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

Figs 4, 6, 7, Table 2

Type.

Central African Republic • Lobaye: Mbaiki, Région de Boukoko, 20 Jul 1951, C. Tisserant et al. 2185 (holotype P [P 00388648!], isotypes P [P 00388649!], G [G 208985!]).

Diagnosis.

Rhipidoglossum falcatulum is similar to Rhipidoglossum curvatum but can be distinguished by the following characteristics: stems (up to 15 vs. up to 5 leaves); leaf shape (linear to falcate leaves, with a strongly acute apex vs. obovate to rarely elliptic, apex acuminate to bilobed); shorter inflorescences (up to 151 mm long vs. 570 mm long); and smaller flowers, with a minute semilunular, convex to slightly concave, ecallose lip lamina (vs. conspicuous, broadly ovate, concave lip lamina, with a rim-like semicircular callus) (see Table 2).

Description.

Small epiphytic herb, up to 60 mm long. Roots slender, mostly basal and numerous, axillary only at the lower nodes of the stem, one per node, greenish-whitish, 20–61 × 1–2 mm. Stem pendent, slender, unbranched, up to ca. 60 × 1–2 mm, internodes 2.5–5 mm long. Leaves up to 15, distichous, linear-lanceolate to falcate, entire, apex strongly acute, base attenuate, 35–95 × 5–8.5 mm. Inflorescences 1–6, lax, up to 2 per node, axillary, pendent, usually longer than leaves, 16–28 - flowered, 48–151 mm long; peduncle glabrous, 11–34 mm long; rachis glabrous, 37–117 mm long; bracts ochreate, 1 × 1 mm, peduncle bracts larger. Flowers small, pale yellow-green, except for greenish white spur. Pedicel and ovary cylindrical, slender, sparsely scaly, 4–5 × 0.5–0.6 mm; dorsal sepal elliptic, apex obtuse, base rounded, entire, 2.3–2.5 × 1–1.2 mm, lateral sepal lanceolate, apex acuminate, base shortly oblong, entire, 2.3–2.5 × 1–1.2 mm; petals elliptic to ovate, apex obtuse, base rounded, entire, 1.2–1.5 × 1–1.2 mm, lip semilunular, apex obtuse, margin entire, convex to slightly concave, ecallose, 0.7–0.8 × 1.5–1.7 mm; spur cylindrical, acute at apex, slightly to strongly curved, 10–12 × 0.5–1.7 mm; column whitish, 1–1.2 mm long; anther cap frontal margin slightly bilobed, with irregularly serrate lobes, whitish-translucent, 0.8–0.9 × 0.8–0.9 mm; stipites two, obclavate, 0.4 mm long, viscidia two, piriform, whitish-translucent; pollinia orbicular, whitish, 0.3 × 0.3 mm; rostellum trilobate, lateral lobes reduced, subtriangular, midlobe oblong, finger-shaped, slightly prominent, apex rounded, shortly longer than the lateral lobes, decurved, 0.46–0.48 × 0.1 mm. Fruit not seen.

Distribution.

Central African Republic and Democratic Republic of the Congo, 550–1045 m a. s. l. (Fig. 4). Its small size makes detection difficult, which may partly explain the limited number of specimens and the apparent c. 1,200 km disjunction between known localities in the northern and southern DRC. We therefore expect R. falcatulum to be more widely distributed across the lowland Guineo-Congolian forests of Central Africa. Additional botanical surveys are needed to clarify the species distribution range.

Habitat and ecology.

Rhipidoglossum falcatulum is a rare trunk epiphyte. It was documented in the lowland semi-deciduous Congolian rainforest (approx. 550 m a. s. l.) in the Central African Republic (CAR), in the wetter lowland Congolian rainforest characterised by monodominant patches of Gilbertiodendron dewevrei (De Wild.) J. Léonard (approx. at 420 m a. s. l.) in the northern DRC, and in the Central Zambezian miombo woodland, specifically within the muhulu vegetation fragments (ca. 1,045 m a. s. l.) in southern DRC. In northern DRC, it was recorded growing on Isolona hexaloba (Pierre) Engl. et Diels. In southern DRC, it was recorded growing on Englerophytum magalismontanum (Sond.) T. D. Penn. In CAR, it was collected together with Cyrtorchis brownii (Rolfe) Schltr., a species typical of seasonally tropical dry forests (Azandi et al. 2016).

Phenology.

Flowers from June to late August, and January. Fruits not observed to date.

Etymology.

The specific epithet refers to the small falcate leaves, and spur, important diagnostic character of this taxon.

Preliminary IUCN conservation assessment.

Rhipidoglossum falcatulum is known from seven occurrences based solely on herbarium samples, the most recent collected in 1986. No occurrences were found inside or associated with official protected areas. The seven occurrences represent a total of four biogeographical subpopulations known so far, still believed to exist, considering the presence of native vegetation. They were recorded in the lowland Guineo-Congolian forests close to Boukoko (CAR) and Kisangani (northern DRC), and in dry evergreen forests (“ muhulu ”) forests, among miombo woodland, close to Kyamasumba (Upper Katanga, DRC). It occurs in four locations with respect to the most serious plausible threat: small-scale agriculture, commercial logging, urban expansion, and slash-and-burn methods for animal husbandry (Blankespoor 1991; Logan and D’Andrea 2012; Burivalova et al. 2015; Delan 2021). Direct human impacts on the vegetation are evident in all locations, including buildings and marked landscape changes for agriculture and animal cultivation. The extent of occurrence (EOO) is calculated as 509,612 km 2 (being considered as Least Concerned 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 3, within the limits for Endangered status under criterion Ba. The projected loss of both subpopulations due to the factors cited above, and contraction of their area of occupancy is associated with a continuing decline in EOO, AOO, habitat extent and quality, and mature individuals. Based on the currently available data, considering our current interpretation of its biology and the potential area of distribution for this taxon, Rhipidoglossum falcatulum is assigned a preliminary extinction risk status of Endangered: EN B 2 ab (i, ii, iii, vi, v).

Paratypes.

Central African Republic • Lobaye: Mbaiki, Région de Boukoko, ca. 550 m, 19 Jul 1949, R. P. Tisserant et al. 1537 (P [P 00388650, P 00388651], G [G 208970]); • ibid. loc., 10 Aug 1950, R. P. Tisserant et al. 2626 (BM [BM 000540025], P [P 388644, P 00388645]). Democratic Republic of Congo • Tshopo: Banalia, 23 km along road from Kisangani to Bengamisa, 21 Jun 1973, J. Bokdam 4189 (WAG [WAG.1140141]). • Lualaba: Mutshatsha, muhulu de Kyamasumba, 42 km NNW of Kolwezi, 1040 m, 2 Jan 1982, M. Schaijes 1298 (BR [BR 25200010, BR 6102008084335 - spirit]; • ibid loc.; fl. in cult. 1983, M. Schaijes 1918 (K [K-SPC 47374]); • ibid. loc., forêt dense sèche sur sable, 1075 m, 20 Jan 1986, M. Schaijes 2838 (K [K-SPC 50377]).