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| Ypsilopus zimbabweensis Farminhão & P.J.Cribb, in Farminhão & Cribb, 2023. |
Abstract
Background and aims – A preliminary review of hawkmoth-pollinated angraecoids from Africa unveiled a remarkable case of parallel evolution of extreme column exsertion between the two species formerly classified in in the defunct genus Barombia. These belong to one clade of Aerangis, including A. gracillima and A. stelligera, and Ypsilopus sect. Barombiella, including Y. amaniensis and Y. schliebenii. The exploration of the geographical distribution of these two clades, followed by an examination of morphological variation within Y. sect. Barombiella, revealed that the disjunct population identified as Y. amaniensis from Zimbabwe represents an undescribed species.
Material and methods – Occurrence records of Ypsilopus amaniensis, Y. schliebenii, Aerangis gracillima, and A. stelligera were comprehensively mapped and distribution patterns were visually analysed. Pollination syndromes and pollinaria attachment sites were inferred based on a review of floral and hawkmoth morphology. Standard herbarium practices and mining of photographs of wild and cultivated plants in social media allowed the description of the novelty.
Key results – Ypsilopus zimbabweensis sp. nov. (Y. sect. Barombiella) is a narrow endemic of significant horticultural interest and it is preliminarily assessed as Endangered. The evolution of a Barombia-type column presents a parallel geographical pattern in the Aerangis gracillima–A. stelligera clade and Ypsilopus sect. Barombiella and probably induced a shift of pollen placement sites in these sphingophilous species.
Keywords: Great Zimbabwe National Monument, iNaturalist, lithophytic orchids, sphingophily, taxonomy, Tropical Africa
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| Possible evidence for reinforcement in the geographical distribution and hypothetical pollinaria attachment sites (on a large sphingid hawkmoth) of two angraecoid clades with divergent column exsertion lengths in tropical Africa. Aerangis gracillima (yellow triangles) is closely allied to A. stelligera (blue triangles), while Ypsilopus amaniensis (blue diamonds) is closely related to Y. schliebenii (yellow diamonds). An extremely elongated Barombia-type column is present in A. gracillima and Y. schliebenii. The three isolated collections of Y. amaniensis in Zimbabwe are here assigned to Ypsilopus zimbabweensis (white diamonds). Photos by Murielle Simo-Droissart (A. gracillima), Bart Wursten (A. stelligera), Guido van Asten (Y. amaniensis), and Russell Hutton (Y. schliebenii). |
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| Ypsilopus zimbabweensis. A. Plants growing as lithophytes in situ. B. Inflorescence, side view, of plant cultivated in Harare. Photos by Bart Wursten (A) and Isobyl la Croix (B). |
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| Ypsilopus zimbabweensis. A. Habit. B. Flower, side view. C, D. Flower, front view. E. Lip margin variability. F. Column, ventral view, with glandular trichomes visible. G. Anther cap, side, dorsal, and ventral views. H. Viscidium and stipes. I. Pollinium (one of two). A (in part), E (in part), F–I drawn from the type collection; A, E (both in part) and I from Jackson 56814; B, C after watercolour by Patricia van de Ruit. All drawn by Andrew Brown. |
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| Watercolour of Ypsilopus zimbabweensis, originally identified as Rangaeris amaniensis, by Patricia van de Ruit, published in Ball (1978: 1394). Reproduced with permission. |
Ypsilopus zimbabweensis Farminhão & P.J.Cribb, sp. nov.
Diagnosis: Closely allied to Ypsilopus amaniensis (Kraenzl.) D’haijère & Stévart from eastern Africa but differs in having longer leaves (80–130 mm vs 35–115 mm in Y. amaniensis), inflorescences that greatly exceed the leaves, bearing 10–13 flowers (vs 5–8 in Y. amaniensis), and having a longer peduncle (45–70 mm vs 10–15 mm) and rachis (120–170 mm vs 50–80 mm).
Distribution: Endemic to the Central Watershed of Zimbabwe, in the inselbergs of the southern middleveld margin of the Zimbabwe Craton, west of the Save River, in Masvingo Province (Fig. 1).
Etymology: The species is only recorded from Zimbabwe, namely from the area around the Great Zimbabwe National Monument, which gives the country its name.
João Farminhão and Phillip J. Cribb. 2023. A New Ypsilopus (Orchidaceae, Angraecinae) from Zimbabwe and Notes on the parallel evolution of extreme column exsertion in African angraecoids. Plant Ecology and Evolution. 156(3): 374-382. DOI: 10.5091/plecevo.107313
