Phragmanthera bidaultii Libalah & O. Lachenaud sp. nov.

Figs 1, 2, 3, 4, Table 1

Type

CAMEROON – Centre Region • Nkolmelen, Île de Mibanga; 4°14’13.27”N, 11°08’38.3”E; 1 Jul. 2023; fl., fr.; Sonké & Simo 7412; holotype: MO; isotypes: BR, BRLU, FR, K, M, MO, P, WAG, YA.

Diagnosis

Phragmanthera bidaultii has patent to reflexed corolla lobes, a style with a distinct neck under the stigma and stamen filaments without an apical tooth, in which characters it resembles P. leonensis (Sprague) Balle, P. nigritana (Hook. f. ex Benth.) Balle, and P. vignei Balle, but differs from all of them by the apex of the corolla lobes being thickened into a conical appendage (vs not appendaged) and its smaller anthers, 0.7–1.0 mm long (vs 1.5–3.5 mm) that are not septate (all its congeners have septate anthers). It is further separated from the first two species by its soon glabrescent lower leaf surface (vs persistently hairy), from the last two by its non-foliaceous bracts not or scarcely exceeding calyx (vs foliaceous and long exceeding it) and its corolla with hairs barbellate for most of their length (vs at their base only).

Description

Hemi-parasitic shrub up to 2 m tall, with pendulous branches; twigs cylindrical, 1–3 mm thick, pubescent with rufous barbellate hairs, then glabrescent. Leaves opposite or alternate; petiole 3–11 mm long, pubescent like the twigs; lamina ovate to oblong, 1.7–7.8 × 0.7–3.1 cm, obtuse to rounded or slightly cordate at base, gradually acuminate or rarely obtuse at apex, coriaceous, initially with sparse rufous barbellate hairs but soon glabrescent on both sides, drying dark brown; secondary veins 3–8 pairs, weakly ascending and rather inconspicuous, arching well before the leaf margin. Flowers axillary, solitary or in fascicles of up to 6, subsessile or with pedicel ≤ 1 mm, densely and shortly pubescent with barbellate hairs. Bract triangular to ovate-oblong, 2.0–3.5 × 0.8–1.2 mm, densely pubescent outside with barbellate hairs, not or slightly exceeding calyx and not hiding it. Receptacle broadly urceolate, 1.0 × 1.3 mm, densely and shortly pubescent with hairs barbellate towards their base. Calyx annular, 0.3–0.7 mm long, pubescent like the receptacle, with minute triangular teeth. Corolla 5 - merous, olive green to yellow, pubescent externally with rufous hairs ≤ 0.7 mm long, barbellate for most of their length; apex of bud swollen, ovoid to ellipsoid, acute, not winged; corolla tube at anthesis 22–30 (– 35) mm long, laterally split to about mid-height, with a globose to ellipsoid basal swelling 2.5–5.0 × 1.5–2.5 mm and a strong constriction just above it; lobes patent to reflexed, narrowly clavate, 4.5–6.5 × 0.8–1.0 mm, thickened at apex into a conical horn 0.5–1.0 mm long, inside hardened and canaliculate with short simple tuberculate hairs towards their base. Stamens glabrous, filaments inrolled, ca 3 mm long, yellow, without apical teeth, anthers yellow to brownish, obovate-oblong, 0.7–1.0 mm long, with thecae often unequal, not septate, connective not appendaged. Style yellow-green, exserted, 29–36 mm long, narrowly 5 - winged, more or less papillose on the angles, gradually narrowing towards a 0.5–1.0 mm long apical neck and ending in a capitate stigma ca 0.3 mm in diameter. Fruits obovoid, 6–7 (– 10) × 3–4 mm when dry, green when immature, red to orange when mature, densely pubescent with hairs barbellate at base, subsessile, crowned with persistent calyx ca 1 mm long.

Distribution and ecology

Phragmanthera bidaultii is, as far as known, endemic to the Sanaga River basin in central Cameroon (Fig. 4). This area is part of the Lower Guinea subcentre of endemism of the Guineo-Congolian Region (White 1979). The species occurs in riparian forest, sometimes on rock slabs, along the banks of the Sanaga River. It is usually parasitic on Hymenocardia ripicola J. Léonard (Phyllanthaceae) but has also sometimes been observed on other (unidentified) tree species.

Phenology

Phragmanthera bidaultii was collected in flowers in February and July, while individuals in fruit were observed in January, February, and July. It has a staggered flowering period, with buds, open flowers, young fruits, and mature fruits sometimes present simultaneously on the same branch.

Etymology

The species is named after the French botanist Ehoarn Bidault, who is one of its collectors. Working for the Missouri Botanical Garden, he has greatly contributed to the botanical exploration of West and Central Africa in recent years.

IUCN conservation assessment

Phragmanthera bidaultii is known from 11 collections representing 11 unique occurrences (all of which are considered still extant, in view of their recent date of collection) and one or two subpopulations. Its extent of occurrence (EOO) is calculated as 11 km 2, whereas its area of occupancy (AOO) is estimated at 8 km 2; both values fall within the limits for Critically Endangered category under criterion B. None of the occurrences is in a protected area. One occurrence is located on the future construction site of the Kikot hydroelectric dam (one location), which will lead to its disappearance, and consequently a decline in EOO, AOO, number of locations, and number of mature individuals. The 10 remaining occurrences, at Ntol-Lébanga islands, are not under direct threat but are situated downstream of another dam, whose planned construction is expected to cause a decline in habitat extent and quality due to lower water levels; since they are very close to one another and may be affected by the same event, they represent a single location. The 11 occurrences represent therefore two locations with regards to the most serious plausible threat (hydroelectric dams). Although according to EOO and AOO values the species corresponds to the Critically Endangered category, it cannot be assessed as such because only one of the three conditions (condition b) is met. The species is known from two locations, a value within the limits of the Endangered category. As the EOO and AOO values also correspond to the Endangered category, i. e. 11 km 2 is <5000 km 2 and 8 km 2 is <500 km 2, we therefore assess the species as Endangered: EN B 1 ab (i, ii, iii, iv, v) + 2 ab (i, ii, iii, iv, v).

Additional material examined

CAMEROON – Central Region • Sanaga, Nkongmelen; 4°14’28”N, 11°07’37”E; 380 m; 15 Feb. 2023; fl., fr.; Bidault et al. 6039; BR, BRLU, MO, WAG, YA • Nkolmelen, île de Mibanga; 4°14’16”N, 11°08’06”E; 298 m; 1 Jul. 2023; fl., fr; Sonké & Simo 7414; BR, BRLU, K, M, MO, P, YA • Nkolmelen, île de Mibanga; 4°13’55”N, 11°07’56”E; 324 m; 2 Jul. 2023; fl., fr.; Sonké & Simo 7430; BR, BRLU, K, M, MO, P, WAG, YA • Nkolmelen, île de Lébanga; 4°14’13”N, 11°07’38”E; 264 m; 3 Jul. 2023; fl.; Sonké & Simo 7438; BR, BRLU, K, M, MO, P, YA • Nkolmelen, île de Lébanga; 4°14’07”N, 11°07’28”E; 287 m; 4 Jul. 2023; fl.; Sonké & Simo 7455; BR, BRLU, K, M, MO, P, YA • Nkolmelen, île de Mibanga; 4°14’02”N, 11°08’16”E; 280 m; 5 Jul. 2023; fl., fr.; Sonké & Simo 7460; BR, BRLU, M, MO, P, YA • Nkolmelen, île de Ponis (sud Lébanga); 4°14’26”N, 11°07’24”E; 250 m; 31 Jul. 2023; fl., fr.; Sonké 7491; BR, BRLU, K, M, MO, P, WAG, YA • Nkolmelen, île de Ponis (sud Lébanga); 4°14’24”N, 11°07’24”E; 249 m; 31 Jul. 2023; fl., fr.; Sonké 7493; BR, BRLU, K, M, MO, P, WAG, YA • Ntol-Lébanga, en amont du site du projet de construction du barrage de Kikot; 4°13’55”N, 11°07’56”E; 367 m; 9 Jan. 2024; fr.; Relevé Cameroun 94; BRLU, MO, P, YA • Tombi, patch forestier sur une dalle rocheuse autour du fleuve Sanaga; 4°09’46”N, 11°01’19”E; 340 m; 17 Mar. 2022; Tcheferi, Dauby & Nzoyeuem 13; BR, BRLU, MO, WAG, YA.

Notes

This species was discovered in 2022 along the Sanaga River. No older collections have been found in herbaria by the authors, and it is unlikely that Polhill and Wiens (1998), who reviewed most collections of African Loranthaceae for their monograph of the family, would have missed this rather distinctive plant.

As discussed in the introduction, Phragmanthera bidaultii differs from all its congeners by its non-septate anthers. The position of the corolla lobes, which are patent to reflexed at anthesis (as opposed to erect in most other Phragmanthera species) is a character shared only with five of its congeners: P. eminii (Engl.) Polh. & Wiens, P. proteicola (Engl.) Polh. & Wiens, P. leonensis (Sprague) Balle, P. nigritana (Hook. f. ex Benth.) Balle, and P. vignei Balle. The first two species, both from the Zambezian region, are the only members of sect. Eubracteatae (Engl.) Polh. & Wiens (Polhill and Wiens 1998), which differs from the rest of the genus by the presence of an apical tooth on the stamen filaments. They are also generally much hairier than P. bidaultii and not susceptible of confusion. The last three species, from West and Central Africa, are part of sect. Rufescentes (Engl.) Polh. & Wiens (Polhill and Wiens 1998), and it is with them that P. bidaultii shares the most similarities (differences are summarized in Table 1).

Following the sectional classification of Polhill and Wiens (1998), P. bidaultii should be included in sect. Rufescentes, since it combines a style with a distinct neck under the stigma, corolla lobes hardened inside, and stamen filaments without an apical tooth. A case could be made for placing the species in a new section, due to the unusual character of non-septate anthers, but we think that would be premature in the absence of molecular data. No molecular phylogeny of the genus is available to date – only two species having so far been included in phylogenetic analyses (Vidal-Russell and Nickrent 2008; Liu et al. 2018) – and it remains unclear whether the sections currently recognized represent natural groups.