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| Rhipidoglossum fischerianum A.R.Macedo & Farminhão, in Macedo, Trovó, Stévart et Farminhão. 2025. |
Abstract
Background and aims – Rhipidoglossum is the third most species-rich epiphytic orchid genus in continental Tropical Africa, containing at least 53 species. As part of an ongoing taxonomic revision, a new species endemic to the Western Rift Valley was identified. The novelty was previously confused with R. adoxum and R. globulosocalcaratum. Here, we aim to clarify the diagnostic traits and geographic distribution of these three species.
Material and methods – We applied standard herbarium taxonomic practices to a geographically representative sampling of dry and spirit specimens identified as R. adoxum and R. globulosocalcaratum, and conducted a thorough review of regional floras and field photographs to compile all available information on the novelty. A synoptic table, distribution map, and the risk of extinction based on IUCN Red List conservation status accompany the description and illustration of this new species.
Key results – Rhipidoglossum fischerianum sp. nov., R. globulosocalcaratum, and R. adoxum can be distinguished from each other based on stem size, leaf apex, perianth, and rostellum morphology. Rhipidoglossum fischerianum is endemic to the lower montane forests in the Western Rift, whereas R. globulosocalcaratum is restricted to the Guineo-Congolian forests, and newly recorded from Cameroon and Uganda. Rhipidoglossum adoxum is found in montane forests of Ethiopia, Kenya, and South Sudan. The new species is preliminarily assessed as Vulnerable (VU). The name R. globulosocalcaratum is here lectotypified.
Conclusion – This new species increases the diversity of Rhipidoglossum in the Western Rift to 16 species, of which 10 are endemic or near-endemic to the region. It highlights the relevant role of ongoing taxonomic work and the preservation of the Western Rift forests, which harbour high levels of unique biodiversity.
Keywords: Afromontane, African biogeography, Afrotropical biodiversity, Albertine Rift, East African Rift Valley, Ethiopian Highlands, IUCN, lectotypification, root gall, Virunga mountains
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| Rhipidoglossum fischerianum. A. Habit. B. Stem apex with two inflorescences. C. Leaf. D. Flower: frontal view. E. Flower: lateral view. F. Dorsal sepal. G. Lateral sepals. H. Petals. I. Lip: superior view. J. Lip: inferior view. K. Column: lateral view. L. Column: frontal view. M. Anther cap: frontal view. N. Anther cap: posterior view. O. Pollinaria. P. Fruit. Illustration from B. Dumbo 17 (holotype, BRLU). Drawn by Roger Andriamiarisoa. |
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| Watercolour of Rhipidoglossum fischerianum [BR0000006800420]. Prepared by Gilbert Delepierre, December 1991. |
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| Rhipidoglossum fischerianum. A. Habit. B. Habit with close-up of a root gall (J. Farminhão & B. Dumbo 233, BRLU). C. Habit (Gisenyi). D. Inflorescences (Cyamudongo Forest, from holotype B. Dumbo 17, BRLU). E. Flower: inferior view, showing spur (Gishwati Forest, unvouchered). Photographs by João Farminhão (A, B), Eberhard Fischer (C, E), and Bonny Dumbo (D). |
Rhipidoglossum fischerianum A.R.Macedo & Farminhão, sp. nov.
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).
Arthur Macedo, Marcelo Trovó, Tariq Stévart and João Farminhão. 2025. A New Species of Rhipidoglossum (Orchidaceae, Angraecinae) from the Western Rift Valley (Africa). Plant Ecology and Evolution. 158(2): 248-259. DOI: doi.org/10.5091/plecevo.155517
