Research Article |
Corresponding author: João Farminhão ( joao.farminhao@gmail.com ) Academic editor: Isabel Larridon
© 2023 João Farminhão, Phillip J. Cribb.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Farminhão J, Cribb PJ (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. https://doi.org/10.5091/plecevo.107313
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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.
Great Zimbabwe National Monument, iNaturalist, lithophytic orchids, sphingophily, taxonomy, Tropical Africa
The evolution of mechanical barriers leading to pollen placement shifts (i.e. changes of the position of pollen loads on pollinators) are exclusively reported in plants with high floral integration (i.e. coordinated covariance of floral traits) and accuracy (
A preliminary review of hawkmoth pollination in angraecoid orchids (
To better understand this parallelism, we explored the geographical distribution of A. stelligera, A. gracillima, Y. amaniensis, and Y. schliebenii and examined in further detail morphological variation within these taxa, with a focus on the two species of Ypsilopus Summerh.
Ypsilopus is an angraecoid genus (from the cyrtridactyloid clade) confined to eastern and southern Africa, which encompasses 12 species arranged in two sections, comprising species formerly included in Tridactyle Schltr and Rangaeris (Schltr.) Summerh. (
We mapped all occurrences of A. gracillima, A. stelligera, Y. amaniensis, and Y. schliebenii vouchered by specimens deposited in BR, BRLU, P, K, and SRGH using QGIS v.3.4.15.
We compiled spur length and column measurements for the same angraecoid species based on a comprehensive literature survey (
We applied standard herbarium practices to investigate the variability of plants identified as Y. amaniensis kept at BR, K, and SRGH, including reproductions of specimens kept at FI, and all type material (acronyms following
IUCN Red List categories and criteria (
In Aerangis Rchb.f. and Ypsilopus, the Barombia-type column that has evolved in parallel occurs in the species with the narrowest distribution, which is marginal to the range of the most widespread taxa with shorter columns (Fig.
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).
The range of spur and column length in the studied angraecoids is summarised in Table
Spur and column lengths in the Aerangis gracillima–A. stelligera clade and Ypsilopus sect. Barombiella.
Spur length (cm) | Column length (cm) | |
Aerangis gracillima | 18–25 | 3–4 |
Aerangis stelligera | 14–25 | 1–1.5 |
Ypsilopus amaniensis | 8–16 | 0.5 |
Ypsilopus schliebenii | 16–17.5 | 2–2.7 |
Ypsilopus zimbabweensis | 11–14 | 0.5 |
Ypsilopus zimbabweensis can be morphometrically separated from Y. amaniensis namely according to leaf length, flower number, and peduncle length. Differences are summarised in the taxonomic treatment.
Distribution of A. gracillima, A. stelligera, Y. amaniensis, and Y. schliebenii is consistent with different floristic bioregions of the Afrotropics (
Considering spur length (see
Populations previously identified as Y. amaniensis in Zimbabwe are here recognised as Ypsilopus zimbabweensis sp. nov. The novelty is apparently endemic to the Central Watershed biogeographical area (
1. | Leaves spread along the stem; lip spur at least 7.5 cm long; column glandular, at least 5 mm long | 2 sect. Barombiella |
– | Leaves arranged in a fan; lip spur less than 5 cm long; column eglandular, less than 2 mm |
sect. Ypsilopus (see |
2. | Column longer than 2 cm | Y. schliebenii |
– | Column up to 2 cm long | 3 |
3. | Inflorescence 5–8-flowered; peduncle 1–1.5 cm | Y. amaniensis |
– | Inflorescence 10–13-flowered; peduncle 4.5–7 cm | Y. zimbabweensis sp. nov. |
ZIMBABWE • Masvingo [Victoria District], ± 3 km from Zimbabwe turn-off on Morgenster road; 12 Jan. 1976; J.S. Ball 1394; holotype: K; isotype: SRGH.
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).
Robust, erect or rarely pendent, lithophytic or epiphytic herb, often forming clumps. Roots emerging through the leaf bases opposite the leaves, stout, 8–9 mm in diameter, branching distally, silvery grey. Stems 20–30 or more cm long, 7–9 mm in diameter, covered with sheathing leaf bases. Leaves rigidly coriaceous, 12–16, distichous, twisted just above the basal articulation to lie in one plane, linear-oblong, unequally roundly lobed at the apex, conduplicate at base just above the leaf sheath, 80–130 × 12–19 mm, deep olive-green, articulated to 10–17 mm long leaf sheath. Inflorescences longer than the leaves, arching to pendent, secund in two ranks, 1-several, from leaf sheaths 30–50 mm below the stem apex, 17–23 cm long, 10–13-flowered; peduncle cylindrical, 45–70 mm long, bearing 2–4 sheathing sterile bracts, 5–8 mm long; rachis slenderly cylindrical, slightly zigzag, 12–17 cm long; floral bracts cucullate, ovate, subacute, 6–8 × 4–8 mm. Flowers 22 × 28 mm, showy, white with a buff-tinged spur, the basal flower opening last, diurnally and nocturnally scented of vanilla; pedicel and ovary 22–25 mm long, the ovary scabrid. Sepals and petals reflexed at anthesis. Dorsal sepal linear-elliptic, acuminate, 15–20 × 1.5–2 mm. Lateral sepals similar. Petals narrowly linear-tapering, acuminate, 14–15 × 1–1.5 mm. Lip 3-lobed in the middle, 15–16 × 5–6 mm; side lobes obliquely oblong, truncate, 8–9 × 2–3 mm; midlobe linear-tapering, acuminate, 7–8 mm long; spur pendent, narrowly cylindrical from a narrow mouth, 110–140 mm long. Column 5 mm long, glandular; anther cap giving the tip of the column a hooked appearance; pollinia 2, stipes bifid with linear lobes; viscidium oblong.
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.
Epiphyte or lithophyte on inselberg partly-shaded bare rock surfaces; 1000–1300 m.
Flowers in the rainy season, from December to February.
The species is only recorded from Zimbabwe, namely from the area around the Great Zimbabwe National Monument, which gives the country its name.
ZIMBABWE • Masvingo [Victoria District], Mt Morgenster; 1000 m (3500 ft); fl. in cult. Harare [Salisbury]; 24 Jan. 1956; R.W. Jackson 56814; K!, SRGH • Masvingo, 16 km NW of Ndanga; 29 Dec. 1976; L.J. Mullin in GHS 25198; SRGH!.
The species is given a Red List status of Endangered: EN B1ab(v)+B2ab(v). Ypsilopus zimbabweensis is known from three collections and one observation (https://www.inaturalist.org/observations/143791156) made between 1956 and 2012, representing four occurrences and three locations, including one within the Great Zimbabwe National Monument, a Cultural World Heritage Site. The extent of occurrence (EOO) is 132.1 km2 and the area of occupancy (AOO) is 16 km2. The EOO and AOO fall within the limits of the Endangered (CR) category under subcriteria B1 and B2. Since this species occurs only in three locations and a decline of mature individuals is projected because of illegal collection for the orchid trade, it meets condition b(v) for the EN category.
Ypsilopus amaniensis is to be excluded from Flora Zambesiaca, since all regional occurrences correspond to Y. zimbabweensis, namely the recent records illustrated on the Flora of Zimbabwe website (
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.
We thank the curators and staff of BR, BRLU, K, P, and SRGH for making their collections available and for kindly allowing the authors to use the facilities of their institutions. We thank Andrew Brown for the excellent line drawing of the new species and Patricia van de Ruit for her watercolour, the latter reproduced with permission of Jane Browning, the late John Ball’s sister. We thank Bart Wursten, Guido van Asten, Isobyl la Croix, and Russell Hutton for allowing us to use their photographs of Ypsilopus sect. Barombiella. We are grateful to Nicolas Texier for assisting us with the production of the distribution map. Herbarium visits of the first author were supported by the Belgian Fund for Scientific Research (F.R.S-FNRS). The first author’s PhD research was funded by the Belgian Fund for Research Training in Industry and Agriculture (FRIA) of the F.R.S-FNRS (scholarships F 3/5/5 – FRIA/FC 33848881) and by the Van Buuren-Jaumotte-Demoulin Prize, awarded by the David and Alice Van Buuren Fund. An earlier version of this article is part of J.F.’s PhD thesis entitled ‘Advances in angraecoid orchid systematics in Tropical Africa and Madagascar: new taxa and hypotheses for their diversification’ defended at the Université libre de Bruxelles in 2021. The first author thanks Tariq Stévart and Pierre Meerts for supervising his PhD work. Finally, we are grateful to Benny Bytebier, an anonymous reviewer, and Isabel Larridon for their corrections on an earlier version of this manuscript.