Talbotiella couteronii Sonké, M. Simo & Burgt, 2024

Sonké, Bonaventure, Simo-Droissart, Murielle, Bidault, Ehoarn, Ngoula, Fernandez & van der Burgt, Xander M, 2024, Talbotiella couteronii (Leguminosae: Detarioideae), a new gregarious tree species from Cameroon, Plant Ecology and Evolution 157 (3), pp. 407-416 : 407-416

Talbotiella couteronii Sonké, M. Simo & Burgt sp. nov.

Figs 1 , 2 , 3 , 4 , 5 , Table 1

Type.

CAMEROON – Central Region • Mbébé (Silobé); 4°07’45.5”N, 11°00’11.6”E; 19 Mar. 2024; fl.; Sonké & Ngoula 7886; holotype: BRLU; isotypes: BR, BRLU, E, K, M, MA, MO, P, WAG, YA .

Diagnosis.

This species closely resembles T. batesii , from which it differs by the number of bud scales (11–17 vs 3–5), narrower stipules (9–15 × 1–1.5 mm vs 13–15 × 2–2.5 mm) that are glabrous on both surfaces (vs pubescent outside along the midrib), usually fewer leaflets (( 5 –) 6–9 (– 10) pairs vs 9–13 pairs), looser inflorescence with longer pedicels (10–20 mm vs 3–8.5 mm) and usually fewer flowers (5–12 vs 10–18), larger ovary (4–6 × 2–3 mm vs 1.5–3.5 × 1–1.3 mm), and larger seeds (14–21 × 10–15 × 2–3 mm vs 9–10 × 9–10 × 2–3 mm).

Description.

Small to medium-sized tree 5–25 m, dbh 6–60 cm; slightly fluted trunk, with slight buttresses; bark smooth on younger individuals, peeling off in small longitudinal patches, grey-brown (Fig. 3 ). Twigs sparsely to moderately pubescent, hairs ca 0.5 mm long; mature twigs glabrescent. Bud scales 11–17, caducous, distichous, brown, coriaceous, not keeled, outer and inner surface glabrous; proximal scale orbicular, ca 1.5 mm diam.; distal scales becoming progressively longer and relatively narrower, apical scale obovate, ca 7– 4 mm. Stipules rapidly deciduous (seen in young foliage, Sonké & Ngoula 7895, Fig. 4 C ) in pairs, free, auriculate at base; the auricle to 1 × 1 mm; upper part of stipule narrowly lanceolate to spathulate; 9–15 × 1–1.5 mm; glabrous on both surfaces, edge ciliate. Leaves alternate, paripinnate, 5.2–8 (– 9) × 2.2–4 cm; petiole 1–3 mm long, leaf rachis 3–6 cm long, canaliculate, shortly hairy to glabrescent; leaflets sessile, narrowly oblong, in (5 –) 6–9 (– 10) pairs, opposite, the lowest ones subopposite, 13–23 × 5–8 (– 9) mm; base asymmetric, proximal margin tapering towards apex, glabrous above, lower surface appearing glabrous with a hand lens but sparsely appressed puberulous under a microscope; fringing hairs present particularly on the lower margins of young leaflets but absent in mature foliage; midvein central, prominent above and below for most of its length; glands 0–3, present on the distal half of the lower surface near the petiolule, positioned about midway between midvein and margin. Inflorescence a 5–12 - flowered axillary raceme; peduncle and rachis together 2.5–4 cm long, light green, with a dense indumentum of golden patent hairs up to 1 mm long; bud scales 8–12, caducous, distichous, brown, coriaceous, not keeled, outer and inner surface glabrous; proximal scale orbicular, ca 1.5 mm diam.; distal scales becoming progressively longer and relatively narrower; apical scale obovate, 8 × 5 mm, leafy, not keeled, pubescent along midrib, pale green; floral bracts obovate to spathulate, 7–9 × 1–2 mm, pale green, densely hairy outside and sparsely so inside, margin ciliate; pedicels white to pink, 10–20 mm long, sparsely pubescent, hairs up to 0.5 mm long; bracteoles caducous, inserted on the pedicel just above the middle, opposite or sub-opposite, linear to narrowly oblong, 4–7 × 0.3–0.5 mm, tapering towards the apex, white, glabrous or with a few scattered hairs outside. Hypanthium narrowly campanulate, white, 1–1.5 mm long, glabrous, inner surface glabrous. Sepals 4, obovate, white, cucullate, glabrous, 5–6 × 2–4 mm. Petals absent. Stamens 10; filaments free, 8–13 mm long, white, glabrous; anthers oblong-elliptic, ca 2 mm long, orange. Ovary oblong, 4–6 × 2–3 mm, pale pink, densely pubescent with white hairs up to 1 mm long that become golden when dry, on stipe ca 1 mm long; partly fused to the adaxial side of the hypanthium up to ca 2 mm; ovules 2–3; style 6–8 mm long, reddish at the base and greenish white towards the top, with a few long hairs in the lower third, otherwise glabrous, stigma capitate, pale yellow. Pod flattened (Fig. 4 D ), 3.3–6.4 × 1.5–3.3 cm, obovate-triangular, upper suture slightly broadened, 3–4 mm wide (both valves included), surfaces and suture moderately golden puberulous, beak 5–6 mm long. Seeds discoid, 1–2 per fruit, 14–21 × 10–15 × 2–3 mm; testa deep reddish brown (Sonké & Ngoula 7889, Fig. 4 E ).

Distribution and chorology.

Talbotiella couteronii is currently known only from Cameroon. It is an endemic of the middle Sanaga basin (Fig. 1 ). Lower Guinea Domain of the Guineo-Congolian Region.

Habitat and ecology.

Riverine forest on the banks of the Sanaga River, on sandy soils with a shallow water table, with tree heights ranging from 15 to 20 m. Other tree species include Albizia adianthifolia W. Wight , Macaranga spinosa Müll. Arg. , Myrianthus arboreus P. Beauv. , and Lindackeria dentata Gilg. The undergrowth is relatively open, composed mainly of herbaceous plants of the genus Thunbergia Retz. , and shrubs of the genera Psychotria L. and Rinorea Aubl. The riverine forest along the Sanaga River may be flooded during the rainy season, without the water remaining for very long. This forest is located at 320–420 m a. s. l. Talbotiella couteronii is a gregarious species (Fig. 5 ); the species may occur almost monodominant.

Phenology.

Talbotiella couteronii flowers and leaf flushes in March, at the start of the rainy season. All the flowers in an inflorescence open at almost the same time (Fig. 4 B ). In April, fruits are maturing and seeds are dispersed (Fig. 4 D – E ).

Etymology.

This new species is named after Dr Pierre Couteron (Institut de Recherche pour le Développement, Montpellier, France) in recognition for his constant support to the first author.

Preliminary IUCN conservation assessment.

Talbotiella couteronii is known from 28 collections representing 26 unique occurrences and two or three subpopulations. Its extent of occurrence (EOO) is calculated as 288 km 2, whereas its area of occupancy (AOO) is estimated as 44 km 2, both fall within the limits for the Endangered category under criterion B. Eight occurrences located downstream of the Kikot hydroelectric dam project are threatened by shifting agriculture (one location) and are not expected to be threatened by the dam project (not a regulating dam). Nine occurrences are located in the future hydroelectric dam reservoir at Kikot, while one occurrence is on the future construction site of the dam itself; these ten occurrences are threatened by the hydroelectric dam project whose implementation will lead to their disappearance; they all represent one location. One occurrence located on the site of the proposed Binoum quarry will also disappear; it represents one location, different from the location associated with the dam itself, as the threat is of different nature. We did not identify any threat to seven occurrences located upstream from the dam project, including six at Ntol-Lébanga and one at Badissa; these seven occurrences represent two locations. With regard to the most serious plausible threats, which are the Kikot hydroelectric dam construction project and the Binoum quarry, the 26 occurrences represent five locations, which is at the upper limit of the Endangered category according to criterion B. We believe that the various threats have led to and will continue to lead to the decline in the habitat quality of this species. In addition, the disappearance of occurrences at the dam construction site, its reservoir and the Binoum quarry site will lead to a continued decline in EOO, AOO, the number of locations, and the number of mature individuals of the species. For all these reasons, Talbotiella couteronii is assessed as Endangered: EN B 1 ab (i, ii, iii, iv, v) + B 2 ab (i, ii, iii, iv, v).

Additional material examined.

CAMEROON • Kikot, en aval du grand pont sur la Sanaga ; 4°10’11.5”N, 11°0’57”E; 11 Oct. 2022; Nzoyeuem D 136; BRLU, YA • Tombi ; 4°09’48.7”N, 11°01’17.9”E; 18 Mar. 2022; Tcheferi 42; BRLU, YA • Badissa , 4°38’47.9”N, 11°22’25.2”E; 23 Jan. 2024; Relevé, Cameroun 353; BRLU, YA • Kikot , 4°10’34.4”N, 11°01’26.1”E; 1 Aug. 2022; Sonké & Ngoula 7035; BRLU, MO, YA • Kikot, île principale ; 4°10’39.4”N, 11°01’38.4”E; 5 Apr. 2023; Sonké & Simo 7327; BR, BRLU, K, M, MO, P, YA • Nkolmelen ; 4°14’03.8”N, 11°08’16.1”E; 5 Jul. 2023; Sonké & Simo 7462; BR, BRLU, MO, YA • Nkolmelen ; 4°15’29.4”N, 11°06’47.2”E; 30 Jul. 2023; Sonké 7483; BR, BRLU, MO, P, YA • Nkolmelen ; 4°14’26.9”N, 11°07’21.4”E; 31 Jul. 2023; Sonké 7488; BR, BRLU, MO, P, YA • Nkolmelen ; 4°14’23.9”N, 11°07’16.4”E; 1 Aug. 2023; Sonké 7502; BR, BRLU, MO, YA • Nkolmelen ; 4°14’19.1”N, 11°07’04.3”E; 1 Aug. 2023; Sonké 7505; BRLU, MO, YA • Mbébé ; 4°09’12.6”N, 11°00’46.2”E; 19 Aug. 2023; Sonké & Simo 7535; BR, BRLU, MO, P, YA • Mbébé ; 4°09’12.6”N, 11°00’46.2”E; 22 Aug. 2023; Sonké & Simo 7578; BR, BRLU, K, M, MO, P, WAG, YA • Mbébé (Silobé); 4°07’42.1”N, 11°00’05.1”E; 19 Mar. 2024; Sonké & Ngoula 7884; BR, BRLU, K, M, MO, P, YA • Mbébé (Silobé); 4°07’42.3”N, 11°00’06.6”E; 19 Mar. 2024; Sonké & Ngoula 7885; BR, BRLU, K, M, MO, P, YA • Same data as for preceding; 29 Apr. 2024; Sonké & Ngoula 7889; BR, BRLU, K, M, MO, P, YA • Île principale , Kikot; 4°10’04.2”N, 11°01’02.0”E; 19 Mar. 2024; Sonké & Ngoula 7887; BR, BRLU, K, M, MO, P, YA • Île principale , Kikot; 4°10’03.8”N, 11°01’00.9”E; 19 Mar. 2024; Sonké & Ngoula 7888; BR, BRLU, K, M, MO, P, YA • Same data as for preceding; 29 Apr. 2024; Sonké & Ngoula 7891; BR, BRLU, K, M, MO, P, YA • Mbébé (Silobé); 4°07’45”N, 11°00’12”E; 29 Apr. 2024; Sonké & Ngoula 7890; BR, BRLU, K, M, MO, P, YA • Île principale , Kikot; 4°10’04.0”N, 11°01’01.9”E; 29 Apr. 2024; Sonké & Ngoula 7893; BR, BRLU, K, M, MO, P, YA • Île principale , Kikot; 4°10’13.8”N, 11°01’27.7”E; 29 Apr. 2024; Sonké & Ngoula 7894; BR, BRLU, K, M, MO, P, YA • Île principale , Kikot; 4°10’15.4”N, 11°01’32.2”E; 29 Apr. 2024; Sonké & Ngoula 7895; BR, BRLU, K, M, MO, P, YA • Île principale , Kikot; 4°10’09”N, 11°01’20.2”E; 29 Jan. 2022; Transect, Cameroun 248; BRLU, YA • Kikot ; 4°09’46.2”N, 11°00’04.46”E; 21 Apr. 2022; Transect, Cameroun 472; BRLU, YA • Ntol-Lébanga ( île de Ponis ); 4°14’26.5”N, 11°07’20.3”E; 30 Jul. 2023; Transect, Cameroun 825; BRLU, YA • Mbébé , 4°07’42.2”N, 11°00’4.7”E; 21 Aug. 2023; Transect, Cameroun 933; BRLU, YA • Ntol-Lébanga, en amont du site du projet de construction du barrage de Kikot ; 4°14’17.9”N, 11°07’13.6”E; 12 Jan. 2024; Relevé, Cameroun 146; BRLU, YA .

Notes.

The specimens Sonké & Ngoula 7885 and 7889 were collected from the same tree. Similarly, Sonké & Ngoula 7888 and 7891 were collected from the same tree.

Figures

Figure 1. Distribution of Talbotiella couteronii and T. bakossiensis in Cameroon.

Figure 2. Talbotiella couteronii. A. Flowering branch. B. Infructescence with two pods; two seeds. C. Flower with a single bract, two bracteoles, four sepals and 10 stamens. D. Stipule. E. Leaflet lower side, with two glands. F. Leaf upper side, with nine pairs of leaflets. A, E, F drawn from Sonké & Ngoula 7886 (K); B from Sonké & Ngoula 7889 (K); C from Sonké & Ngoula 7887 (K); D from Sonké & Ngoula 7888 (K). Drawing by Xander van der Burgt.

Figure 3. Talbotiella couteronii. A. Trunk in low-angle view. B. Base of trunk showing bark detachment in patches. Photographed at Île principale, Kikot by Bonaventure Sonké.

Figure 4. Talbotiella couteronii. A. Opened flowers. B. Twig with inflorescences. C. Young leaves with stipules. D. Infructescence with two fruits. E. Immature fruits and five unripe seeds. A from Sonké & Ngoula 7888; B from Sonké & Ngoula 7886; C from Sonké & Ngoula 7895; D, E from Sonké & Ngoula 7889.

Figure 5. A forest dominated by Talbotiella couteronii. Photographed at Nkolmelen, Île de Ponis by Bonaventure Sonké.