Botanical Journal of the Linnean Society (2001), 137: 99–105. With 6 figures doi:10.1006/bojl.2001.0466, available online at http://www.idealibrary.com on A new Ceropegia species from Yemen, and reconsideration of the status of C. arabica, C. barbigera and C. powysii (Apocynaceae: Asclepiadoideae–Ceropegieae) ULRICH MEVE∗ Lehrstuhl für Pflanzensystematik, Universität Bayreuth, D-95440 Bayreuth, Germany RALPH M. MANGELSDORFF Odenwaldstr. 30, D-60538 Frankfurt am Main, Germany Received September 2000; accepted for publication March 2001 A new species, Ceropegia yemenensis Meve & Mangelsdorff (Asclepiadoideae–Ceropegieae), from the province of Damār in northern Yemen, is described and illustrated. The tiny twiner with fleshy roots shares some characters with C. ahmarensis and C. stenantha from East Africa. Including this new species, the flora of Yemen now contains 11 Ceropegia species. The taxonomic status of the highly variable Arabian stem-succulent twiner Ceropegia arabica is reconsidered. A number of deviating forms have been described as distinct species (e.g. C. powysii and C. barbigera in Africa, C. superba in Arabia), or as varieties under C. arabica. Considering the more recently available material from East Africa which shows typical characters of C. arabica sensu lato and material from Yemen with typical features of C. powysii, C. barbigera is recognized as synomym of C. powysii, and C. powysii is reduced to varietal  2001 The Linnean Society of London rank under C. arabica. ADDITIONAL KEY WORDS: Arabia – Ceropegia ahmarensis – Ceropegia galeata – Ceropegia superba – Ceropegia yemenensis – Ceropegia stenantha – East Africa – taxonomy. foliosa Bruyns, C. rupicola Deflers and C. variegata Decne., were observed in the field. In this area, two unidentified Ceropegia species, Mangelsdorff Y24 and Mangelsdorff Y26, were also found. The single plant of Mangelsdorff Y24 was discovered in the mountains of the Wasāb al’Āli-massif. It carried flower buds which were infested and extensively damaged by larvae of small parasitic wasps, one in each flower, making identification of this Ceropegia impossible. Two cuttings were taken to avoid removing the plant from its site and transported to Germany, where they grew rapidly forming copiously flowering plants. Except for fusiform roots instead of tubers, Mangelsdorff Y24 is vegetatively similar to ‘C. vignaldiana A. Rich.’, the small-leaved form of C. bulbosa Roxb. (cf. Bruyns, 1988; Collenette, 1999), with its linear leaves and thin and wiry stems. The flowers, however, closely resemble those of the well-known and widespread African species C. stenantha K. Schum., INTRODUCTION On a trip from Madı̄nat Aš-Šarq to At-Talūt in the northern part of Yemen in 1998, the second author observed two asclepiads in their natural environment, including Kanahia laniflora Decne., common on the banks of wadis regularly carrying water in the rainy season, Angolluma eremastrum (O. Schwartz) Plowes, A. wissmannii (O. Schwartz) Plowes, Caralluma cicatricosa (Deflers) N.E. Br., C. subulata (Forssk.) Decne., Echidnopsis squamulata (Decne.) P.R.O. Bally, Pergularia daemia (Chiov.) Chiov, P. tomentosa L., Rhytidocaulon macrolobum Lavranos and several additional shrubby and succulent species. In addition, some ceropegiads such as Ceropegia arabica H. Huber, C. aristolochiodes Decne., C. bulbosa Roxb. s.l., C. ∗ Corresponding author. E-mail: ulrich.meve@uni-bayreuth.de 0024–4074/01/090099+07 $35.00/0 99  2001 The Linnean Society of London 100 U. MEVE and R. M. MANGELSDORFF and also the recently described C. ahmarensis Masinde (Masinde, 2000). Nevertheless, coronal and gynostegial structures are different in these three taxa. In its character composition, especially in relation to flower and gynostegium, and in its wiry, non-succulent stems and fusiform succulent roots, Mangelsdorff Y24 represents a unique new species of the Arabian flora. Hence, although the material originates from just a single collection, it is considered a sufficient basis for describing a new species, Ceropegia yemenensis. MATERIAL AND METHODS INVESTIGATED MATERIAL CITED IN THIS STUDY Ceropegia arabica var. arabica: Yemen (N), s. loc., Noltee 2246 (MSUN, UBT); Yemen (N), s. loc., Noltee s.n. sub IPPS 2852 (MSUN). C. arabica var. powysii: Yemen (N), c. 4 km below Markaz Ad-Dan on the Western slopes of the Wasāb Al-‘Alı̄-massif, Mangelsdorff Y26 (UBT); Kenya, Mt Maktau, central heights, Meve 941 (MSUN, UBT); Kenya, Laikipia, Masinde 828 (MSUN). C. arabica var. superba: Yemen (N), 15 km S Souk Gutfan, Mangelsdorff Y19 (UBT); ex hort. Städt. Sukk.Sammlung Zürich, sub Lavranos 28619 (UBT); Saudi Arabia, Jebel Fayfa, Collenette 3159 (ZSS). C. barbigera: Ethiopia, Marda Pass near Jijiga, Lavranos & Gilbert 9241 (K; clonotype material in cult. MSUN). C. yemenensis: Yemen (N), c. 20 km east of Markaz AdDan, Mangelsdorff Y24 (B, FR, UBT). Additional relevant herbarium material from K, EA, BM, WAG, G, S and RIY was also studied. METHODS For morphological comparison, fresh and ethanol-fixed flowers were dissected and analysed under a binocular microscope; details of the flowers were drawn by using a camera lucida. Chromosome numbers were established from adventitious root tip squash preparations. The root tips were pretreated in 0.002 M hydroxyquinoline for 4 h at 20°C (Tjio & Levan, 1950), fixed in Carnoy’s solution for 24 h at 20° and stained with carmine for 24 h at 60°C (Snow, 1963). RESULTS AND DISCUSSION Ceropegia yemenensis Meve & R.M. Mangelsdorff sp. nov. (Figs 1, 2) Affinis C. stenantha K. Schum. sed ramis filo metallico similis, foliis linearibus, 1–2 mm diametro, lobis exterioribus coronae bifidis, deltoideis, ciliatis differt. Type. Yemen, Wasāb al’Āli-massif, c. 20 km east of Markaz Ad-Dan 14°20′N, 43°51′E, cuttings cultivated in greenhouses at Frankfurt and Bayreuth Universities, Germany, flowering at both places in June to Oct. 1999), Mangelsdorff Y24 [B, holotype; FR, UBT, isotypes; isotypes including spirit material]. Description. PLANT a sparsely branched, leafy, nearly glabrous climber up to 50 cm high. Latex clear. ROOTS fusiform, fleshy. STEMS wiry, terete, glabrous, Ζ1 mm diam., green, sometimes showing a maroonish mottling in older stems. LEAVES herbaceous to subsucculent, conduplicate; PETIOLES 1–2 mm long, with fine whitish cilia along rims of adaxial channel, basally with minute ovoid stipular glands, c. 0.8×0.5 mm; lamina 15–90×1–2 mm, linear to very narrowly lanceolate, acute, slightly channelled on top along midrib, prominent beneath, fresh green, margins minutely ciliate. INFLORESCENCE a pseudo-umbellate cyme, 1–2(–5)flowered, flowers opening successively, with fresh fragrance, most strongly emitted around noon; PEDUNCLE 3–10 mm long, 0.5 mm in diam., filiform, horizontal, glabrous; BRACTS minute; PEDICEL c. 10 mm long, 0.5 mm in diam., terete, glabrous. SEPALS 1–2 mm long, 0.5 mm wide near base, subulate-lanceolate, acute, pale green, glabrous. COROLLA 25–35 mm long, slightly curved; tube 17–23 mm long, in basal 1/3 with ovoid inflation, c. 6–9×3–4 mm, at extreme base slightly constricted; tube slightly curved above inflation and narrowing around the middle to c. 1.5 mm diam., cylindrical, moderately dilating into throat of 2–3 mm diam.; exterior of tube in basal half whitish-green, apically passing into pale yellow; interior of inflation purple-red, apically with a ring of white hairs, interior of small part of tube yellowish, glabrous; lones 9–12 mm long, linear-lanceolate, folded back along midrib, except auriculate bases; in folded state c. 1 mm diam., apically fused to form an ovoid cage-like structure, bright yellow all over, glabrous. GYNOSTEGIUM with CORONA sessile, c. 3×3.5 mm, cup-shaped, yellow; interstaminal corona lobes deeply bifid into free deltoid lobules, each lobule c. 0.5×0.5 mm, ascending, acute, yellow with reddish margins, covered with suberect and inward-pointing, whitish-translucent needle-like hairs up to 0.6 mm long; staminal corona lobes c. 2.5×0.4 mm, laterally flattened, incumbent upon anthers, erect, basally glabrous or with few whitishtranslucent needle-like hairs up to 0.6 mm long, apically connivent, glabrous except papillose apices. ANTHERS subquadrate; guide rails strictly vertical, c. 0.45 mm long, 0.1 mm wide along whole length. POLLINARIUM: pollinia ovoid-subrectangular, c. 0.3×0.2 mm, yellow, germination mouths straight, strictly along inner side, slim; corpusculum oblanceolate, c. 0.2 mm long, basally with globoid, lateral, A NEW SPECIES AND A NEW COMBINATION IN CEROPEGIA 101 whitish-translucent projections. CARPELS glabrous. FOLLICLES and SEEDS unknown. Chromosome number. 2n=22 (Voucher: Mangelsdorff Y24, in cult. Univ. Bayreuth). Habitat. The new species was found growing close to a community which is mainly composed of Euphorbia cactus Ehrenb. ex Boiss. and an undetermined shrubby to sub-arborescent spiny Acacia species next to cliffs above terraces. Here, at around 1500 m above sea level on basaltic subsoil, the ground is too steep and rocky to be utilized. This leaves the area in a rather undisturbed condition, and due to the spininess of the Acacia species, it is impenetrable. The single Ceropegia plant was found between the edge of a boulder and this community. It was twining between Euphorbia cactus and Gomphocarpus sinaicus Boiss. Plants growing nearby included Psiadia punctulata (DC.) Vatke (Asteraceae) as a shrubby form with undulate leaf margins, Striga gesnerioides (Willd.) Vatke (Scrophulariaceae), a hemi-parasitic herb infesting Euphorbia cactus, Jatropha variegata Vahl (Euphorbiaceae), and some grass species. The leaves of Ceropegia resembled those of G. sinaicus, and the former is to be found entwined in the latter. Both were well-camouflaged and obviously well-protected against grazing; Gomphocarpus with its sticky, white latex is not grazed. Distribution. Yemen (N), known from the type collection only. Remarks. The main diagnostic features of Ceropegia yemenensis are the thin and wiry stems, linear leaves, one- to few-flowered, pedunculate inflorescences, and the nearly straight corolla with auriculate corolla lobe bases. Distinct gynostegial characters are the cupshaped, sessile corona with bifid interstaminal and laterally compressed staminal corona (Fig. 1). This combination of characters makes C. yemenensis a distinct member of the genus. Other peculiarities are the intense scent of the flowers and the extraordinary small and straight guide rails (Fig. 1D). However, the floral similarities between the new species and C. stenantha, which is distributed from eastern to southern Africa, are striking, most probably due to parallel evolution within the genus. The phenomenon of floral convergence is widespread within the subfamily, and has led to much taxonomic confusion in the past (Meve & Liede, 1999). Vegetative and gynostegial characters as well as (often) coronal characters are much more reliable in Ceropegia (though not necessesarily in other Asclepiadoideae genera!) than shape and coloration of the corolla. Both stem and gynostegium, including the Figure 1. Ceropegia yemenensis sp. nov. A, portion of stem with one leaf; B, flower; C, corona in lateral view; D, guide rails with pollinarium and two anthers; E, pollinarium. All drawn from the type Mangelsdorff Y24 by U. Meve. corona of C. stenantha, do not fit those of C. yemenensis. In C. stenantha the stems are succulent, striate, subquadrate in cross-section and swollen at the nodes; they exude a latex which is slightly ‘milky-cloudy’ (cf. Archer, 1992: XIII), but not clear as in C. yemenensis and in most other ceropegiads. The corona is stipitate with poorly developed, glabrous interstaminal corona ‘lobes’ and slender apically diverging staminal corona lobes (Bruyns, 1984: 24). In addition, the guide rails are broadly deltoid, and the pollinia are ovoid with the germination mouth subapically. Another taxon with similar flowers is the recently described Ceropegia ahmarensis Masinde from Somalia (Masinde, 2000). Its corona is different because it is stipitate; the bifid interstaminal corona lobes are 102 U. MEVE and R. M. MANGELSDORFF conspicuously stiff-hairy outside and the staminal corona is long and spathulate. Again, the vegetative morphology of C. yemenensis is too different to take any conspecifity into consideration, since C. ahmarensis is a stem-succulent twiner with ovate-lanceolate leaves. The true relationships of C. yemenensis therefore remain unresolved. Our new Ceropegia species is the eleventh found on the Arabian Peninsula, and together with C. foliosa Bruyns and C. sepium Deflers is the third endemic restricted to the Yemen (cf. Bruyns, 1988; Wood, 1997). CEROPEGIA ARABICA SENSU LATO The other unidentified Ceropegia species was found at an altitude of about 1600 m a.s.l. below the village of Markaz Ad-Dan on the western slopes of the Wasāb al’Āli-massif. Clusters of tufted shoots were hanging out of crevices in a large, almost vertical boulder. At first sight, the shoots could be taken for a Sarcostemma species or Cynanchum gerrardii (Harv.) Liede. However, the more slender stems exuding clear latex revealed their true affinity. Similar looking plants were seen nearby growing inaccessibly in the cliffs close to plants of Euphorbia ammak Schweinf. This Yemeni Ceropegia (Mangelsdorff Y26) with fusiform-fleshy roots vegetatively resembles taxa like C. arabica H. Huber, the South African C. fimbriata K. Schum. or the Indian C. juncea Roxb. They all share succulent, twining, striate and slightly rough stems with acute short-lived leaf rudiments. Three species of this natural genus subgroup, C. arabica, C. subaphylla K. Schum (syn. C. botrys K. Schum.) and C. tihamana Chaudhary & Lavranos (Bruyns, 1988; Wood, 1997; Meve, in press) are distributed in Arabia. However, while most of these species possess fleshy-fusiform roots, C. subaphylla and C. tihamana have root tubers. The flowers of Mangelsdorff Y26 do not fit immediately into any of the three species of the subgroup described for Arabia, because of their geniculate corolla tube and their corolla lobes being slightly keeled and apically blunt, creamy-reddish and crowned by a tuft of vibratile, purple hairs (Figs 3, 4, 6C). However, a close examination, especially of the corona (Fig. 6A), revealed that Mangelsdorff Y26 nevertheless belongs to the C. arabica complex, although it represents a form that has not hitherto been seen in Arabia. In particular, the blunt corolla lobes are reminiscent of C. arabica var. abbreviata Bruyns, a variety restricted to Saudi Arabia (cf. Bruyns, 1988). Unexpectedly, however, the flowers mostly resemble those of the East African taxon Ceropegia powysii D.V. Field (Figs 5, 6D–F). This points to a much more complex systematic situation as argued by D.V. Field (1982) when describing C. powysii, or by Bruyns (1989), when describing another closely related taxon of Kenya, Ethiopia and Somalia, C. barbigera Bruyns. The blunt cream-reddish coloured tips of the corolla lobes (of Mangelsdorff Y26), crowned or lined by vibratile hairs, are diagnostic of C. powysii (Masinde 828 represents such a form very close to the type of C. powysii, see Figs 5, 6D–F). The general shape and coloration of the corolla are especially similar to flowers of C. powysii from southern Kenya (cf. Meve 941). Apart from difference in size, it is mainly the rounded base of the corolla lobes in Mangelsdorff Y26 that is similar to those usually found in C. arabica var. arabica (cf. Fig. 4). In typical C. powysii the corolla lobes tend to be affixed to the tube in a rather acute-angled manner. This leads to the unhappy situation that Mangelsdorff Y26 can be most satisfactorily attributed to Arabian taxa like C. arabica although overall similarity is closer to the Kenyan C. powysii. For example, there is no significant difference between Mangelsdorff Y26 and Archer 8/346 from Kenya (see Archer, 1992: XVIII). Such judgement underlines the necessity for verification of the status of all taxa within this complex. Archer (1992) in his Kenya Ceropegia Scrapbook depicted a wide array of flowers belonging to the C. arabica s.l. complex (cf. Archer’s ‘species’ XVI, XVII; Masinde, 1998). Although these elements remained unnamed in the book, Archer nevertheless perfectly portrayed the wide variability of corolla shape in the C. powysii/arabica complex in Kenya. It seems that every single population or even individual expresses another form regarding flower shape and size, length, width and hairiness of corolla lobes, coloration etc. Archer’s Nos 6/301 and 8/346 should be classified as C. powysii (sensu Field, 1982), while No 2/23 could be classified as the Arabian C. arabica var. superba (cf. Bruyns, 1988: 317). Nos 1/22 and 4/165 even look like a mixture of C. arabica var. superba and var. abbreviata (cf. Bruyns, 1988: 319). Finally, a form identifiable as C. barbigera, which is documented here for Kenya for the first time (Archer’s field No 9/347; see also Masinde, 1998), is more similar to C. powysii than to the type collection from Somalia (cf. Bruyns, 1989). It is only the very short staminal corona lobe in the type of C. powysii (cf. Field, 1982: fig. 2C), which is deviant. However, since long and erect staminal corona lobes, as typical for C. arabica and C. barbigera, have also been found in different collections of C. powysii also (Fig. 6D), this character is of very questionable value in the complex. From the karyological point of view there is evidence that the differentiation within the complex might be forced by genome size evolution. While C. arabica var. arabica s.s. (IPPS 2852, Noltee 2264), C. powysii s.s. (Meve 941, Masinde 828) and also C. barbigera (clonotype) have been found to be diploid with 2n=22 (Meve & Masinde, unpubl. data), the two plants of C. arabica A NEW SPECIES AND A NEW COMBINATION IN CEROPEGIA 103 Figures 2–5. Fig. 2. Ceropegia yemenensis sp. nov. (Mangelsdorff Y24, type plant). Fig. 3. Ceropegia arabica s.l. (Mangelsdorff Y26). Fig. 4. Ceropegia arabica s.s. (IPPS 2852). Fig. 5. Ceropegia arabica var. powysii (Masinde 828). Figs 2–4 by U. Meve, Fig. 5 by P. S. Masinde. var. superba investigated so far (Mangelsdorff Y19, Collenette 3159), and Ceropegia ‘Mangelsdorff Y26’ from the Wasāb al’Āli-massif, showed a tetraploid genome of 2n=44 (Meve, unpubl.). However, more material, incl. C. arabica var. abbreviata, needs to be investigated to support the hypothesis of karyological differentiation within this complex. The easiest solution of the problem would be the lumping of all taxa into a single species, C. arabica, characterized predominantly by a common habit and 104 U. MEVE and R. M. MANGELSDORFF Figure 6. A–C, Ceropegia arabica s.l. A, corona in lateral view; B, pollinarium; C, vibratile clavate hair of tip of corolla lobe. D–F, Ceropegia arabica var. powysii. D, corona in lateral view (corona slightly shrunken by ethanol fixation); E, pollinarium; F, vibratile clavate hair of tip of corolla lobe. All drawn by U. Meve, A–C, from Mangelsdorff Y26, D–F from Meve 941 (slightly shrunken by ethanol fixation). corona shape (Fig. 6A, D). To our understanding this would also be the most adequate treatment when applying a ‘biospecies concept’ (cf. Mayr, 1969). However, with regard to morphology as well as geographical distribution, differentiaton into different forms or varieties cannot be questioned and should be expressed by appropriate taxa, although clear morphological demarcation between all the taxa involved is impossible because of an extraordinary diversity with many intermediate forms. It is only the typical C. arabica var. arabica, characterized by long, small and twisted corolla lobes, which has not yet been found on the African mainland. Thereby, only a geographical demarcation is clearly present. Bruyns (1988) recognized Ceropegia arabica vars. arabica, abbreviata and suberba on the Arabian Peninsula, and distinguished them by corolla lobe morphology only. Since the three varieties occur sympatrically and even together at core localities such as the Jabal Fayfa in southern Saudi Arabia, a varietal rank seems to be unsuitable: treatment as forms rather than varieties would appear to be appropriate (cf. Stuessy, 1990: tab. 12.1). The polymorphism within C. arabica is highly comparable to that found in the pan-African leaf and stem succulent twiner C. nilotica Kotschy (cf. Archer, 1992: XX, XXI), where many (synonymous) names are in use, although they are insufficient to describe all the forms and variants found so far. Again, common leaf, stem and ‘core’ corolla morphology characterizes the ‘biospecies’ C. nilotica quite satisfactorily. Other taxa around the C. arabica complex are the East African C. barbigera (Bruyns, 1989) and C. galeata H. Huber (cf. Dyer, 1965; Archer, 1992: XVI). C. barbigera, of which only a few collections are known from Kenya, Somalia and Ethiopia, should be included in C. arabica. Even though C. barbigera seems to represent a special morphotype characterized by blunt corolla lobes, its maintenance as a distinct species would result in an unbalanced treatment since many other ‘forms’ within C. powysii would remain taxonomically unresolved, and there is clearly a cline of forms between C. powysii and C. arabica. This latter problem has also been recognized by the author of C. barbigera, a species which was described from two specimens, when it was noted that there is a collection from Somalia in K, Bally 11111, which “is intermediate between C. barbigera and C. arabica” (Bruyns, 1989: 723). C. galeata, in contrast, is better kept distinct at the moment, because it seems fairly well characterized by the ‘helmet’ formed by the corolla lobes, the (often) laterally compressed staminal corona lobes and very shortly bifid interstaminal ones (cf. Dyer, 1965). However, this taxon is poorly known and has been collected only a few times in southeastern Kenya. The Arabian C. subaphylla (=C. botrys), similar in stem, leaf and corona shape, is kept separate because of its single root tuber and characteristic and constant shape of the corolla tube. Interestingly, C. subaphylla, and additional species such as C. aristolochioides Decne., C. somalensis Chiov. and C. variegata Decne. are distributed in East Africa as well as in south-west Arabia (Bruyns, 1988; Meve, in press), pointing to a parallel evolutionary history of these species with C. arabica. In conclusion, the systematic situation within the C. arabica complex might be best reflected by reducing C. powysii to varietal rank under C. arabica, and adopting a concept with regard to geographical distribution. Thus, all African collections of the complex should be named C. arabica var. powysii. Stuessy (1990: Tab. 12.1) in his ‘rules’ for distinguishing subspecies, varieties and forms recommended subspecific rank, when strictly allopatric distribution is shown. A NEW SPECIES AND A NEW COMBINATION IN CEROPEGIA However, the conspicuous morphological distinctions he also encouraged when installing subspecific taxa are lacking. The varietal category, which is already in use in C. arabica, therefore seems to be appropriate. The new treatment as proposed here agrees with Masinde (1998), who confined all collections depicted in Archer (1992) under XVII and XVIII as C. powysii. However, in the case of such single collections as that of Mangelsdorff Y26, it still remains a matter of personal taste and weighting of the characters in naming a specific plant, e.g. Archer 2/23 (Archer 1992: XVII) as C. arabica var. superba or as C. arabica var. powysii, and Mangelsdorff Y26 as C. arabica var. arabica, C. arabica var. powysii, or in consideration of its tetraploid genome, C. arabica var. superba. Discussion on flower morphological features as well as on ploidy levels which underly the delimitation of varieties (and forms), is needed to decide whether or not the maintenance of infraspecific levels within C. arabica is taxonomically justified. Ceropegia arabica H. Huber var. Powysii (D.V. Field) Meve & R.M. Mangelsdorff comb. et stat. nov. Basionym. Ceropegia powysii D.V. Field, Kew Bull. 37: 308 (1982). Type. Kenya, Laikipia, Lower Narok Farm, Field & Powys 115 [K]. =Ceropegia barbigera Bruyns, Kew Bull. 44: 721 (1989), syn. nov. Type. Ethiopia, Marda Pass near Jijiga, Lavranos & Gilbert 9241 [K]. Detailed descriptions and illustrations of the varieties and forms included in C. arabica are published in Archer (1992), Bruyns (1988, 1989), Collenette (1991, 1999) and Field (1982). ACKNOWLEDGEMENTS We thank Dr P. Siro Masinde, East African Museum, Nairobi, for placing different sketches of C. stenantha at our disposal and providing Figure 5. 105 REFERENCES Archer PG. 1992. Kenya Ceropegia Scrapbook. Hobart (Australia): Artemis. Bruyns PV. 1984. Ceropegia, Brachystelma and Tenaris in South West Africa. Dinteria 17: 3–80. Bruyns PV. 1988. Studies of the Flora of Arabia XXIV: The genus Ceropegia in Arabia. Notes Royal Botanic Garden Edinburgh 45: 287–326. Bruyns PV. 1989. Two new species of Ceropegia (Asclepiadaceae-Stapelieae). Kew Bulletin 44: 721–726. Collenette S. 1991. Ceropegias in Saudi Arabia. Kew Magazine 8(1): 24–37. Collenette S. 1999. The ceropegias in Saudi Arabia. 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