Research Article
Research Article
A new Ypsilopus (Orchidaceae, Angraecinae) from Zimbabwe and notes on the parallel evolution of extreme column exsertion in African angraecoids
expand article infoJoão Farminhão§, Phillip J. Cribb|
‡ Universidade de Coimbra, Coimbra, Portugal
§ Université libre de Bruxelles, Brussels, Belgium
| Royal Botanic Gardens, Richmond, United Kingdom
Open Access


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 resultsYpsilopus 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 gracillimaA. 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 (Armbruster and Muchhala 2009), notably in Orchidaceae (e.g. Dressler 1968; Nilsson et al. 1987). Column exsertion is one of the characters associated with the evolution of these shifts, as observed in Stylidiaceae (Armbruster et al. 1994) and Campanulaceae (Muchhala and Potts 2007; Muchhala 2008), but its importance in orchids remains undocumented.

A preliminary review of hawkmoth pollination in angraecoid orchids (Farminhão 2021), identified two clades of African species that possibly illustrate how column exsertion leads to shifts of pollen attachment sites in species sharing large hawkmoths as pollinators. In the Guineo-Congolian region, Aerangis gracillima (Kraenzl.) J.C.Arends & J.Stewart presents a column attaining more than double the length of those of closely-allied Aerangis stelligera Summerh. and A. bouarensis Chiron. Similarly, in eastern and southeastern Africa, and with a more sizeable difference, Ypsilopus schliebenii (Mansf.) D’haijère & Stévart bears a column four to approximately five times longer than sister Y. amaniensis (Kraenzl.) D’haijère & Stévart. The striking resemblance in column elongation of A. gracillima and Y. schliebenii led taxonomists to class both species in the now defunct genus Barombia Schltr. (Schlechter 1914; Cribb 1980), which was revealed to be polyphyletic by molecular phylogenetics (Simo-Droissart et al. 2018; D’haijère et al. 2019; Farminhão et al. 2020).

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. (D’haijère et al. 2019, 2021; Farminhão et al. 2021). Ypsilopus schliebenii and Y. amaniensis are the only representatives of Ypsilopus sect. Barombiella (Szlach.) D’haijère & Stévart, which were formerly classified within polyphyletic Rangaeris (Farminhão et al. 2020). The well-known Y. amaniensis is widespread in East Africa from Eritrea and Ethiopia south to Tanzania (Cribb 1989; Demissew et al. 2004). It is also reported from Zimbabwe, amongst others, by Ball (1978) and la Croix and Cribb (1998). However, the three collections (viz. Ball 1394, Jackson 56814, Mullin in GHS 25198) we have examined from there differ significantly from the East African ones, enough to consider them to belong to a distinct, albeit closely allied species which we describe here.

Material and methods

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 (Cribb 1989; Geerinck 1992; la Croix and Cribb 1998; Szlachetko and Olsweski 2001). Body measurements of Xanthopan morganii (Walker, 1856), the largest hawkmoth from Tropical Africa, were estimated using ImageJ v.1.52d (Schneider et al. 2012) based on forewing length and iconography provided by Minet et al. (2021).

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 Thiers 2023). Based on newly collected data, we update the key to the sections of Ypsilopus, with a focus on Ypsilopus sect Barombiella, presented by D’haijère et al. (2019, 2021). Distribution records and photographs of species in Y. sect. Barombiella were mined from social media, namely iNaturalist, Facebook, and Flickr, and used to complete the description, phenology, and range of the species.

IUCN Red List categories and criteria (IUCN 2022) were applied to evaluate the conservation status of the new species. The number of “locations” (sensu IUCN 2022) was calculated considering the type of threats, such that a single “location” may include more than one adjacent occurrence. The Extent of Occurrence (EOO) and Area of Occupancy (AOO) were calculated using GeoCAT (Bachman et al. 2011) on georeferenced specimen data. The AOO was calculated based on a 2 × 2 km grid cell size.


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. 1). There is at least one contact zone between A. gracillima and A. stelligera in southern Cameroon, while species in Y. sect. Barombiella are separated by large geographical gaps: ca 200 km and 800 km separate Y. schliebenii from the closest populations of Y. amaniensis to the north and south of its range, respectively. The population of Y. zimbabweensis, newly described here, is separated by a gap of more than 1,200 km from the southernmost occurrence of Y. amaniensis in the Rubeho and Uluguru Mountains in Tanzania.

Figure 1. 

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 1.

Table 1.

Spur and column lengths in the Aerangis gracillimaA. 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 (Droissart et al. 2018): in the Guineo-Congolian region, A. gracillima is confined to Lower Guinea, while sister A. stelligera is more widespread in Lower Guinea and Congolia; in Eastern Africa, the range of Y. schliebenii is centred in the Southern Rift montane region, whereas Y. amaniensis is more widespread in Central Tanzania and East African montane regions, with the isolated population of Y. zimbabweensis included in the South Zambesian. The geographical pattern of column length distribution suggests that column exsertion may have been reinforced after secondary contact in a scenario of allopatric/peripatric speciation in both angraecoid clades (Farminhão 2021).

Considering spur length (see Johnson et al. 2017) and field observations (Martins and Johnson 2013; Balducci et al. 2019), it is likely that the Aerangis gracillimaA. stelligera clade and Ypsilopus sect. Barombiella share some large sphingid species as their exclusive pollinators, namely Agrius convolvuli (Linnaeus, 1758), Coelonia fulvinotata (Butler, 1875), and/or Xanthopan morganii. It is hypothesised that the pollinia attachment site shifted from the head to the dorsal region of the thorax (Fig. 1), based on the head-thorax length of 1.9 cm in Xanthopan morganii, mirroring the gap in column exsertion (see Table 1). The use of camera traps optimised for studying plant-insect interactions (e.g. Droissart et al. 2021) will be instrumental to test these hypotheses, notably near the contact zones between sister species.

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 (Mapaura 2002), and it is one of the five angiosperms restricted to the inselbergs of Zimbabwe (Seine et al. 1998; Mapaura 2002), the others being Craterostigma syncerus (Seine, Eb.Fisch. & Barthlott) Eb.Fisch., Schäferh. & Kai Müll., Delosperma steytlerae L.Bolus, Kalanchoe wildii Raym.-Hamet ex R.Fern., and Portulaca rhodesiana R.A.Dyer. The number of species in Y. sect. Barombiella, thus, rises to three, all presenting non-overlapping latitudinal distributions in Tropical Africa.

Taxonomic treatment

Key to Ypsilopus

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 D’haijère et al. 2021)
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.

Ypsilopus zimbabweensis Farminhão & P.J.Cribb, sp. nov.

Figs 1, 2, 3, 4


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. 1).


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.

Additional material (paratypes)

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!.

Preliminary IUCN conservation assessment

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 ( 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 (Hyde et al. 2023). Specimens identified as Angraecum sp. in the inselbergs of Zimbabwe (Seine et al. 1998) are also possibly ascribable to Y. zimbabweensis. Patricia van de Ruit’s fine watercolour illustration of this species (as Rangaeris amaniensis) is reproduced here (Fig. 3). Iconography produced by the same artist, for the same book, was instrumental to the description of another new orchid from Zimbabwe (Farminhão and Cribb 2020). The new species is also illustrated here with a line drawing by Andrew Brown (Fig. 2) and a photograph in la Croix and la Croix (1997), reproduced here (Fig. 3). The novelty has been widely cultivated and misidentified as Rangaeris amaniensis by hobbyists in Zimbabwe, South Africa, Australia, and Europe.

Figure 2. 

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.

Figure 3. 

Watercolour of Ypsilopus zimbabweensis, originally identified as Rangaeris amaniensis, by Patricia van de Ruit, published in Ball (1978: 1394). Reproduced with permission.

Figure 4. 

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).


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.


  • Armbruster WS, Edwards ME, Debevec EM (1994) Floral character displacement generates assemblage structure of Western Australian triggerplants (Stylidium). Ecology 75: 315–329.
  • Armbruster WS, Muchhala N (2009) Associations between floral specialization and species diversity: cause, effect, or correlation? Evolutionary Ecology 23: 159–179.
  • Bachman S, Moat J, Hill AW, De La Torre J, Scott B (2011) Supporting Red List threat assessments with GeoCAT: geospatial conservation assessment tool. ZooKeys 150: 117–126.
  • Balducci MG, Martins DJ, Johnson SD (2019) Pollination of the long-spurred African terrestrial orchid Bonatea steudneri by long-tongued hawkmoths, notably Xanthopan morganii. Plant Systematics and Evolution 305: 765–775.
  • Ball JS (1978) Southern African Epiphytic Orchids. Conservation Press (Pty) Ltd, Johannesburg & London, 1–247.
  • Cribb PJ (1980) Barombia schliebenii – an extraordinary epiphytic orchid from central Tanzania. South African Orchid Journal 11: 110.
  • Cribb PJ (1989) Rangaeris. In: Polhill R (Ed.) Flora of Tropical East Africa. Orchidaceae (Part 3). A.A. Balkema, Rotterdam, 570–573.
  • Demissew S, Cribb P, Rasmussen FN (2004) Field Guide to Ethiopian Orchids. Royal Botanic Gardens, Kew, Richmond, 1–304.
  • D’haijère T, Mardulyn P, Dong L, Plunkett GM, Simo-Droissart M, Droissart V, Stévart T (2019) Molecular phylogeny and taxonomic synopsis of the angraecoid genus Ypsilopus (Orchidaceae, Vandeae). Taxon 68: 455–470.
  • D’haijère T, Farminhão JNM, Stévart T, Fischer E (2021) Novelties among East African angraecoids (Orchidaceae, Angraecinae). Nordic Journal of Botany 39: e03184.
  • Droissart V, Dauby G, Hardy OJ, Deblauwe V, Harris DJ, Janssens S, Mackinder BA, Blach-Overgaard A, Sonké B, Sosef MM, Stévart T, Svenning J-C, Wieringa JJ, Couvreur TL (2018) Beyond trees: biogeographical regionalization of tropical Africa. Journal of Biogeography 45: 1153–1167.
  • Droissart V, Azandi L, Onguene ER, Savignac M, Smith TB, Deblauwe V (2021) PICT: a low‐cost, modular, open‐source camera trap system to study plant–insect interactions. Methods in Ecology and Evolution 12: 1389–1396.
  • Farminhão J (2021) Advances in angraecoid orchid systematics in Tropical Africa and Madagascar: new taxa and hypotheses for their diversification. PhD Thesis, Université libre de Bruxelles, Belgium.
  • Farminhão JNM, D’haijère T, Droissart V, Dumbo Isonga L, Dong L, Verlynde S, Plunkett GM, Simo-Droissart M, Stévart T (2020) An elegy to Rangaeris, including a description of two new genera in the Cyrtorchis-Tridactyle clade (Orchidaceae, Angraecinae). Annals of the Missouri Botanical Garden 105: 300–322.
  • Farminhão JNM, Verlynde S, Kaymak E, Droissart V, Simo-Droissart M, Collobert G, Martos F, Stévart T (2021) Rapid radiation of angraecoids (Orchidaceae, Angraecinae) in Tropical Africa characterised by multiple karyotypic shifts under major environmental instability. Molecular Phylogenetics and Evolution: 107105.
  • Geerinck D (1992) Flore d’Afrique Centrale (Zaïre–Rwanda–Burundi): Spermatophytes; Orchidaceae (seconde partie). Jardin Botanique National de Belgique, Meise, 297–780.
  • Johnson SD, Moré M, Amorim FW, Haber WA, Frankie GW, Stanley DA, Cocucci AA, Raguso RA (2017) The long and the short of it: a global analysis of hawkmoth pollination niches and interaction networks. Functional Ecology 31: 101–115.
  • la Croix I, Cribb PJ (1998) Rangaeris. In: Pope G (Ed.) Flora Zambesiaca 11(2). Orchidaceae. Royal Botanic Gardens, Kew & Flora Zambesiaca Managing Committee, London, 438–442.
  • la Croix I, la Croix E (1997) African Orchids in the Wild and in Cultivation. Timber Press, Portland, Oregon, 1–379.
  • Martins DJ, Johnson SD (2013) Interactions between hawkmoths and flowering plants in East Africa: polyphagy and evolutionary specialization in an ecological context. Biological Journal of the Linnean Society 110: 199–213.
  • Minet J, Basquin P, Haxaire J, Lees DC, Rougerie R (2021) A new taxonomic status for Darwin’s “predicted” pollinator: Xanthopan praedicta stat. nov. Antenor 8: 69–86.
  • Muchhala N, Potts MD (2007) Character displacement among bat-pollinated flowers of the genus Burmeistera: analysis of mechanism, process and pattern. Proceedings of the Royal Society B 274: 2731–2737.
  • Nilsson LA, Johnsson L, Ralison L, Randrianjohany E (1987) Angraecoid orchids and hawkmoths in central Madagascar: specialized pollination systems and generalist foragers. Biotropica 19: 310–318.
  • Simo-Droissart M, Plunkett GM, Droissart V, Edwards MB, Farminhão JNM, Ječmenica V, D’haijère T, Lowry II PP, Sonké B, Micheneau C, Carlsward BS, Azandi L, Verlynde S, Hardy OJ, Martos F, Bytebier B, Fischer E, Stévart T (2018) New phylogenetic insights toward developing a natural generic classification of African angraecoid orchids (Vandeae, Orchidaceae). Molecular Phylogenetics and Evolution 126: 241–249.
  • Szlachetko DL, Olszewski TS (2001) Orchidacées 3. In: Achoundong G, Morat P (Eds) Flore du Cameroun 36. Ministère de la Recherche Scientifique et Technique, Yaoundé, 666–948.
  • Thiers B (2023) Index Herbariorum: a global directory of public herbaria and associated staff. New York Botanical Garden’s Virtual Herbarium. [accessed 27.09.2023]
login to comment