Taxonomy of Vincetoxicum s.str. (Asclepiadoideae, Apocynaceae) from southern Asia including three new species and resurrected names

Abstract This paper presents a taxonomic study of genus Vincetoxicum s.str. from southern Asia. Eleven regional endemic species are recognized on the basis of herbarium studies and fieldwork. Three new species are described: V. lenifoliumsp. nov. (endemic to Pakistan), V. stewartianumsp. nov. (endemic to India), and V. subcanescenssp. nov. (endemic to Pakistan, Kashmir and Tibet). Three species names, V. cabulicum, V. glaucum and V. kenouriense, previously treated as synonyms of V. glaucum, V. canescens and V. hirundinaria, respectively, are resurrected. A neotype is designated for the Afghani endemic V. cabulicum. A lectotype is chosen from the syntypes of V. glaucum. We resolve the long-standing taxonomic problems in three species complexes: V. arnottianum, V. luridum, V. sakesarense, and V. stocksii; V. glaucum, V. canescens and V. cabulicum; and V. hirundinaria and V. kenouriense. Geo-taxonomic distinctions of southern Asian taxa are highlighted by excluding from henceforth the long misrecognized western Eurasian taxa V. canescens and V. hirundinaria. Furthermore, a detailed account of the genus including illustrations of whole plants, leaves and corona, distribution maps, a taxonomic key, morphological descriptions, synonymy, notes, and information on phenology, distribution and habitats is provided. Finally, provisional conservation assessments are provided, which indicate that V. cardiostephanum and V. sakesarense are critically endangered.


Introduction
The subtribe Tylophorinae K. Schum. of Asclepiadoideae, Apocynaceae, comprises the genera Pentatropis R.Br. ex Wight & Arnott with five species, and Vincetoxicum Wolf with approximately 200 species. Liede-Schumann et al. (2012) expanded Vincetoxicum to include Biondia Schlechter, Blyttia Arnott, Diplostigma K. Schumann, Goydera Liede, Pleurostelma Baillon, Rhyncharrhena Mueller, and Tylophora R. Brown. The resulting new combinations, new names and typifications were recently published in Liede-Schumann and Meve (2018). Members of Vincetoxicum are distributed in Africa, Arabia, Australia and Eurasia. The plants are either erect undershrubs or twiners, often with transparent latex, leaves are simple and opposite, and flowers are mostly small with staminal corona lobes and round pollinia. The infra-generic taxa are often difficult to identify. The most important characters for identification are usually confined to the small (± 5 mm long) flowers. The key floral characters include color, dimensions, and internal indumentum of the corolla lobes, and shape, orientation and size of the corona lobes. The vegetative morphological features are often strikingly homomorphic among closely related species.
The revision of Pakistani Vincetoxicum (Ali and Khatoon 1982) was the first detailed study on this group from southern Asia. The authors recognized six species from Pakistan including V. hirundinaria and V. canescens. These two species were recognized in a broader sense, merging Rechinger's V. glaucum into the latter. According to Ali and Khatoon (1982), these two species have a wide range from southern Asia westwards to the Mediterranean region (V. canescens) and Europe (V. hirundinaria). In a phylogenetic analysis, Liede-Schumann et al. (2016) recently recognized the Pakistani specimens as V. glaucum and distinguished them from V. canescens. The former came out as a member of the Western Himalayan subclade while V. canescens was grouped in a small Mediterranean subclade with V. creticum Browicz and V. tmoleum Boissier. The phylogenetic analysis of Liede-Schumann et al. (2016) disintegrated the V. canescens complex into the Mediterranean (V. canescens) and western Himalayan (V. glaucum) entities. Despite these advancements, to solve the V. glaucum complex, which includes plants of the so-called V. cabulicum from Afghanistan and V. glaucum from Pakistan, Kashmir, Tibet (China), India and Nepal, an inclusive taxonomic analysis is needed. Similarly, V. hirundinaria has traditionally been regarded as a variable species and spans a wide range in European Russia, Western Siberia, Turkey, the Caucasus, Kashmir, Pakistan (Hazara, Waziristan) and the Himalayas up to Sikkim (Ali 1983). Southern Asian accessions of V. hirundinaria were lacking in Liede-Schumann et al. (2016). Therefore, a comparison of accessions of V. hirundinaria throughout its range is necessary. More recently, Shah et al. (2018) elucidated the long-misunderstood complex of closely related, purple-flowered species V. arnottianum, V. sakesarense Ali & Khatoon and V. stocksii Ali & Khatoon, which resulted in the addition of a new species V. luridum Stocks ex S.A. Shah that is endemic to Balochistan (Pakistan).
This research revises Vincetoxicum s.str. from southern Asia. Prior to this study, a total of seven Vincetoxicum s.str. species were recognized in southern Asia viz., V. arnottianum (Pakistan, Kashmir and India), V. cardiostephanum (Afghanistan and Kurram valley of Pakistan), V. glaucum (Nepal westwards to Afghanistan), V. hirundinaria (Nepal westwards to Pakistan), V. luridum (endemic to Pakistan), V. sakesarense (endemic to Pakistan) and V. stocksii (endemic to Pakistan). In comparison to previous studies, we recognize 11 Vincetoxicum s.str. species in southern Asia (Table 1). We describe three new species and modify previously existing descriptions. Vincetoxicum luridum was published just recently by Shah et al. (2018), so its description is not repeated in this paper. All species recognized in this treatment are endemic to southern Asia. The long misapplied species names V. canescens and V. hirundinaria are hereby excluded from southern Asia which breaks the connections between the southern Asian and the rest of the Eurasian, especially the western Eurasian, Vincetoxicum species.

Materials and methods
We morphologically examined approximately 800 herbarium specimens, including our recent collections (2015-17) from Pakistan. We conducted a total of 65 field visits to cover Himalaya, Hindukush, and Sulaiman, representing the major mountain ranges of Pakistan ( Fig. 1) and extending into Afghanistan and India. We collected specimens in flowering and fruiting stages for improved characterization. We conserved live plants of V. arnottianum, V. cardiostephanum, V. kenouriense, V. lenifolium, V. luridum, V. sakesarense, V. stocksii and V. subcanescens at the Botanical Conservatory, National Agriculture Research Centre (NARC); Islamabad, Pakistan, for morphological observations and future research. We deposited our fresh collections including the type specimens in RAW and US. We used the live plants for determination of shape and dimensions of smaller structures including corona, gynostegium and calycine colleters. Colors of corollas, fruits, etc., are described from live material or herbarium labels. We carried out morphological examinations at HUP, ISL, KUH, PPFI, PMNH, RAW, and US and received herbarium loans from B, BM, GH, GOET, K, MO, and NY at US. We also retrieved digitized herbarium specimens from the databases JS-TOR Global Plants (https://plants.jstor.org/), E, and P and used either the website's measurement system or IMAGEJ for the downloaded images. Herbarium acronyms follow Thiers (2020). We studied the type specimens of the previously known names V. arnottianum, V. canescens, V. hirundinaria, V. kenouriense, V. sakesarense, V. stocksii, and V. glaucum. The type specimen of V. cabulicum was destroyed in B during World War II, therefore, we studied other specimens from the same area and designated a neotype. We followed the terminology of Ali and Khatoon (1982) for floral characters, and Harris and Harris (1994) for general morphological characters. For illustrations of the whole plant, we mostly used fresh plants and sometimes herbarium specimens. We also illustrated the leaf outlines mainly from fresh plants. During illustrations of corona types, we ensured the best angles that help determine the accurate shape of corona lobes and their orientation. We assessed the conservation status following the IUCN Red List Categories and Criteria (IUCN 2019) using the GIS-based method of Moat (2007) as implemented in the online assessment tool GeoCat (http://geocat.kew.org). The Extent of Occurrence (EOO) measures the range of the species, and the Area of Occupancy (AOO) represents the number of occupied points within that range based on the default grid size of 2 km 2 .
General description of southern Asian Vincetoxicum s.str.

Description of vegetative parts
South Asian Vincetoxicum s.str. species are mostly found in mountains predominantly at higher elevations ranging from 750 to 3650 m. The plants are perennial, growing one to several stems from the rhizomatous base in spring and becoming dormant in winter. They lack milky latex and have clear latex instead. Stems are mostly longitudinally striate and pubescent all around or along one to two lines. Multiple patterns of pubescence are often found in the same species. Pubescence may be dense or sparse depending on the species. Trichomes are exclusively uniseriate, 3-5 celled, falcate or straight, with the terminal cell sometimes inflated. The phyllotaxis is opposite and decussate. However, some plants exhibit leaves in whorls or pseudo-whorls of 3-6 leaves. Laminae are discolorous and of different shapes ranging from linear to broadly ovate. Margins are always smooth. The shape of the apex and base vary depending upon the species. Laminae of the purple-flowered Vincetoxicum species are conduplicate. The adaxial veins, especially the midrib, are pubescent in most taxa. A cluster of small glandular structures, called colleters, are found at the bases of the laminae on the adaxial surface. Depending on the species, the remainder of foliar veins and surfaces are either glabrous or variously hairy. Foliar trichomes resemble those on the stems. Flowers are typically clustered in dense pseudo-umbels either sessile or sub-sessile or both. The pubescence on peduncles is identical to that of the stem in density, but that of the pedicels is often different.

Description of reproductive parts
The sepals are fused basally into a short calyx tube and the calyx lobes are usually adpressed to the corolla. The corolla forms a short, usually glabrous tube. The corolla lobes are either green, whitish green, purple or purple in the lower half and green up to the apex. They are either free from each other to the apex or twisted clockwise up to the apices that enclose the internal parts (in V. arnottianum and V. sakesarense only). Inside, the corolla lobes are either variously pubescent or glabrous; rarely, the trichomes are caducous. The corona is composed of five lobes basally attached to the stamens, hence called staminal corona. The corona is mostly prominent and separate from the stamens except at the base. It is the most important structure from a taxonomic point of view. However, it is difficult to study because of its small size, usually less than one millimeter in dimension. Mostly, it is fleshy and loses water content during herbarium pressing, which somewhat alters the shape and size of the lobes. Studying dried as well as fresh and/or rehydrated flowers is the most precise way of determining the shape and size of corona lobes. Another important character is the length ratio of gynostegium and corona lobes. The gynostegium possesses pollinaria in the anther locules. Each locule possesses one pollinium. The orientation of pollinaria should be noted during dissection of flowers.
The fruit is a typical asclepiad follicle. The two ovaries, if successfully pollinated, develop into paired follicles. The follicles are fused at the base, but diverge at various degrees. Each follicle contains 10-25 seeds attached to a central axis. Seeds are dispersed by wind with the help of a coma, i.e. a tuft of approximately 2-3 cm long white hairs attached to the seed apex. Margins of seeds (wings) are thin all around except at the apex.

Taxonomic treatment
Southern Asian Vincetoxicum s.str.

Distribution and habitat.
Based on the number of past collections and our field observations, this is the most commonly occurring species of Vincetoxicum in southern Asia. It is strictly western Himalayan in distribution and found in India (Himachal Pradesh), Kashmir and Pakistan (Azad Jammu, Kashmir and Hazara Division). It is a deep rooted plant with a thick root stock found on open, sunny mountain slopes in association with grasses or other herbaceous flora. Its elevation ranges from 750 to 2800 m.
Phenology. Flowering from April to September and fruiting from May to October. Provisional conservation status. Near threatened (Table 1). Vincetoxicum arnottianum is found in highly clumped and distant populations. Its populations have been mostly found in areas less than 100 m 2 in size and consist of less than 100 plants.
Notes. Vincetoxicum arnottianum has been confused with closely related entities for a long time. However, in recent studies (Ali and Khatoon 1982;Shah et al. 2018), those entities are regarded as separate species, namely V. lenifolium (this paper), V. luridum, V. sakesarense and V. stocksii. The inter-species relationships within the V. arnottianum complex (except V. lenifolium) were discussed in Shah et al. (2018). However, there are two associated problems that still need more clarification. Firstly, the type specimen of V. arnottianum was collected from western Himalaya, but the drawings on the herbarium sheet depict characters of a Balochistani species V. luridum, that we recently introduced as a new species in Shah et al. (2018). We hereby present our detailed observations to clarify this first problem.
Robert Wight provided two descriptions of V. arnottianum, notably in the protologue (Wight 1834), and a revised description (Wight 1850). In the former, he described V. arnottianum as a glabrous plant with oblong, obtuse or emarginate leaves, sessile umbels, 5-fid internally hairy corolla lobes, 5-fid corona lobes (shape not provided) equal to the gynostegium. The type designated was "In itinere ad Cashmere, Royle (K [K000872738])". The locality mentioned means "on the way to Kashmir". Kashmir (India) is part of the western Himalaya. For the revised description, Wight acquired specimens from Dr. Stocks collected from Balochistan and named them V. luridum. The name "Vincetoxicum luridum" was limited to those specimens and Stocks did not publish the species. Three specimens of that collection are housed in K, with K001235295 chosen as holotype of V. luridum (Shah et al. 2018). Wight (1850) regarded both K000872738 and Stocks' collections as one species as opposed to Stocks' view. Therefore, in the revised description, Wight (1850) added the following characters: suffruticose, climbing, branches terete, leaves succulent, umbels subsessile, manyflowered, stigma apiculate. In the geographic distribution, he mentions "Beluchistan" (correct spelling is Balochistan or Baluchistan). According to our observations, these revised characters predominantly belong to the Balochistani collections. Therefore, Wight's (1850) revised description is based on two different taxonomic entities. Balochistan is located in south-western Pakistan, not in the Himalayas, and has its own mountain ranges far away from Kashmir (see distribution map in Shah et al. (2018). Wight (1850, p. 17) acknowledged Dr. Stocks for his collections and stated: "This species was first taken up from rather imperfect specimens, whence some alterations have here been found necessary to adapt the character to the species. I am indebted to Dr. Stocks for the specimens from which the drawing and revised character were taken". On the other hand, one of the Stocks' specimens (K001235295) has a manuscript note in Stocks' handwriting "figured by Wight in his Icones from my specimens as his Vincetoxicum arnottianum I doubt". Wight used the term "climbing" in the revised description because he observed Stocks' specimens. He did not use this term in the 1834 description. The illustration provided in 1850 depicts a somewhat climbing habit. The type of V. arnottianum K000872738 does not show a climbing habit. The term "suffruticose" and other characters of the revised description, and some floral and pollinarium drawings were provided on a label of the type specimen K000872738. These observations further indicate that the revised characters as well as the drawings including the pollinarium pertain to Stocks' specimens (Balochistan). The illustration provided in Wight (1850) was also drawn from Stocks' specimens and perfectly resembles the Balochistani collections, not the western Himalayan specimens. During this study, we thoroughly examined the type specimen of V. arnottianum, K000872738, the types of V. luridum ( from western Himalaya and Balochistan. The type of V. arnottianum resembled western Himalayan specimens in its characters and differed from those of Balochistan. Furthermore, the specimens of western Himalaya do not match those of Balochistan in morphological characters and the two areas are geographically distant and climatically different. These findings led us to our decision in Shah et al. (2018) to introduce V. luridum as a new species and maintain K000872738 as the type of V. arnottianum. Our detailed morphological comparison is provided hereby. 1. The type K000872738 is glabrous, which is a character of V. arnottianum (western Himalayan) as also mentioned in the protologue by Wight (1834). Vincetoxicum luridum is densely hairy.
2. In K000872738, the inner surfaces of the corolla lobes are bearded, not pilose like in V. luridum.
3. In K000872738, the inflorescences are not many-flowered like those of V. luridum. 4. In K000872738, the corolla is dark purple as mentioned in the protologue by Wight (1834). In V. luridum, the corolla lobes are bicolored (lower half purple + upper half green). In this taxon, as well as in V. stocksii, flower color can only be correctly determined in fresh flowers.
5. In K000872738, the corolla lobes do not seem twisted because the flowers are immature and pressed. However, we have observed twisted corolla lobes in V. arnottianum while studying fresh flowers. In K000872738, the apex of the flowering bud is acute rather than obtuse as in V. luridum. A twisted corolla is never found in the Balochistani specimens belonging to V. luridum. Secondly, we have observed significant morphological variation in certain populations of V. arnottianum. In these populations, plants are comparatively short (ca. 1 feet or rarely up to 2 feet), leaves are either pubescent ( Fig. 2A-D) or glabrous on both sides ( Fig. 2E-H), flower colour either purple or rarely whitish green, corolla length varies from 2 to 5 mm, corona shape is either rhomboid or deltoid-rhomboid or rarely deltoid. The geography of these populations is different from the typical V. arnottianum. They occur in Rawalpindi district (Punjab province, Pakistan) and in Malakand division (Khyber Pakhtunkhwa province, Pakistan) comprising districts Buner, Chitral, Upper Dir, Lower Dir, Malakand, Shangla and Swat. Geographically, Malakand Division represents the eastern Hindukush mountain range and borders Afghanistan in the west. The major geographic disjunction between Malakand division and the range of typical V. arnottianum (India: Himachal Pradesh, Kashmir; and Pakistan: Azad Jammu, Kashmir, and Hazara Division) is the River Indus. Therefore, in this study, we just highlight this problem and propose to identify the plants possessing the above-mentioned variations as Vincetoxicum sp. aff. arnottianum. We also recommend further detailed studies preferably including a molecular analysis using variable markers to determine whether these populations could potentially prove one or more new taxa in the purple-flowered Vincetoxicum species complex. We cite representative specimens of these populations below.
Distribution and habitat. Endemic to northern Afghanistan. The data on herbarium labels suggest that V. cabulicum grows in clumps on dry slopes of mountains. The elevation range is 1500 to 2800 m.
Phenology. Flowering from May to June and fruiting from June to October. Provisional conservation status. Vulnerable (Table 1). Vincetoxicum cabulicum is collected from a few locations in Afghanistan and appears to be clumped in distribution. There are no reports on grazing. However, a possible threat appears to be habitat destruction through anthropogenic activities.
Distribution and habitat. Two collections of this species are from Shalozan, Kurram valley, Pakistan. This place is located on the eastern border of Afghanistan. The type specimen is collected from Khost, Afghanistan, which is located nearby Kurram Valley. The habitat of the plant is open mountain slopes consisting of small stones and gravel. Elevation ranges from 2100 to 2200 m.
Phenology. Vincetoxicum cardiostephanum flowers from July to August and fruits from August to October.
Provisional conservation status. Critically endangered (Table 1). Vincetoxicum cardiostephanum is extremely rare and comprises very small populations of fewer than 50 individuals. It is known only from three localities in Pakistan and Afghanistan. It was declared critically endangered by Hussain et al. (2019). Erosion is the biggest threat for this species. We have successfully potted a plant in NARC, Islamabad. This indicates that the plant could be conserved in ex-situ conditions.
Notes. In the herbarium (RAW), only one gathering of this species from Kurram Valley, Pakistan was available, collected by Harsukh in 1894 and filed under Cynanchum vincetoxicum (syn. V. hirundinaria). We re-discovered the species from the same area after 122 years. The population was composed of a mere 15 individuals. The type gathering of this species was collected from the adjacent area in Afghanistan.   Undershrubs, up to 40 cm tall. Stem striate, pubescent all around, internodes 1-6.8 cm long. Leaves petiolate; petioles 3-11 mm long, pubescent all around; lamina different shaped: narrowly ovate, oblong-ovate, elliptic ovate, lanceolate-ovate, 4-9.2 × 1.3-3.8 cm; margins smooth; apex acute to obtuse or sometimes mucronulate; base round or cuneate; veins visible on both surfaces, secondary veins 8-12 on each side of midvein; adaxial surface sub-glabrous, adaxial veins densely pubescent; abaxial surface glabrous to sub-glabrous, abaxial veins especially midrib pubescent; margins pubescent. Inflorescences sessile; bracts linear, ciliate; sepals tapering to acute apices, 1.5 mm long with ciliate margins; pedicels 1-3 mm long, pubescent; calycine colleters 5, exceeding the corolla tube in length; corolla green, not twisted, corolla tube 1 mm long, lobes tapering to pointed apex, 2 × 1 mm, bearded within; corona lobes longer than broad, 1 × 0.8 mm, exceeding the length of the gynostegium, base narrow, apex broad, toothed, divergent; staminal appendages obtuse; pollinaria deeply embedded in the gynostegium. Follicles and seeds not seen.

Distribution and habitat. Endemic to eastern Himalayas including India and Nepal and occurring at an elevation of over 2000 m. Herbarium label on W. Dudgeon & L.A. Kenoyer 56 (MO) indicates its habitat to be open grassy places.
Phenology. Flowering from May to June and fruiting from July to October. Provisional conservation status. Data Deficient (Table 1). Vincetoxicum glaucum is collected from a few localities in the eastern Himalayas (India and Nepal). We did not collect or observe its populations in natural habitats. Herbarium labels do not provide significant information about its populations. Therefore, it is declared as data deficient.
Notes. Vincetoxicum glaucum was first described as Cynanchum glaucum Wight but soon regarded as V. canescens by Decaisne (1844), a treatment which Boissier (1879) also adopted. Hooker (1883) reinstated the original name C. glaucum. Rechinger (1970) recognized V. glaucum in a broader sense and lumped with it another Afghani species, V. cabulicum Bornm. Hara et al. (1982) Pakistan, Kashmir and Tibet), whereas V. canescens, a species long regarded as a member of this complex, is endemic to the eastern Mediterranean region and does not occur in southern Asia (also see notes below V. subcanescens). Wight (1834) cited Wallich's collection Asclep. # 133 (Cat. # 8229A) as C. glaucum (corresponding to the typical variety latifolium, denoted by "α" in the protologue), Asclep. # 132 as variety oblongifolium (denoted by "β" in the protologue), and Asclep. # 134 and Cat. # 1554 as variety lanceolatum (denoted by "γ" in the protologue). He did not designate a holotype for C. glaucum, hence the specimens cited in the protologue and their duplicates were the syntypes for the respective varieties. Later on, Hara (1982)  Undershrubs, up to 1 m tall. Stem pubescent all around or along 2 dense lines, internodes 2-13 cm long. Leaves opposite; petioles 1-10 (-14) mm long, equally pubescent all around or sometimes denser along adaxial channel, lamina strongly discolorous, narrow to broadly ovate, 4-10 × 1.8-6.5 cm; apex narrowly acute to very shortly acuminate; base round to sub-cordate to sub-truncate; venation including tertiary and quaternary veins prominent, more prominent and raised on abaxial surface, secondary veins up to 14 on each side of midvein, trichomes absent on both surfaces, sometimes sparsely present on tertiary and quaternary veins, midrib and secondary veins densely pubescent on both surfaces, margins pubescent. Inflorescences mostly sessile, rarely both sessile and short-pedunculate inflorescences present on the same plant, peduncles up to 1.5 cm; bracts linear, up to 2 mm long, pubescent; pedicels 2-8 (-10) mm long, pubescent all around, sometimes pubescent along one or two longitudinal lines. Flowers yellowish-green to green, 4-5 × 2-2.5 mm; sepals tapering to acute or narrowly acute apices, up to 2 mm long, margins sparsely ciliate, calycine colleters 5 or 10 per flower; corolla tube ca. 1 mm long, lobes oblong with obtuse apices, 3-3.5 × 1-2 mm, glabrous within or sparse caducous trichomes present; corona lobes long-triangular with acute apex, slightly divergent, ca. 1 × 0.8 mm, exceeding slightly the length of the gynostegium. Follicles fusiform, up to 7 × 1 cm, apex long-acuminate, surface glabrous, slightly striate. Seeds brown, 6-7 × 3-3.5 mm, wings less than 1 mm broad; coma 2-3 mm long.
Distribution and habitat. Endemic to a long geographic range in the Hindukush Himalayas from Bhutan in the east to Pakistan in the west. The western limit of this species is district Swat (Khyber Pakhtunkhwa province), Pakistan. It occurs on higher elevations between 1500 and 3000 m. The habitats of the species are commonly the Himalayan moist temperate forests (evergreen forests of conifers between 1500 to 3000 m elevations), rarely subalpine or open alpine lands (above 3000 m). We collected it from open stony alpine slopes and stream side slopes in a V-shaped mountain valley. The associated vegetation was either alpine herbs or conifers, and herbaceous to shrubby flora.
Phenology. Flowering from May to August and fruiting from August to October. Provisional conservation status. Least concern (Table 1). Although having highly clumped, distant populations, Vincetoxicum kenouriense spans a wide range in the  Hindukush Himalayas. It is confined to higher altitudes and faces almost no natural threats. Anthropogenic activities, however, are deemed as a potential threat. For instance, two of its populations in Pakistan (in district Bagh, AJK, and district Swat, Pakistan) were found in recreational areas that are expected to undergo changes in the near future which might result in destruction of its habitats. It was also collected previously from Changla Gali (district Abbotabad, Pakistan). In spite of several visits in the past decade, we could not find it anymore in that area. These observations suggest that recreational activities might prove a potential threat to its existence, at least in Pakistan.
Distribution and habitat. Endemic to Khyber Pakhtunkhwa province of Pakistan. So far, it has been recorded from North & South Waziristan and Kohat districts. The elevation ranges from 1500 to 2000 m. Its habitat is open rocky slopes consisting of small stones and gravel and stream beds.
Etymology. The name is based on smooth, mostly glabrous, leaves of the species. Phenology. Flowering from April to June and fruiting from July to August. Provisional conservation status. Endangered (Table 1). Vincetoxicum lenifolium is endemic to a small range comprising three districts of Khyber Pakhtunkhwa province, Pakistan. In 2016, we collected fresh specimens and observed its population structure in Razmak (North Waziristan). The population was clumped with less than 20 individuals. Anthropogenic activities like land degradation, settlements, roads etc. are deemed major threats to its existence.
Notes. From the general appearance, V. lenifolium appears as a closely related member of the purple-flowered Vincetoxicum including V. arnottianum, V. luridum, V. sakesarense and V. stocksii. The paratypic specimens of this species were hitherto misidentified as V. arnottianum or V. hirundinaria. However, the new species is easily distinguished by ovate leaves, green flowers and glabrous corolla from V. arnottianum and by inconspicuous veins, denser inflorescences and small rhomboid corona from V. hirundinaria. RAW houses a variable specimen, N. Ali 1029, which is silvery in appearance, with sessile inflorescences and corona lobes somewhat deltoid (Fig. 3H).
These characters and the associated geographic information do not support the recognition of the specimen as a separate taxon. The specimen is cited as V. lenifolium in this treatment. Long-pedunculate inflorescences are most commonly found in V. lenifolium and rarely in V. stocksii. Short-pedunculate along with sessile inflorescences are found in V. arnottianum, V. cabulicum, V. cardiostephanum, rarely in V. kenouriense and V. sakesarense, V. luridum, V. stocksii, and V. subcanescens petioles up to 8 mm long, pubescent along adaxial channel, sometimes sparsely pubescent abaxially; lamina narrowly ovate to lanceolate, 3-11 × 1-3 cm; apex acute to narrowly acute; base round to sub-cuneate, veins visible on both sides, secondary veins 6-7 (-12) on each side of midvein, both adaxial and abaxial surfaces and abaxial veins glabrous, adaxial veins pubescent, margins sparsely pubescent. Inflorescences sessile, rarely small peduncles up to 2 mm present; bracts with a few basal trichomes or completely glabrous. Flowers dark purple except sepals, 4 × 2.5 mm; pedicels 2-5 mm long, puberulent; sepals up to 2 mm long, tapering into narrowly acute to acuminate apices, margins ciliate, abaxial surface sometimes pubescent, calycine colleters 10/flower; corolla tube up to 1 mm long, lobes 2.5 × 1 mm, twisted clockwise, gradually tapering to the apex, inner surface of corolla lobes bearded except one lateral margin; corona lobes deltoid, longer than wide, 0.6 × 0.5 mm, almost reaching the bases of the staminal appendages, divergent. Follicles fusiform, 5.5-6.5 × 0.7 cm, apices acuminate, surface inconspicuously striate, glabrous. Seeds not seen.
Distribution and habitat. Endemic to a protected area in Soon Sakesar Valley, a small mountainous valley in northern Punjab, Pakistan. The maximum elevation is 1500 m.
Phenology. Flowering from April to September and fruiting from May to October. Provisional conservation status (Table 1). Critically endangered. Vincetoxicum sakesarense is known from two localities in Soon Sakesar valley, Salt Range, Punjab province, Pakistan. The area is protected for security purposes. We and other botanists have collected the species from the type locality twice in the current decade. The species is critically endangered due to the fact that its EOO is very small ( Table 1), and that it is confined to a comparatively small mountain range. Expanding human population coupled with anthropogenic activities are a serious threat. We have grown living plants in NARC, Islamabad. This indicates that this species could potentially be conserved outside its native range.
Distribution and habitat. Endemic to eastern Himalayan Mountains of India. The elevation range is 6000 to 7000 m. The limited herbarium materials do not provide more information.
Phenology. Vincetoxicum stewartianum flowers and fruits from August to September. Provisional conservation status. Data deficient (Table 1). Vincetoxicum stewartianum is gathered from only the type locality. Besides label data on gatherings from the type locality, information is lacking about its present occurrence. A survey on its occurrence and ecology is recommended.
Distribution and habitat. Endemic to Zhob and Qila Saifullah districts in northeast Balochistan, Pakistan. It is found on dry stream beds made up of soil, stones and gravel. Its elevation ranges from 1300 to 2100 m.
Phenology. Vincetoxicum stocksii flowers from April to June and fruits from June to August. (Table 1). Vincetoxicum stocksii is endemic to two districts in Balochistan province, Pakistan. The populations are partially fragmented and face the threat of habitat loss especially on the dry stream beds due to rains.

Provisional conservation status. Vulnerable
Notes. Vincetoxicum stocksii is a member of the purple-flowered group. Before its description as a new species by Ali and Khatoon (1982), it was identified as V. arnottianum. Recently, Shah et al. (2018) disintegrated V. stocksii into two species, separating from it V. luridum, an endemic of southwest Balochistan based on indumentum type on vegetative parts, corona lobes shape, pollinarium morphology and seed coat ornamentation. Vincetoxicum stocksii can be easily differentiated from V. arnottianum by the smaller pubescent leaves, the non-twisted and internally pilose corolla lobes, and the subulate corona lobes. These characters also differentiate it from V. sakesarense. The presence of both sessile and distinctly pedunculate inflorescences on the same plant is a common character shared between V. stocksii and V. lenifolium. However, green flowers, glabrous corolla lobes and smaller rhomboid corona lobes readily distinguish V. lenifolium from V. stocksii.  Undershrubs, up to 75 cm tall. Stem and other vegetative parts sub-canescent, internodes 1-9 cm long, striate. Leaves opposite, rarely whorled on some nodes; petioles 1-18 mm long; lamina discolorous, narrow to broadly ovate to sometimes lanceolate-ovate, 3-9 × 1.2-4.8 cm; apex acute to narrowly acute to shortly acuminate; base rounded to sub-cordate to sub-truncate; veins visible on both sides, more prominent on adaxial side, secondary veins 6-12 on each side of midvein, tertiary veins sometimes visible, lamina sub-canescent on both sides. Inflorescences sessile or both sessile and pedunculate inflorescences present on the same plant; peduncles up to 2.5 cm long, sub-canescent; bracts narrow with a few marginal trichomes; pedicels 2-7 mm long, pubescent. Flowers green to yellowish-green, 3-4 × 2-2.5 mm; sepals tapering into acute to narrowly acute apices, pubescent along margins and abaxial surface, up to 2 mm long, calycine colleters single or in pairs; corolla tube ca. 1 mm long, lobes tapering into obtuse apex, 2-2.5 × 1-1.5 mm, margins appearing wavy in dry flowers, sub-bearded within; corona lobes clavate, 0.5-1 × 0.2-0.5 mm, reaching the base, the middle or, rarely, the apex of the staminal appendages, divergent. Follicles fusiform, 4.5-9.5 × 0.7-1 cm, sparsely pubescent, minutely striate, apex narrowly acuminate. Seeds 5-6 × 2-3 mm, wings up to 1 mm broad; coma up to 3 mm long.
Distribution and habitat. Endemic to Pakistan (Chitral, Dir, Swat and Gilgit Baltistan), Kashmir (Ladakh) and China (Tibet). The habitat of the species is open slopes. Soil type is clay to gravel to large size stones. The elevation ranges from 1600 to 2800 m.
Etymology. The name is based on the sub-canescent indumentum on the vegetative parts of the plant.
Phenology. Vincetoxicum subcanescens flowers from April to August and fruits from May to October.
Provisional conservation status. Least concern (Table 1). Vincetoxicum subcanescens is common in its range. However, the populations are extremely distant and clumped. Vernacular name. Lovaki (in Chitrali language). Notes. Vincetoxicum subcanescens was previously misidentified as V. canescens (Ali and Khatoon 1982;Boissier 1879). Rechinger (1970) treated it as V. glaucum in Flora Iranica and also synonymized V. cabulicum with it. Vincetoxicum subcanescens differs from V. canescens by the subcanescent indumentum, smaller flowers, clavate corona lobes, and glabrous and narrowly fusiform follicles. Vincetoxicum canescens is distributed in the eastern Mediterranean region in Turkey, Greece, Syria and Iraq. It is characterized by canescent indumentum, larger flowers, arrow-shaped corona lobes, and ovate and canescent follicles. Vincetoxicum glaucum exhibits variable leaf shapes, sub-glabrous or glabrous leaf surfaces, sessile inflorescences and toothed corona lobes. It is distributed in the Himalayas of India and Nepal. The closest relative of V. subcanescens is V. cabulicum which differs by the sub-sessile leaves and dark purple corolla and is endemic to northern Afghanistan.