2 : 1, the width of the median leaflets of the flowering stems 4.1–5.2 cm, and both surfaces lacking gland dots.

Vepris bali Cheek, sp. nov. – Fig. 1.

Holotype: Cameroon, Northwest Region, “Bamenda District, Bali-Ngemba Forest Reserve, in high forest on upper line ‘B’ in enumeration block at the height of 5,700 ft (=1700m. alt.) with Uapaca sp., Garcinia sp., and Aningeria”, male fl., Mar 1951, Ujor FHI 30422 (K; isotype: FHI n.v.).

Diagnosis — Differing from Vepris ebolowensis (Engl.) Onana in being a submontane tree, with a trunk c. 28 cm in diam, at 1.5 m from ground, leaves opposite, and median petiolules 9–14 mm long (whereas V. ebolowensis is a shrub of lowland forest, with leaves alternate, and median petiolules c. 0 mm long).

Description —Tree, dioecious (probably); trunk c. 28 cm in diam, at 1.5 m from ground (“3ft. girth”), slash (underbark and sapwood of trunk, exposed by machete cut) “white-grey”. Leafy stems terete, 2.2–3.5 mm in diam., internodes 3–5 cm long, grey-brown, with longitudinal, winged ridges and lines of raised, white, narrowly elliptic lenticels 0.9–1.5 × 0.2–0.4 mm, epidermal surface minutely patent puberulent, hairs simple, 0.05–0.1 mm long. Leaves opposite (or slightly subopposite), trifoliolate; petiole terete, 2–2.8 × 0.1–0.15 mm, glabrous; leaflets subequal; lateral leaflets elliptic, 6–10.5 × 2.8–4.7 cm, c. ½ length and width of obovate median leaflet; median leaflet 10–12.6 × 4.1–5.2 cm, base acute, slightly decurrent into canaliculate, laterally flattened petiolule, acumen 1–3.5 mm long, apex minutely bifid or entire; lateral nerves (6–)8–11 on each side of midrib, arising at c. 70° from midrib and looping toward margin and linking to nerve above (brochidodromous); intersecondary nerves parallel, unbranched or branching only at apex, oil glands 0.15–0.2 mm in diam., c. 180 per cm², appearing colourless in transmitted light, not visible on either surface, both surfaces of leaf blade glabrous; petiolules 9–14 mm long. Inflorescence (male) terminal, indumentum as stem, extending to calyces, branches 4 from base, racemose, c. 5 cm long (except largest: paniculate, c. 10 cm long), c. 50-flowered; peduncle c. 1.5 cm long, internodes 1–2.5 cm long; partial-inflorescences opposite or subopposite, to 3.5 cm long, 2–15-flowered; bracts caducous or absent on main axis, bracts of partialinflorescences opposite, boat-shaped to narrowly triangular, c. 1.5 mm long, subtending shorter, flattened bracteoles. Pedicels 1.5–2.8 × c. 0.7 mm, surface with scattered oil glands. Calyx tube c. 0.6 × 2.5 mm; lobes 4, triangular c. 0.7 × 0.8 mm, margin densely pectinate-hairy. Petals 4, free, ovate to obovate-elliptic, c. 3.5 × 1.5–2 mm, slightly concave, glabrous, oil glands 15–20, visible on both surfaces, apex rounded to obtuse. Stamens 8, equal in length to petals, erect; filament dorsiventrally flattened, 2.6–3 × c. 0.3 mm; anther ovate-oblong, c. 1 × 0.5 mm, medifixed. Gynoecium 2-loculed, depressed ovoid, c. 1.5 × 1.8 mm, surface densely covered in straight, black, bristle-like hairs c. 0.5 mm long, apex retuse, sinus c. 0.5 mm deep. Female flowers, fruits and seeds unknown.

Fig. 1.

Vepris bali-A: habit, flowering stem with male inflorescence; B: stem detail showing indumentum and lenticels; C: abaxial leaf surface showing oil glands; D: portion of partial-inflorescence showing bracts; E: male flower, side view; F: male flower, 2 sepals and petals removed and staminal filaments truncated; G: cross-section of rudimentary pistil. - Drawn from the holotype, Ujor FHI 30422 (K), by Hazel Wilks.

Fig. 2.

Global distribution of Vepris bali (marked in red).

Distribution — Cameroon, Northwest Region, Bamenda Highlands, Bali Ngemba Forest Reserve (Fig. 2).

Ecology — Submontane (cloud) forest with Aningeria, Garcinia and Uapaca, altitude c. 1500 m.

Conservation status — Despite targeted searching for this species by numerous botanical teams during surveys for months, over multiple seasons from 2000–2004, “Vepris sp. B” was not rediscovered (Harvey & al. 2004: 32) and has not been found subsequently (Onana & Cheek 2011). The higher altitudinal zones from which Ujor collected the type have seen clearance for agriculture by the inhabitants of villages such as Pinyin situated above the forest reserve. It is possible that V. bali is already extinct. It has not been found in other patches of submontane forest in the Cameroon Highlands, such as Mt Cameroon (Cable & Cheek 1998), Mt Oku and the Ijim Ridge (Cheek & al. 2000), Mt Kupe and the Bakossi Mts (Cheek & al. 2004), the Lebialem Highlands (Harvey et al. 2010), nor in the forest of Dom (Cheek & al. 2010).

However, it may yet be refound, as was Ternstroemia cameroonensis Cheek, previously also thought to be probably extinct (Cheek & Onana 2011; Cheek & al. 2017). If so, public education, safeguarding live trees, seed collection and banking, development of propagation protocols, and multiplication for reintroduction to safe sites are all strongly urged to help ensure the survival of Vepris bali.

Because “Vepris sp. B” was not formally published with a species name it has not previously been formally assessed for its conservation status using the IUCN standards. It was anticipated that when published it would be recognized as a threatened species (Cheek in Onana and Cheek 2011: 309).

Here Vepris bali is assessed as Critically Endangered using the IUCN (2012) categories and criteria. Under Criterion B, it is assessed as CR B2ab(iii) in view of the threats stated above, and because there is a single location, with an area of occupancy of 4 km² using the grid cells of that size as preferred by IUCN. Under Criterion D, is merits the same level of threat because fewer than 50 mature individuals are known. In fact, only a single individual has been recorded, despite targeted searching over several years. The reality is that V. bali may already be extinct.

Local names and uses — None recorded.

Etymology — The specific epithet is a noun in apposition, from the town and people of Bali in the B amenda Highlands of the Northwest Region of Cameroon, near which, in the Bali Ngemba Forest Reserve, the only known locality for this tree is found.

Remarks — The only other opposite-leaved Vepris in W and C Africa is V. felicis Breteler of Guinea to Ivory Coast, a Critically Endangered (Cheek 2017a) lowland 1–2 m tall shrub species with unifoliolate leaves, which is therefore unlikely to be confused with V. bali.

The discovery of such a distinctive new species in Bali Ngemba, one of the remnant cloud forest areas of the Cameroon Highlands, is not unusual. Among more than one hundred other remarkable and usually globally threatened species discovered in these cloud forests have been: Coffea montekupensis Stoff. (Stoffelen & al. 1997), the world's only pink-flowered coffee; Coleochloa domensis Muasya & D. A. Simpson (Muasya & al. 2010), the only uniquely epiphytically dwelling sedge globally; Impatiens etindensis Cheek & Eb. Fischer (Cheek & Eb. Fischer 1999), the only tuberous epiphytic impatiens W of the Albertine rift; Kupea martinetugei Cheek & S. A. Williams (Cheek & al. 2003), a new genus of achlorophyllous mycotroph representing a new tribe of Triuridaceae, sister to the rest of the family; and Ledermanniella pollardiana Cheek & Ameka (Cheek & Ameka 2008), an unusual Podostemaceae.

These cases illustrate the scale at which new discoveries are being made in the highlands of Western Cameroon. These highlands include several Pleistocene refugia and occur in the most species-diverse degree squares documented in tropical Africa (Cheek & al. 2001).

Most of the species listed above are threatened with extinction, because they are narrow endemics with small ranges, restricted to mainly submontane (cloud) forest patches, which are steadily being cleared, mainly for small-scale cultivation of food crops. These species feature in the Red Data Book of Cameroon (Onana & Cheek 2011).