Introduction

It came as a great surprise to discover a new tree species of Talbotiella Baker. f. in Guinea. One of the localities of the new species (Burgt 2188) is situated at only 46 km northeast of the centre of the capital Conakry and 6 km northeast of the town centre of Coyah, part of the Conakry urban agglomeration. The new species is located 1400 km further west from the distribution area of Talbotiella gentii Hutch. & Greenway in Ghana, the westernmost of the eight previously known Talbotiella species (Mackinder et al. 2010b). The new species is found in and near Coyah Préfecture where it occurs gregariously in forested valleys of a sandstone plateau. Although it is very common in some of these valleys, it had never before been collected, perhaps because collectors were focussing on areas further inland, in the Fouta Djalon, where more interesting plant collecting opportunities were thought to exist. The short flowering period may also have contributed to the new species remaining unnoticed for so long. This, however, changed when Martin Cheek, head of the Africa and Madagascar Team of the Identification and Naming Department of the Royal Botanic Gardens, Kew, turned his attention to the last remaining forest patches in the valleys on the sandstone plateau of the Coyah Préfecture. In September 2015, he collected the first specimens of the new species.

The genus Talbotiella was revised by Mackinder et al. (2010b). Eight species were recognised, of which four were newly described and one was transferred from Hymenostegia Harms. Seven species are relatively rare trees, occurring in small areas. The eighth species occurs in a larger area but is known from only seven collections. Six species were assessed as critically endangered (CR) and two as endangered (EN). Together, the eight Talbotiella species treated by Mackinder et al. (2010b) occur in Ghana, Nigeria, Cameroon, Gabon and Congo (Brazzaville). In Cameroon, the centre of diversity of the genus, six of the eight species occur, five of which are country endemics (Mackinder et al. 2010b).

The genus Talbotiella is placed in the Leguminosae subfamily Detarioideae (LPWG 2017). The genus is characterised by the unique combination of the presence of imbricate bud scales, persistent petaloid bracteoles, the absence of petals and a pubescent ovary (Mackinder et al. 2010b). The species of the closely related genus Hymenostegia are characterised by the presence of two or three well developed spathulate petals providing a clear distinction from Talbotiella species (Mackinder et al. 2010a). The species of another closely related genus, Plagiosiphon Harms, usually have five well-developed petals, three large and two smaller (Aubréville 1970). The new species is placed in the genus Talbotiella, because it has the combination of morphological characters mentioned for the genus, including an absence of petals on the four known flowering collections.

Talbotiella cheekii Burgt sp. nov. Type: Guinea, Coyah Préfecture, along stream between villages Saliya and Yataraya, 7 April 2017, X. M. van der Burgt, P. M. Haba, A. Diallo & G. Konomou 2084 (holotype K [K001244000], isotypes B, BM, BR, C, E, EA, ETH, F, FHO, FI, G, GH, H, HBG, HNG, LBV, LE, LISC, MA, MO, MPU, NY, O, P, PRE, S, SING, US, W, WAG, YA).

http://www.ipni.org/urn:lsid:ipni.org:names:77179007-1

Tree to 21 m high, stem diam. to 83 cm; bole 0.5 – 7 m long, straight, cylindrical or fluted, sometimes with buttresses to 1.5 m high and 1 m wide; bark light brown with sparse thin flakes; larger branches nearly vertical. Stems densely hairy to glabrescent, hairs to 0.3 mm long. Bud scales of leafy twigs and inflorescences identical, up to 12, distichous, imbricate, caducous, coriaceous, not keeled, outer surface hairy around midrib, margins ciliate, inner surface glabrous; proximal scale suborbicular, 1 × 2 mm, distal scales becoming progressively larger and more papery, apical scale obovate, to 22 × 6 mm. Stipules (seen on young foliage) in pairs, free, narrowly lanceolate, 6 – 26 × 1 – 2 mm, apex acute, sometimes auriculate at base, auricle 1 × 0.5 mm, outer surface and margins hairy, hairs to 1 mm long, inner surface glabrous. Leaves paripinnate, 5 – 9 × 2.5 – 4 cm; petiole 1.5 – 3 mm long, leaf rachis 4 – 7 cm long, densely hairy, hairs to 0.5 mm long. Leaflets sessile, in 9 – 14 pairs per leaf, upper and middle leaflets opposite, lower pairs sub-opposite, largest leaflets on fertile branches 12 – 22 × 4 – 7 mm, 2.9 – 3.4 × longer than wide, smallest leaflets 8 × 3 mm; leaflets oblong, base and apex asymmetric, apex rounded to slightly emarginate; mature leaflets glabrous on both sides, midvein of young leaflets hairy above, margin sparsely ciliate, lower surface sparsely appressed hairy; midvein running in middle of leaflet; venation above obscure, below clear; 0 – 2 glands on the distal half of the lower surface, near the rachis. Inflorescence a 10 – 18-flowered raceme, axis 3 – 6 cm long including a peduncle about 1 cm long, peduncle and rachis densely hairy, hairs to 1 mm long; floral bract white, linear, 9 – 17 × 1 – 1.5 mm (to 4 mm wide on the lowest flower of an inflorescence), edges and veins on outer surface hairy, hairs to 0.6 (– 1) mm long, inner surface glabrous. Flowers: pedicel pink to red, sparsely hairy, hairs to 0.5 (– 1.2) mm long, portion of pedicel below bracteoles 6 – 18 mm long, portion above bracteoles 3 – 6 mm long. Bracteoles white, (sub-) opposite, linear, 8 – 18 × 0.7 – 1.6 mm, glabrous, a single trichome to 0.6 mm long at apex; hypanthium pink to red, campanulate, 2 – 3 mm long, longest on the adaxial side, 1.5 – 2 mm wide at top, sparse hairy, upper part often glabrous. Sepals 4, white, ovate, cucullate, glabrous, a few hairs at apex, apex rounded, the apex of all 4 sepals may be bilobed, 5 – 8 × 3 – 5 mm, abaxial and adaxial sepals wider than lateral sepals. Petals absent. Stamens 10, filaments white, free, 7 – 13 mm long, glabrous; anthers orange-brown, elliptic, 1.2 – 1.4 mm long. Ovary reddish green to dark red, 3 – 6 × 1.5 – 2 mm, glabrous, the margin densely hairy, hairs to 0.5 mm long; stipe 2 mm long, mostly fused to the adaxial side of the hypanthium, ovules 2, style white to pink, 6 – 8 mm long, sparse hairs on lower part, upper part glabrous, stigma capitate. Infructescence axis 3 – 6 cm long, densely hairy, hairs to 1 mm long, with up to 5 pods, fruiting pedicels 1.4 – 2.1 cm long, sparsely hairy, hairs to 0.5 mm long. Pod 1 – 2-seeded, 4.5 – 7.7 × 2 – 3.6 cm, stipe 2 mm long, beak acuminate, 2 mm long, upper suture slightly broadened, pod surface glabrous, both sutures with sparse hairs 0.5 mm long. Seeds brown, disk-shaped, 15 – 17 × 14 – 16 × 4 mm. Seedling hypocotyl 5 – 8 cm, epicotyl 5 – 8 cm, two opposite leaves 6 – 8 × 3 – 4 cm, each with 7 – 9 pairs of leaflets, largest leaflets 15 – 23 × 6 – 8 mm. Figs 1 – 3.

Fig. 1
figure 1

Talbotiella cheekii. A two flowers; B twig with inflorescences; C infructescence with two fruits; D leaves. A – B from Burgt 2087; C from Molmou 988; D from Burgt 2065. photos: a, b, d xander van der burgt; c martin cheek.

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recognition

Talbotiella cheekii is morphologically similar to T. batesii Baker f. The pedicels of T. cheekii are pink to red, 9 – 24 mm long; the bracteoles are 8 – 15 × 0.7 – 1.5 mm (the pedicels of T. batesii are white, 4 – 10.5 mm long; the bracteoles are 6 – 8.5 × 1.1 – 2.5 mm). The ovary of T. cheekii is reddish green to dark red, and glabrous with only the edges densely hairy (the ovary of T. batesii is pale pink, and densely hairy). The pod of T. cheekii is glabrous, the sutures sparsely hairy (the pod of T. batesii has the surfaces and suture moderately puberulous). The leaflet apex of T. cheekii is rounded to slightly emarginate (the leaflet apex of T. batesii is acute).

DISTRIBUTION

Guinea (Map 1). Talbotiella cheekii occurs on the sandstone plateau in the northern part of Coyah Préfecture. Its distribution just extends into Dubreka and Kindia Préfectures.

Map 1
figure 2

Distribution of Talbotiella cheekii Burgt sp. nov. in West Africa

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specimens examined . guinea

Coyah Préfecture, valley in sandstone plateau SE of Kouriya, 9°45'29.1"N, 13°18'06.0"W, 350 m, sterile, 11 Oct. 2016, Burgt 2065 (BR, G, HNG, K, MO, P, PRE, WAG); valley in sandstone plateau E of Kouriya, 9°46'41.6"N, 13°16'42.0"W, 260 m, seedlings, 12 Oct. 2016, Burgt 2068 (BR, HNG, K, MO, P, WAG); along stream between villages Saliya and Yataraya, 9°45'23.7"N, 13°15'41.4"W, 120 m, fl., 7 April 2017, Burgt 2084 (holotype K; isotypes B, BM, BR, C, E, EA, ETH, F, FI, FHO, G, GH, H, HBG, HNG, LBV, LE, LISC, MA, MO, MPU, NY, O, P, PRE, S, SING, US, W, WAG, YA); along small stream SW of Kaporo Village, 9°43'01.6"N, 13°16'51.1"W, 130 m, fl., 8 April 2017, Burgt 2087 (B, BR, G, HNG, K, LISC, MO, NY, P, PRE, SING, WAG); on hill slope just E of Sagouya Village, 9°42'38.8"N, 13°16'47.4"W, 190 m, fl., 10 April 2017, Burgt 2093 (B, BR, G, HNG, K, LISC, MO, P, PRE, WAG); along rocky stream 3.5 km NE of Malassi Village, 9°41'33.4"N, 13°13'42.2"W, 110 m, old inflor., 13 April 2017, Burgt 2097 (B, BR, G, HNG, K, LISC, MO, P, PRE, WAG); Kindia Préfecture, Plateau de Tassing above Fossikouré Village, 9°41'59.1"N, 13°10'41.7"W, 540 m, sterile, 8 Dec. 2017, Burgt 2187 (BR, HNG, K, MO, P, SERG, WAG); Coyah Préfecture, vertical sandstone cliff 50 m above stream at the checkpoint near Pont KK, 9°45'05.5"N, 13°21'27.6"W, 150 m, fl., 9 Dec. 2017, Burgt 2188 (B, BR, G, HNG, K, LISC, MO, P, PRE, SERG, WAG); Kakiwoundi Forest, 9°43'46"N, 13°17'28.2"W, 250 m, sterile, 28 Sept. 2015, Cheek 18133 (HNG, K, WAG); valley in sandstone plateau SE of Kouriya, 9°45'29"N, 13°18'16.7"W, 188 m, sterile, 28 Sept. 2015, Cheek 18190 (HNG, K); Dubreka Préfecture, plateau E of Dobiro Village, 9°50'37.5"N, 13°26'16.8"W, 420 m, sterile, 10 Dec. 2017, Haba 1095 (HNG, K, WAG); Coyah Préfecture, plateau S of Kouriya, 9°45'05.5"N, 13°20'28''W, 200 m, fr., 10 Sept. 2017, Konomou 294 (HNG, K, WAG); Kakiwoundi Forest, 9°43'45.9"N, 13°17'17.8"W, 220 m, fr., 8 June 2016, Molmou 988 (HNG, K, WAG).

HABITAT

Talbotiella cheekii occurs in closed-canopy semi-deciduous forest on rocky stream banks and rocky hill slopes, alt. 100 – 600 m. The general precipitation is about 2800 mm/y but may be higher or lower in the valleys where the trees are found, due to orographic influences on precipitation levels. The climate is strongly seasonal with a pronounced dry season from December to April. Talbotiella cheekii occurs gregariously, in Detarioideae-dominated forest. The species occurs with the four Detarioideae species Cryptosepalum tetraphyllum (Hook. f.) Benth., Guibourtia copallifera Benn., Gilbertiodendron aylmeri (Hutch. & Dalziel) J. Léonard and Tessmannia baikiaeoides Hutch. & Dalziel.

conservation status

There is not much forest left in Coyah Préfecture. Slash-and-burn farming, annual dry-season grass fires damaging forest edges, and urban development have much reduced the area under forest cover. Talbotiella cheekii was found in about twelve forest patches, between 1 and 7 ha in size, situated on steep rocky slopes or along rocky streams. Numerous seedlings, saplings and juvenile trees are present in these forest patches. Trees will not survive forest fires, although they may survive coppicing at about 1 m high which the local farmers often practice when they convert forest into farmland. The main stem of T. cheekii trees is usually too short and fluted to be useful as construction timber. Poles are made from juvenile trees with a straight trunk and used in the construction of houses. Several T. cheekii trees were observed broken where adjacent trees had been logged.

Talbotiella cheekii classifies as Endangered under IUCN (2017) criterion B1. The extent of occurrence is 166 km2, calculated with Geocat (2018) from the 13 cited specimens and 10 field observations. Additional forest patches exist in localities which, to date, are unvisited; both within and near the current extent of occurrence. The extent of occurrence may therefore increase because of future surveys but will almost certainly remain within the IUCN (2017) EN B1 thresholds of 100 – 5000 km2. The number of mature trees seen by the authors is estimated at 1600 – 2400. The total number of mature trees is estimated at 5000 – 10000. The twelve forest patches are located near seven different villages or suburbs; therefore, the species is supposed to occur in seven locations (IUCN 2017). However, there is a reduced probability of recolonisation; therefore T. cheekii may be considered severely fragmented and IUCN criterion B1a still indicates EN (IUCN 2017). Talbotiella cheekii trees are found in small and often relatively isolated subpopulations, most of which are located near farmland or near land divided up for urban development. Some of these small subpopulations may go extinct soon. The ballistic seed dispersal method of T. cheekii (see the notes section below) results in a relatively short (probably less than 30 m) and strictly limited maximum seed dispersal distance. Except for dispersal by water downstream in gullies and streams, long-distance seed dispersal methods are unknown for T. cheekii and related Detarioideae tree species (Burgt 1997; Burgt pers. obs.).

Talbotiella cheekii also classifies as Endangered under IUCN criterion A. The authors have seen several patches of farmland on rocky slopes and several galleries of secondary vegetation along rocky streams, where only a few damaged T. cheekii trees were present. Presumably there were once many more trees there, since T. cheekii always occurs gregariously in natural forests. If the generation length is roughly estimated to be 40 years, the reduction of forest cover in the region where T. cheekii occurs is estimated to have resulted in 60% to 90% population reduction of T. cheekii trees over the past three generations. In the future, the population reduction will likely continue but may become somewhat less, because some of the remaining trees were growing in places unsuitable for farming and relatively safe from forest fires: amongst large rocks along streams and on steep cliffs. However, if the current rate of deforestation in Coyah Préfecture continues, the population reduction of T. cheekii may well be over 50% during the next three generations.

Talbotiella cheekii is here assessed, following IUCN Red List categories, as Endangered, EN A2c+3c; B1ab(iii,iv,v) (IUCN 2017). Conservation actions are planned to protect the species. Martin Cheek is working with the Guinean Ministère de l’Environnement des Eaux et Forêts to increase protection of the region where T. cheekii occurs, as well as other regions with rare plant species. National and local authorities will be informed about the conservation importance of the species. Conservation posters will be prepared and distributed. The tree may be planted in gardens. Seeds will be collected for Kew’s Millennium Seed Bank; although it is not certain that the seeds are orthodox since they are dispersed at the height of the rainy season.

phenology

Talbotiella cheekii flowers and leaf flushes in April, at the end of the dry season. All flowers of an inflorescence open at the same time (Fig. 1B); the few flower buds present on Burgt 2084, the first of the flowering collections, were unable to open because they were insect infested. All mature trees of T. cheekii were flowering simultaneously on the 7th and 8th of April 2017. No observations were made on the 6th of April or before that date. On the 9th and 10th of April only wilted flowers were present. The flowering tree collected on 9th of December 2017, Burgt 2188, was badly damaged by fire and presumably therefore flowering, as there were no other trees flowering at that time.

In June and July fruits are mature and seeds are dispersed. The seeds germinate within a week after dispersal. All species of Talbotiella of which fruits are known, disperse their seeds ballistically (Mackinder et al. 2010b). The seeds of T. cheekii are also dispersed in this way, with the drying valves of a pod curling in opposite directions. Talbotiella cheekii trees are gregarious (Fig. 2B) and this tendency is probably related to the relatively short and strictly limited maximum dispersal distance of the ballistic seed dispersal within a forest environment.

Fig. 2
figure 3

Talbotiella cheekii. A crown of tree in flower; B group of trees; C stem of a young tree; D stem of an old tree. A from Burgt 2093; B – D not collected. photos: xander van der burgt.

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Fig. 3
figure 4

Talbotiella cheekii. A branch with inflorescences; B leaf upper surface; C infructescence with three fruits; D leaflet lower surface showing two glands; E stipule; F auriculate stipule; G flower. A, E, G from Burgt 2087; B, D, F from Burgt 2065; C from Molmou 988. drawn by xander van der burgt.

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etymology

Talbotiella cheekii is named after Dr Martin Cheek, Head of the Africa & Madagascar Team in the Identification and Naming Department of the Royal Botanic Gardens, Kew. The new species was discovered thanks to his long-standing commitment to the study of African plants. He has been studying the flora of Guinea on field expeditions since 2005, supported the restoration of the National Herbarium of Guinea, and described a new genus and four new species from the country (Cheek & Burgt 2010; Cheek & Haba 2016a, 2016b; Cheek & Williams 2016; Cheek et al. 2016). He is also involved in the designation of new protected areas in Guinea as part of Kew’s Tropical Important Plant Areas (TIPAs) Project (Darbyshire et al. 2017) and is supervising a Darwin Initiative-funded project on rare plant species conservation in the country.

vernacular name

Linsonyi (from Burgt 2084); Meni (from Molmou 988); Wonkifong wouri khorohoi (from Burgt 2097), translated as the “Tree with hard wood from Wonkifong”. This last name was proposed by the people of Malassi village when the trees were shown to them. All three names are in the Susu language.

uses

The wood is fine-grained, with a density of c. 900 kg m-3. A pole made from the wood can be used as a pestle to pound food in a mortar (from Burgt 2084). A decoction from the leaves is used to remove the magical powers from confessed sorcerers (from Molmou 988).

notes

Talbotiella cheekii is characterised by the long pedicels, pink to red in colour, the long and narrow bracteoles, the glabrous pod (only the margin sometimes has a few hairs) and the rounded to slightly emarginate leaflet apex. Apart from this, the leaves and leaflets of T. cheekii and T. batesii are more or less similar; both species have 9 – 14 pairs of leaflets per leaf. Of all previously described Talbotiella species, T. cheekii is morphologically most similar to T. batesii. This is remarkable, because T. batesii is the easternmost species of Talbotiella, occurring in southeast Cameroon, northeast Gabon and north Congo (Brazzaville), at 2900 to 3100 km distance from T. cheekii, the westernmost species. A molecular analysis might show, however, that T. cheekii is more closely related to a different species, for example to T. gentii from Ghana, geographically the nearest of the eight existing Talbotiella species.

Two more plant species from the Leguminosae family have been newly discovered in Guinea in recent years: Eriosema triformum Burgt (Burgt et al. 2012), a pyrophytic herb with unifoliolate leaves, from submontane grassland, endemic to the Pic de Fon area in the Simandou Range, and Gilbertiodendron tonkolili Burgt & Estrella (Estrella et al. 2012), a tree from well-drained sandy and/or rocky soils on river banks and forest patches, first discovered in Sierra Leone, and later found to occur also in Guinea (e.g. the specimens Cheek 16172, 16583 and 16614; all in HNG and K).