Rhipidoglossum fischerianum A. R. Macedo & Farminhão, 2025

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

Figs 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , Table 1 View Table 1

Type

RWANDA – Western Province • Rusizi district, Cyamudongo Forest (Nyungwe National Park), Kaboza ; 2°33’06.94”S, 28°59’19.68”E; ca 1900 m; 23 Oct. 2019; fl.; B. Dumbo 17; holotype: BRLU; isotype: K GoogleMaps .

Diagnosis

Rhipidoglossum fischerianum is most similar to R. globulosocalcaratum and R. adoxum , but can be distinguished by the following characteristics: leaves dark green, linear-falcate with acute apex (vs light green, narrowly oblong with unequally bilobed apex in R. globulosocalcaratum ; vs dark green, linear-falcate with unequally bilobed apex in R. adoxum ); inflorescences with fewer flowers, 3–5 (vs 4–9 in R. globulosocalcaratum ; vs 8–11 in R. adoxum ); larger lateral sepals, widely ovate, 3–3.3 × 1.5–1.7 mm (vs widely elliptic to subcircular, 2.1–2.2 × 1.7–1.8 mm in R. globulosocalcaratum ; vs triangular to widely deltate, 2.3–2.5 × 0.8–0.9 mm in R. adoxum ); lip subcircular, markedly concave and bowl-shaped, spreading (vs transversally elliptic, convex, decurved in R. globulosocalcaratum ; vs ovate, concave, decurved in R. adoxum ); a lemon anther cap with a small pointed zenithal projection (vs pale yellow anther cap rounded at the zenith in both species); oblong viscidia with acute extremities, enclosed onto the sides of the rostellum (vs ellipsoid viscidia and rounded extremities, enclosed onto the sides of the rostellum in R. globulosocalcaratum ; vs subcircular, exposed laterally to the rostellum midlobe in R. adoxum ).

Description

Epiphytic, pendent herb, up to 300 mm tall. Roots slender, basal and axillary, usually 2 (– 4) per node, distributed all along the stem, greenish – whitish, 15–90 × 7–15 mm. Stem spreading to pendent, elongate, rarely branched, up to 300 × 1.5–2 mm, internodes 2–6.5 mm long. Leaves usually 20–30 (46), distichous, dark green, concolourous, linear-falcate, entire, apex acute, base attenuate, 13–82 × 1–4.5 mm. Inflorescences up to 2 per node, axillary, much shorter than the leaves, 3–5 - flowered, 9–12 mm long; peduncle glabrous, 4.5–6.5 mm long; rachis glabrous, 4.5–5.5 mm long; bracts deltate, 1 × 0.7–1.3 mm. Pedicel and ovary cylindrical, glabrous, 3.5–5.3 × 0.7 mm; dorsal sepal widely elliptic to widely ovate, apex obtuse, white to ivory, margin entire, 3 × 2–2.2 mm, lateral sepals widely ovate, apex acute, white to ivory, margin entire, 3–3.3 × 1.5–1.7 mm; petals widely elliptic, apex acute, slightly concave, white to ivory, margin entire, 2.3–2.5 × 1.7–1.8 mm, lip subcircular, markedly concave, bowl-shaped, spreading, white to ivory, margin slightly involute, lacking a callus, 2.1 × 2.4–2.5 mm; spur cupuliform, straight, greenish – whitish, 1.4–2 × 1 mm; column bright green, decurved, ca 1.5 mm long; anther cap with a small pointed zenithal projection, frontal margin rounded, lemon-coloured, 0.8 × 0.8 mm; stipes two, obclavate, viscidia two, oblong, acute extremities, translucid, enclosed in the viscidium; pollinia two, globose, 0.5 × 0.5 mm; rostellum trilobate, lateral lobes reduced, triangular, midlobe nose-shaped, with prominent lateral viscidial cavities, slightly recurved, ca 0.7 × 0.7 mm. Fruit, a capsule, globose, ribbed, 6 × 3.8–4 mm.

Distribution

Rhipidoglossum fischerianum is endemic to the Western Rift Valley in Central and Eastern Africa, occurring in the Democratic Republic of the Congo, Uganda, and Rwanda, between 1900 and 2605 m a. s. l. (Fig. 1 View Figure 1 ).

Habitat and ecology

Rhipidoglossum fischerianum is an epiphytic herb occurring in primary and secondary lower montane forests. In Nyungwe and Kahuzi-Biéga National Parks, it was observed growing on trunks and large branches at 2.5–4 m above the ground, in full sun and partly shaded areas, in forests dominated by Carapa wohllebenii Eb. Fisch., Killmann, Leh & S. B. Janssens , and Newtonia buchananii (Baker) G. C. C. Gilbert & Boutique , with Myrianthus holstii Engl. , Polyscias fulva (Hiern) Harms , Entandrophragma excelsum (Dawe & Sprague) Sprague , and Symphonia globulifera L. f.; as well as in swamp forest with Syzygium parvifolium, (Engl.) Mildbr. , Carapa wohllebenii , Anthocleista grandiflora Gilg , and Afrocarpus usambarensis (Gilg) C. N. Page. It can also be found in heath swamp. Recorded phorophytes include Erica sp. , Ficus sp. , Millettia dura Dunn , Myrianthus holstii , and Xymalos monospora (Harv.) Baill. A root gall was observed in one specimen (J. Farminhão & B. Dumbo 233), collected in Cyamudongo Forest (Fig. 5 View Figure 5 ).

Column morphology

Rhipidoglossum fischerianum presents a bulging rostellum midlobe with two prominent lateral cavities enclosing the viscidia. This morphology, shared with R. globulosocalcaratum , vaguely resembles a human nose: the “ nostrils ” are the viscidial cavities; the “ columella ” the midlobe apex. This ‘ nose-shaped rostellum’, as first coined herein, is conspicuously different from the slender, axe-shaped, midlobe of R. adoxum (see Rasmussen 1974: 230), in which the viscidia are laterally exposed, immediately before the auricles of the apex. Dissected flowers revealed an unusual column morphology, characterised by an inward curvature and slight inflation. These traits may reflect post-pollination modifications. Further investigations to confirm the prevalence of this phenomenon within the genus are still required.

Phenology

Flowers between (July) late August and December (March). Fruits were observed in March, September, and December.

Etymology

The epithet celebrates Eberhard Fischer, PhD, Professor at the University of Kaiserslautern-Landau (formerly University of Koblenz-Landau) for his outstanding contributions to the floristics and taxonomy of the orchids of the Western Rift region.

Preliminary IUCN conservation assessment

Rhipidoglossum fischerianum is known from 12 herbarium and spirit samples and six observations representing 18 existing occurrences, the most recent made in 2021. Except for one observation in (Gisenyi, Rwanda), all occurrences were made inside or associated with official protected areas (Bwindi Impenetrable Forest National Park, Uganda; Volcanoes National Park, Gishwati Forest (Gishwati-Mukura National Park), and Nyungwe National Park ( Rwanda); and Kahuzi-Biéga National Park ( Democratic Republic of the Congo). The 18 existing occurrences represent a total of seven subpopulations corresponding to each protected area or forest block (Bwindi Impenetrable Forest National Park, Volcanoes National Park, Gisenyi, Gishwati Forest, Nyungwe National Park, Cyamudongo Forest, and Kahuzi-Biega National Park). The occurrence area is considered severely fragmented due to urban and agroforestry encroachment for tea plantations, and 8 locations with respect to the most serious plausible threat, habitat degradation due to the combined effects of forestry (tea and pine plantations), urban expansion and mining exploration. Habitat degradation driven by urban expansion, subsistence agriculture, tea and Pinus patula Schiede ex Schltdl. & Cham. plantations are the main threat over the Gisenyi subpopulation ( Chao et al. 2011; Plumptre et al. 2016, 2020), the only unprotected subpopulation, recorded once in 2009. Virtually no native forest was left around Gisenyi city, where this subpopulation is likely near or completely extinct. Evidence of direct human impact on the vegetation, logging, buildings, and landscape degradation is notable within Kahuzi-Biéga National Park. In contrast, the largest population, located within Nyungwe National Park, appears to be in a relatively stable conservation unit. The extent of occurrence (EOO) is calculated as 6,850 km 2 (falling within the limits for Vulnerable status under criterion B 1), whereas its area of occupancy (AOO) is estimated at 52 km 2 (within the limits for Endangered status under criterion B 2), and the number of locations being equal to 8, within the limits for Vulnerable status under criterion Ba. The projected loss of the Gisenyi subpopulation, and contraction of the area of occupancy in the Kahuzi-Biega subpopulation, is associated with a continuing decline in EOO, AOO, habitat extent and quality, and mature individuals. Rhipidoglossum fischerianum is thus assigned a preliminary risk of extinction status of Vulnerable: VU B 1 ab (i, ii, iii, iv).

Additional specimens (paratypes) examined

UGANDA – Western Province • Kigezi ; Sep. 1936; fl. bud; W. J. Eggeling 3238; K [ K 000874506 ] .

RWANDA – Northern Province • Musanze, Virunga Mountains ; fl. in cult. 20 Aug. 1986; H. Campbell s. n.; K . – Western Province • Karongi district, Nyungwe, piste Gisovu ; s. d.; fl.; G. Delepierre 174; BR spirit [ BR 6102016347583 ] • Gisakura , cult. in Kigali; 1978; fl. in cult.; P. De Wanckel in G. Troupin 15949; BR [ BR 0000006802615 ] • Nyamasheke district, Parc National Nyungwe, Kamiranjovu [Kamiranzovu swamp] ; 19 Mar. 1956; A. R. Christiansen 1452; BR [ BR 0000025200188 ] • ibid.; Jul. 1975; fl. in cult. in Dec. 1975; G. Troupin 15757; BR [ BR 0000006799762 , BR 6102008659267 spirit] • Rusizi district, Cyamudongo Forest, Kaboza ; 20 Sep. 2021; fl.; cult. in Huye; E. Fischer s. n.; BRLU • ibid., cult. in Butare; 02°33’48”S, 28°58’59”E; 2029 m; 30 Jan. 2018; st.; J. Farminhão & B. Dumbo 233; BRLU, spirit GoogleMaps .

DEMOCRATIC REPUBLIC OF THE CONGO – Sud Kivu Province • Beni, Kabare, Kahuzi Biega National Park ; 2°10’48.68”S, 28°39’58.024”E; 2605 m; 15 Jun. 2018; fl. in cult. in Lwiro 21 Oct. 2019 and in Huye 20 Aug. 2020 / 7 Sep. 2020; L. Dumbo & B. Dumbo 1; LWI GoogleMaps • Beni, Kabare, Kahuzi Biega National Park, Tshibati Sector ; 2°11’55.94”S, 28°46’58.70”E; 2125 m; 16 May 2010; J. de D. Mangambu Mokoso 2888; BR [ BR 0000005596300 ] GoogleMaps .