Vincetoxicum siamicum sp. nov. (Asclepiadeae, Asclepiadoideae, Apocynaceae), a rheophyte from Northeastern Thailand and preliminary observation on its in situ pollen germination

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Vincetoxicum siamicum A.Kidyoo, newly described here, is a rheophytic herb growing in dense clumps near or in streams in northeastern Thailand. Here I provide a diagnosis and detailed description of this new species, as well as illustrations and photographs. Several characters of V. siamicum are compared with those of V. stauntonii, considered to be a close relative. These two species display consistent differences in leaf arrangement and corona structure. A comparison with other rheophytic species, V. glaucescens, V. hydrophilum, V. riparium, V. verticillatum, is also provided. They differ in several traits: shape, size and texture of leaves, hairiness of corolla lobes, branching pattern of inflorescences and elevations at which they occur. In addition, in situ pollen germination observed in the flowers of V. siamicum is reported.

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... Lately, based on morphological and chemical data, Liede (1996) recognized Vincetoxicum as a separate genus from Cynanchum and treated Tylophora Brown (1810:460) as the closest relative of Vincetoxicum. Vincetoxicum usually has colourless latex, fascicled roots, patent to horizontal corolla lobes, and a fleshy staminal corona, while Tylophora is characterized by twining or rarely erect habit, small flowers with rotate or subrotate and deeply 5-lobed corollas, a corona of five erect, turgid lobes, and small globose to subglobose pollinia in horizontal to erect position (Forster 1991, 1992, Kidyoo 2016. ...
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Vincetoxicum xinpingense, a new species from the Ailao Mountains in Yunnan Province, China, is described and illustrated. It is morphologically similar to V. sublanceolatum, Tylophora forrestii, and T. chingtungensis, but can be distinguished by several characters: shape and size of leaves, size of corolla lobes, length and shape of corona, attachment position of corona to the anthers, and orientation of pollinia. In addition, conservation status and other relevant notes are provided.
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An unknown Vincetoxicum species has recently been discovered in northeastern Thailand. It is a twiner that resembles in its morphology and ecology V. flexuosum var. flexuosum , a variable species widely occurring from tropical Asia to Australia. Comprehensive morphological examination showed that despite similarities in growth habit, leaf shape, branching of the inflorescence and flower colour, these two taxa exhibit substantial differences in both vegetative and reproductive traits that clearly distinguish one from the other, particularly shape of the flower bud and indumentum on the corolla lobes. In addition, we also evaluated phylogenetic relationships based on DNA sequence data for ITS, trn T-L, trn L, and trn L-F markers of this new Vincetoxicum sp. with congeners (including, inter alia, new sequences of V. flexuosum var. flexuosum and also those of V. flexuosum var. tenuis , the other variety occurring in Thailand). The analyses demonstrated that the new Vincetoxicum sp. is not closely related to the taxa recognized as V. flexuosum. The new species was instead retrieved as sister to a clade containing the African taxa, V. caffrum , V. lycioides and V. fleckii . Therefore, integrated analyses of morphology and molecular phylogeny revealed Vincetoxicum sp. to be a well-defined species clearly distinct from V. flexuosum , as well as from all other known congeners. The morphological similarity between the new Vincetoxicum sp. and V. flexuosum var. flexuosum likely resulted from convergence, leading to various taxonomic complications. We here describe it as a new species, V. sangyojarniae , sp. nov., and provide a detailed description, illustration, photographs, and comparison to the morphologically similar V. flexuosum var. flexuosum . A preliminary taxonomic reconsideration of the infraspecific taxa under V. flexuosum is also suggested.
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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. lenifolium sp. nov. (endemic to Pakistan), V. stewartianum sp. nov. (endemic to India), and V. subcanescens sp. 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.
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Hoya phuluangensis Kidyoo, a new species from northeastern Thailand is here described and compared to the similar species, H. rostellata and H. siamica. All three species have glabrous stems and branches, glabrous coriaceous leaves, adaxially puberulent ovate corolla lobes with an acute apex, and flat to slightly erect coronal scales with an obtuse or rounded apex. However, H. phuluangensis differs from the other two species in the following characters: flowers with a shallow cup-shaped corolla tube and a corona diameter measuring less than half of the corolla tube diameter. Full description of H. phuluangensis is provided, together with line drawings and photographs. In addition, three new combinations and two new names in the genus Vincetoxicum, namely V. indicum (Burm.f.) Mabb. var. glabrum (Decne.) A. Kidyoo, V. kerrii (Craib) A. Kidyoo, V. sootepense (Craib) A. Kidyoo, V. lindleyi A. Kidyoo and V. potamophilum A. Kidyoo, are proposed.
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identification keys to the taxa of Asclepiadaceae recorded from China with their descriptions and distributions.
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A revised phylogeny of Tylophorinae, based on 77 species of all genera presently attributed to the subtribe (Biondia, Blyttia, Diplostigma, Goydera, Pentatropis, Pleurostelma, Rhyncharrhena, Tylophora, Vincetoxicum) is presented. Five chloroplast markers (trnT-L, trnL-F, and psbA-trnH intergenic spacers as well as the trnL and trnG introns) and two nuclear markers (ITS, ETS) were used, totalling in 3809 base pairs. Tylophorinae are strongly monophyletic and consist of several well-defined clades. Backbone resolution between these clades is low, indicating a rapid early radiation. Pentatropis is sister to all remaining taxa, albeit with weak support; all other taxa form one big clade not corresponding to previous generic delimitations. Therefore, all genera except for Pentatropis are subsumed under Vincetoxicum. The early branching clades of Vincetoxicum s.l. all grow in Africa, where the group originated ca. 18 Ma ago, correlating with the closure of the Tethys Ocean. The first round of differentiation took place between 12 and 15 Ma ago, resulting in Tylophorinae being distributed over almost all of their present range except for South Africa, Arabia and Europe. Two unrelated lineages of temperate, mostly erect plants hitherto named “Vincetoxicum” have arisen from more tropical lineages, hitherto named “Tylophora ”. One clade of African species is nested inside the Australasian assemblage; this clade contains exclusively polyploid species and its re-immigration to Africa took place in the Messinian, at ca. 6.8 Ma. The European Vincetoxicum species split from erect steppe plants of temperate Asia at ca. 4.5 Ma, coinciding with the uplift of the Tibetan plateau. This group contains two species that are presently aggressively spreading in North America after chance introductions.
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The complex floral morphologies found in the Asclepiadoideae (Apocynaceae sensu Endress & Bruyns 2000) have intrigued and perplexed botanists for two centuries. Recent work has given us a good idea of broad-based concepts of structure, anatomy, and homology (e.g.. However, little of this work has been placed in a functional context, except as laboratory-based hypotheses as to the function of specific tissues and organs (though see Kunze 1998, 1999). Valuable though such speculations are, they require confirmation from field data. On the other hand, pollination ecologists have usually dealt with taxa whose morphologies are comparatively well known and which exist as large populations in developed countries (e.g., the well studied genus Asclepias; see review by Wyatt & Broyles 1994), or have recorded limited data on the links between form and function (though see Vogel 1961, Kunze 1991). For the vast majority of the " asclepiads " we have no idea of the exact role (if any) in pollination of particular combinations of flower morphology, color, patterning, scent, etc. A characteristic floral structure of the Asclepiadoideae is the possession of a corona of staminal or corolline origin (for typology, see Liede & Kunze 1993). In Asclepias, and some other genera, the corona lobes function as nectar receptacles which effectively serve to position an insect into the appropriate orientation for removal and/or insertion of pollinia. In other genera the function of the corona is not so clear, though it may act to mechanically guide an in-sect's body parts to the guide rails. In some taxa with reduced or absent coronas (for example Microloma, Astephanus) this function is transferred to the corolla or trichomes originating on the inner corolla surface. Observations of pollinator behavior in relation to corona morphology are urgently required in order to gain a fuller understanding of corona function. Cynanchum is a large genus of some 400 described species with a tropical and subtropical distribution in Africa, Madagascar, Australia, North and South America, and parts of Asia (Liede 1997). It is characterized by a staminal corona originating from a ring-shaped meristem (Kunze 1991) that can be extremely variable in shape and relationship to the gynostegium, especially in Madagascar, which is a center of diversity for the genus. Pollination observations in Cynanchum are scarce; only eight species have ever been observed for pollinators (Ollerton & Liede 1997; see ASCLEPOL, our on-line database of pollinators of the " Asclepiadaceae " , at: departments/planta2/research/floral.htm). During fieldwork in Gabon in 1997, the opportunity arose for one of us (JO) to observe pollinators visiting Cynanchum adalinae subsp. adalinae (K. Schum.) K. Schum. and to make observations on the relationship between corona structure and function in this tropical African taxon. In addition, the second author (SL) has collected data on variation in fruit SHORT COMMUNICATIONS
The genera Cynanchum and Vincetoxicum are revised for the Flora Malesiana area. For Cynanchum, nine species are recognized and one new subspecies is described. For Vincetoxicum, only one species, the widespread V. carnosum, occurs in the area. Five published species of Cynanchum have to remain obscure, because the types most likely got destroyed in Berlin.
Vincetoxicum sensu lato is a tropical lineage comprising two clades that have reached high northern latitudes. Of the temperate clades, one is restricted to the Far East, the other one (Vincetoxicum s. str. Clade) extends into Europe, but their ranges overlap in Central China and Japan. Three species invasive in North America, V. hirundinaria, V. nigrum and V. rossicum, are members of the Vincetoxicum s. str. Clade. We explore the prerequisites for the range expansion in the Vincetoxicum s. str. Clade performing Bayesian and Maximum Likelihood phylogenetic analyses on sequences of the nuclear internal transcribed spacer (ITS) region, the nuclear external transcribed spacer region (ETS), and five plastid markers. The resulting phylogeny is used to conduct biogeographic analysis using BioGeoBEARS to reconstruct ancestral species ranges. Moreover, we map the known occurrences of two rare characters in Asclepiadoideae, the possession of phenanthroindolizidine alkaloids and reported cases of autogamy onto our phylogeny. Finally, we have conducted ecological niche modelling using Maxent on a total of 220 spatially unique occurrences of nine Vincetoxicum s. str. species spanning more than 4000 km along the east–west gradient to learn about the climatic conditions along the presumed migration route. Our results indicate a north-westward migration in Vincetoxicum s. str. along the Asian mountain chains to Europe. Climatic preferences of the nine species sampled are dissimilar, except for the common exposure to at least one month of subfreezing temperatures, indicating a rather wide climatic tolerance for the clade as a whole. The three species invasive in North America belong to the northern Eurasian subclade and show the rare combination of phenanthroindolizidine alkaloids and autogamy.
Monophyly and sister group relationship of Ceropegieae and Marsdenieae, the two Asclepiadoideae tribes possessing erect pollinia, are confirmed by molecular investigation of non-coding cpDNA markers (trnT-L and trnL-F spacers, and the trnL intron). In Ceropegieae, the analyzed taxa fall in four subclades. The Heterostemma subclade is sister to other three subclades, of which the Conomitra-Leptadenia-Orthanthera subclade is sister to the Anisotoma-Neoschumannia-Riocreuxia-Sisyranthus subclade and to the large subclade comprising the stem-succulent stapeliads, Brachystelma and Ceropegia. Following these results, subdivision of Ceropegieae into four subtribes, Anisotominae, Heterostemminae, Leptadeniinae and Stapeliinae, is proposed.
On the basis of morphological and chemical data, the genus Vincetoxicum is recognized as separate from Cynanchum. Tylophora is identified as the closest relative of Vincetoxicum. In consequence, eleven new combinations in Vincetoxicum are proposed. The C. auriculatum group is recognized as C. sect. Rhodostegiella. Tylophoropsis must be included in Tylophora, which results in one new combination.
This paper is a precursor to the account of the Asclepiadaceae in the Flora of China. A new genus and species, Sichuania alterniloba, is described. Twenty-four new species are described in Biondia (B. crassipes, B. laxa, B. parviurnula, B. revoluta, and B. tsiukowensis), Ceropegia (C. sinoerecta), Cynanchum (C. bicampanulatum, C. brevicoronatum, C. duclouxii, C. kingdonwardii, C. longipedunculatum, C. megalanthum, C. pingshanicum, C. rockii, and C. sinoracemosum), Hoya (H. commutata and H. mekongensis), Marsdenia (M. brachyloba, M. tenii, and M. yuei), and Tylophora (T. forrestii, T. rockii, T. tuberculata, and T. uncinata). Jasminanthes is resurrected. Eleven new combinations are proposed in Ceropegia (C. exigua), Cynanchum (C. boudieri subsp. caudatum), Heterostemma (H. menghaiense), Hoya (H. chinghungensis), Jasminanthes (J. chunii, J. mucronata, J. pilosa, and J. saxatilis), and Tylophora (T. costantiniana, T. oligophylla, and T. tsiangii). The new name Cynanchum triangulare is proposed to replace C. deltoideum Hooker, not Hance. New synonymy is proposed in Cynanchum, Lygisma, Marsdenia, and Tylophora. The status of Merrillanthus is discussed.
The phylogenetic structure of Asclepiadoideae (Apocynaceae) has been elucidated at the tribal and subtribal levels in the last two decades. However, to date, the systematic positions of seven Asian genera, Cosmostigma, Graphistemma, Holostemma, Pentasachme, Raphistemma, Seshagiria and Treutlera, have not been investigated. In this study, we examine the evolutionary relationships among these seven small enigmatic Asian genera and clarify their positions in Asclepiadoideae, using a combination of plastid sequences of rbcL, rps16, trnL and trnL- F regions. Cosmostigma and Treutlera are resolved as members of the non-Hoya clade of Marsdenieae with strong support (maximum parsimony bootstrap support value BSMP=96, maximum likelihood bootstrap support value BSML=98, Bayesian-inferred posterior probability PP=1.0). Pentasachme is resolved as sister of Stapeliinae to Ceropegieae with moderate support (BSMP=64, BSML=66, PP=0.94). Graphistemma, Holostemma, Raphistemma and Seshagiria are all nested in the Asclepiadeae-Cynanchinae clade (BSMP=97, BSML=100, PP=1.0). The study confirms the generally accepted tribal and subtribal structure of the subfamily. One exception is Eustegia minuta, which is placed here as sister to all Asclepiadeae (BSMP=58, BSML=76, PP=0.99) and not as sister to the Marsdenieae+Ceropegieae clade. The weak support and conflicting position indicate the need for a placement of Eustegia as an independent tribe. In Asclepiadeae, a sister group position of Cynanchinae to the Asclepiadinae+Tylophorinae clade is favoured (BSMP=84, BSML=88, PP=1.0), whereas Schizostephanus is retrieved as unresolved. Oxystelma appears as an early-branching member of Asclepiadinae with weak support (BSMP=52, BSML=74, PP=0.69). Calciphila and Solenostemma are also associated with Asclepiadinae with weak support (BSMP=37, BSML=45, PP=0.79), but all alternative positions are essentially without support. The position of Indian Asclepiadoideae in the family phylogeny is discussed.
We investigated the effect of self-pollination on fruit- and seed-set in Asclepias exaltata, a self-incompatible milkweed. A total of 1,380 hand-pollinations were performed on 138 flowers in each of five treatments. In each treatment, two pollinia were placed in adjacent stigmatic chambers, which transmitted pollen tubes to the same ovary. Treatments 1 and 2 involved simultaneous placement of two self-pollinia (treatment 1) or two cross-pollinia (treatment 2) into adjacent stigmatic chambers. No fruits were produced after self-pollinations, but 23% of the cross-pollinated flowers matured fruits. The three remaining experimental pollination treatments were self-pollination preceding cross-pollination by 24 hr (treatment 3), simultaneous self- and cross-pollination (treatment 4), and cross-pollination preceding self-pollination by 24 hr (treatment 5). Compared with that in flowers receiving only cross-pollen, fruit-set in treatments 3-5 was reduced 81%, 49%, and 29%, respectively. Seed-set was also significantly reduced in flowers receiving self-pollen 24 hr in advance of the cross-pollen. Using genetic markers, we observed that only 0.6% of seeds resulted from self-pollination. Our data strongly suggest that self-pollination in milkweeds not only wastes pollen but also greatly reduces the number of ovules and ovaries that might otherwise mature fruits and seeds after cross-pollination.
Asclepiadaceae are the dicot counterparts to the Orchidaceae, which also transmit their pollen grains in large groups within pollinia. Unlike many terrestrial, nectar-producing orchids, however, milkweeds are characterized by low fruit-set, typically averaging 1-5%. Transfer of hundreds of pollen grains as a unit makes it possible to quantify pollinator activity and male and female reproductive success more directly and more easily in milkweeds than in plants with loose pollen grains. It also leads to the production of fruits whose seeds all share a single father, thus simplifying paternity analysis. Recent anatomical work has demonstrated that three of the five stigmatic chambers of milkweed flowers transmit pollen tubes to one of the two separate ovaries, whereas the other two chambers transmit only to the second ovary. Milkweed flowers are long-lived and produce copious nectar, which flows from nectaries within the stigmatic chambers to fill the hoods, which serve as reservoirs. Nectar also serves as the germination fluid for pollen grains, but concentrations above 30% inhibit germination. Most milkweeds are genetically self-incompatible and express an unusual late-acting form of ovarian rejection. Some weedy milkweeds, however, are self-compatible, and levels of self-insertion of pollinia are apparently high in these, as well as in self-incompatible, species. Early attempts to explain the evolution of inflorescence size in milkweeds were hampered by failure to consider the genetic basis of the variation observed and by failure to determine the unit on which selection should act. Direct tests of the ''pollen donation'' hypothesis have cast doubt on the validity of the view that flower number and other floral traits evolved primarily to enhance male reproductive success. Milkweeds are pollinated by a diverse array of large bees, wasps, and butterflies, and these generalist pollinators effect extensive gene flow within and between populations, augmented by wind dispersal of comose seeds. Morphological and biochemical evidence support the view that limited, localized hybridization occurs between sympatric species of milkweeds.
Scanning electron and fluorescence microscopy were used to clarify some aspects of the floral morphology ofApocynum cannabinum. Insects are required for pollination, since the floral morphology prevents autogamy and minimizes intrafloral self-pollination. Flowers hand-pollinated with self-pollen never set fruit, but 10.6% of cross-pollinations produced fruit. Self-pollen did germinate, however, and produced abundant tubes that grew through the pistil and entered the ovule micropyles. The proportion of ovules penetrated by self- and outcross-pollen tubes was not statistically significantly different. These results suggest thatA. cannabium possesses late-acting self-incompatibility, similar to that in the closely related Asclepiadaceae.
Reproductive character and genetic diversity were investigated for an autogamous species of Tylophora matsumurae endemic to the Ryukyu Islands and its progenitor species T. tanakae. Approximately one-fourth of bagged flowers set fruits in T. matsumurae, although no fruits were obtained from bagged flowers in T. tanakae. In situ pollen tube germination was observed with high frequency in all five populations examined in T. matsumurae. Furthermore, in T. matsumurae, anther sacs were not dehisced even at anthesis. These results suggest the highly autogamous nature of T. matsumurae. No allozymic variation was detected in all seven populations examined in T. matsumurae. The phenogram constructed using the neighbor-joining method based on Nei's unbiased genetic distance indicated that T. matsumurae clustered with the Okinoerabu Island population of T. tanakae. The estimated outcrossing rate of four populations of T. tanakae varied from 0.18 to 0.59. It is probable that T. matsumurae had been derived from the predominantly self-pollinating population of T. tanakae, and rapidly enlarged its distribution area.
The phylogeny of the genus Cynanchum s. str. is studied using cpDNA spacers and ITS. Morphological, anatomical and latex triterpenoid data are interpreted in light of the molecular results, and discrepancies are discussed. Vegetative characters are better indicators of relationship than floral characters, especially corona characters. The monophyly of all Malagasy species and, nested within the latter, of all stem-succulent taxa is ascertained and the genera Folotsia, Karimbolea, Platykeleba and Sarcostemma are subsumed under Cynanchum. One African species, C. galgalense, is excluded from Cynanchum.
Comparisons of the causes and consequences of cross- and self-fertilization have dominated research on plant mating since Darwin's seminal work on plant reproduction. Here, I provide examples of these accomplishments, but also illustrate new approaches that emphasize the role of floral design and display in pollen dispersal and fitness gain through male function. Wide variation in outcrossing rate characterizes animal-pollinated plants. In species with large floral displays, part of the selfing component of mixed mating can arise from geitonogamy and be maladaptive because of strong inbreeding depression and pollen discounting. Floral strategies that separate the benefits of floral display from the mating costs associated with geitonogamy can resolve these conflicts by reducing lost mating opportunities through male function. The results from experiments with marker genes and floral manipulations provide evidence for the function of herkogamy and dichogamy in reducing self-pollination and promoting pollen dispersal. Evidence is also presented indicating that increased selfing resulting from changes to floral design, or geitonogamy in large clones, can act as a stimulus for the evolution of dioecy. The scope of future research on mating strategies needs to be broadened to include investigations of functional links among flowers, inflorescences and plant architecture within the framework of life-history evolution.
Molecular phylogenetic analyses of Vincetoxicum and Tylophora (Apocynaceae-Asclepiadoideae) were conducted based on the nucleotide sequences of cpDNA (two intergenic spacers of trnL (UAA)-trnF (GAA) and psbA-trnH and three introns, i.e., atpF, trnG (UCC) and trnL (UAA)), and nrDNA (ITS and ETS regions). Our phylogenetic analysis revealed two monophyletic groups; one consisted of seven taxa of Tylophora and Vincetoxicum inamoenum, Vincetoxicum magnificum and Vincetoxicum macrophyllum (Clade I) and the other consisted of 17 accessions of Vincetoxicum (Clade II). The monophyly of the genus Vincetoxicum was not supported. Although many nucleotide substitutions were observed in Clade I, the genetic differentiation within Clade II was small. Low genetic diversification but considerable morphological divergence suggests that the species in Clade II had undergone rapid diversification. Although most species in Clade I have tiny flowers, those in Clade II have larger and more nectariferous ones. Thus, we hypothesized that the rapid morphological radiation in Clade II may have been due to the gaining of floral characters such as large flowers and large amounts of nectar corresponding to diverse pollinators.
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