Rhipidoglossum acuminifolium A. R. Macedo & Farminhão sp. nov.

Figs 2, 3, 4, Table 1

Type.

Cameroon • Southwest: Fako District, Mount Cameroon, Mann’s Spring, 2150 m, 16 Aug 2019, Š. Janeček s. n. (holotype BRLU s. n.!, isotype YA!).

Diagnosis.

Rhipidoglossum acuminifolium is most similar to Rhipidoglossum delepierreanum, but can be distinguished by the following characteristics: leaf shape (narrowly elliptic-falcate to narrowly oblong-falcate vs. elliptic-falcate to oblong-falcate), including the apex (very unequally bilobed, larger lobe acute to acuminate, 12–19 mm long vs. unequally bilobed, larger lobe 7–11 mm long), and longer spur (14.2–15 mm long vs. 6–8 mm long) (Table 1).

Description.

Epiphytic herb, pendent, up to 120 cm long. Roots slender, basal and axillary, usually one per node, greenish-whitish, ca. 300 mm × 2 mm. Stem pendent, slender, rarely branched, up to 300 × 2–5 mm, internodes 20–30 mm long. Leaves up to 15, distichous, concolorous, narrowly elliptic-falcate to narrowly oblong-falcate, entire, margin slightly undulate, apex unequally bilobed, larger lobe 12–19 mm long, acuminate, base attenuate, 56–197 × 14–37 mm. Inflorescences up to 7, dense, 1 (– 2) per node, axillary, pendent, shorter than leaves, 17–25 - flowered, 40–102 mm long; peduncle glabrous, 3–6 mm long; rachis glabrous, green, 37–96 mm long; bracts ochreate, whitish, 1.5 × 2 mm. Flowers whitish to pale green, pale orange during late anthesis. Pedicel and ovary cylindrical, scurfy, with dark brown scales, 5–6 × 1–1.3 mm; dorsal sepal elliptic, apex acute, base obtuse, entire, 5–5.5 × 3–3.2 mm, lateral sepal narrowly elliptic, apex and base attenuate, entire, 8–8.5 × 2.3–2.5 mm; petals elliptic to ovate, apex acute to slightly acuminate, base obtuse, entire, 5.8–6 × 3.3–3.5 mm, lip flabellate, apex bilobed, lateral margin crenulate, apical margin incised, convex, ecallose, 5.6–7.5 × 11–12 mm; spur cylindrical, acute at apex, curved, whitish to pale green 14.2–15 × 0.2–2 mm; column whitish to pale green, 2.2–2.4 mm long; anther cap galeate, frontal margin slightly undulate, whitish, 1.7–1.8 × 1.7–1.8 mm, stipites two, obclavate, translucid, viscidia two, depressed ovate, yellowish; pollinia two, orbicular, yellowish, 0.7 × 0.7 mm; rostellum trilobed, lateral lobes reduced, subtriangular, midlobe oblong with a globose apex, 1.7–1.8 × 0.7 mm. Fruit a capsule, elliptic, ribbed, 15.5–17.9 × 6.3–6.5 mm.

Distribution.

Equatorial Guinea (Bioko) and Cameroon (Fig. 4). Rhipidoglossum acuminifolium occurs in submontane to montane forest patches along the Cameroon Volcanic Line, between 550–2165 m a. s. l.

Habitat and ecology.

Rhipidoglossum acuminifolium is a trunk epiphyte, occasionally growing on lianas, occurring in primary and secondary montane and submontane forests, in partly shaded areas, at 2–5 meters above the ground, often forming large clumps hanging from the phorophyte (see Suppl. material 2). In the studies on the plant – pollinator interactions on Mount Cameroon, the first flower visitor records of R. acuminifolium were identified (Klomberg et al. 2022; Sakhalkar et al. 2023; Uceda-Gómes et al. 2023) (Fig. 5). The moth Afroracotis cf. squalida (Lepidoptera, Erebidae) successfully removed the pollinia from the column and carried them away dorsally attached to the proximal (basal) part of the proboscis (Fig. 5 A, B). Another settling moth species, Paschiodes sp. (Lepidoptera, Erebidae), was observed visiting the flowers (Fig. 5 C). In addition, insect visitors included an unidentified ametroidine raspy cricket, cf. Glomeremus sp. (Orthoptera, Gryllacrididae, Ametroidini) (Fig. 5 D, E), fruit flies of the genera Zaprionus Coquillett, 1902 (Fig. 5 F), Drosophila Fallén, 1823 and or Scaptodrosophila Fallén, 1823 (Diptera, Drosophilidae) (Fig. 5 G), and two unidentified species of calyptrate muscoid flies (Diptera, Calyptratae) (Fig. 5 H, I). The records also include an unidentified parasitoid wasp (Hymenoptera) (Fig. 5 J) (Klomberg et al. 2022). The only bird visitor recorded was the Northern Double-collared Sunbird (Cinnyris reichenowi Sharpe, 1891) (Fig. 5 K), which was observed feeding on nectar obtained directly from the spur (Fig. 5; Suppl. materials 3 –11). This species is unlikely to play a role in the effective pollination of R. acuminifolium, acting instead as a nectar thief. In contrast, settling moths are considered the most likely primary pollinator group, owing to pollinia removal and their frequent contact with the column (Klomberg et al. 2022). Rhipidoglossum acuminifolium has been recorded in association with a diverse assemblage of orchid species, such as Aerangis gravenreuthii (Kraenzl.) Schltr., Angraecopsis tridens (Lindl.) Schltr., Bulbophyllum deshmukhii U. B. Deshmukh & J. M. H. Shaw, Polystachya cooperi Summerh., and Rhipidoglossum confusum (P. J. Cribb) Farminhão and Stévart. (African Plant Database 2025; GBIF 2025; V. Droissart pers. obs.).

Phenology.

Flowers in the wet season from June to late August, and January. Fruits observed in November.

Etymology.

The specific epithet acuminifolium refers to the shape of the larger lobe on the leaves of this species. This feature is the most evident trait used to differentiate it from its closest relative.

Preliminary IUCN conservation assessment.

Rhipidoglossum acuminifolium is known from six herbarium and spirit samples and one observation representing seven occurrences, the most recent made in 2021. Except for one (photographic) observation (in Bandoumkassa, Cameroon), all occurrences were made inside or associated with officially protected areas (Mount Cameroon National Park and Sanctuaire de Banyang Mbo, Cameroon; Gran Caldera de Luba Scientific Reserve, Equatorial Guinea (Bioko Island)), and they can be considered as still existing occurrences. These occurrences represent four biogeographical subpopulations. Three subpopulations occur in each of the three protected areas cited above. Four locations were identified with respect to the most serious plausible threat known to the ecosystems in the Cameroon Volcanic Line: habitat degradation due to the combined effects of deforestation for small-scale agriculture, road and urban expansion and potentially small-scale timber extraction (Solefack et al. 2012; Lézine et al. 2025). Evidence of direct human impact on the vegetation, small-scale agriculture, presence of buildings, and landscape changes is notable close to the Gran Caldera de Luba Scientific Reserve, Equatorial Guinea, as well as in the limits of the Mount Cameroon National Park, in Cameroon. The Sanctuaire de Banyang Mbo, also in Cameroon, appears to be a relatively stable conservation unit, with little evidence of landscape and vegetation changes, presence of crop species and buildings. The Bandoumkassa population is the most vulnerable, occurring outside any protected area and adjacent to human settlements, with intense evidence of urban expansion, agricultural encroachment, landscape alteration and clearance of primary and secondary forests. The extent of occurrence (EOO) is calculated as 6,775 km ² (falling within the limits for Vulnerable status under criterion B 1), whereas its area of occupancy (AOO) is estimated at 16 km ² (within the limits for Endangered status under criterion B 2), and the number of locations being equal to 4, within the limits for Endangered status under criterion Ba. The projected loss of the Bandoumkassa subpopulation, and contraction of its area of occupancy, is associated with a continuing decline in EOO, AOO, habitat extent and quality, and mature individuals (b i, ii, iii, iv). Rhipidoglossum acuminifolium is thus assigned a preliminary risk of extinction status of Endangered: EN B 2 ab (i, ii, iii, iv).

Paratypes.

Cameroon • Southwest: Koupé-Manengouba, Sanctuaire de Banyang Mbo, Village de Bejange, 550 m, 1 Feb 2008, st., V. Droissart 648 (BRLU s. n.); • District Fako, Mount Cameroon, “ loc. 11 ”, 17–18 Jun 1973, fl., R. Linnavuori s. n. (H [H 1259726, H 1210167]); • ibid. loc., near Mann’s spring, 2165 m, 14 Aug 2019, fl., Š. Janeček s. n. (BRLU s. n.). Equatorial Guinea • Bioko: Caldera [de] San Carlos to Ruiché, 11 Jan 1967, fl., W. W. Sanford 4360 (K s. n.).