Vincetoxicum nigrum (black swallow-wort)

Identity

Preferred Scientific Name

• Vincetoxicum nigrum (L.) Moench

Preferred Common Name

• black swallow-wort

Other Scientific Names

• Alexitoxicon nigrum (Moench) St.-Lag
• Antitoxicum nigrum (Moench) Pobed.
• Asclepias alexitoxica St.-Lag.
• Asclepias nigra L.
• Asclepias toxicaria Salisb.
• Cynanchum atrum (Jord. & Fourr.) Breistr.
• Cynanchum barbatum L.f. ex Schult.
• Cynanchum fuscum Schult.
• Cynanchum louiseae Kartesz and Ghandhi 1994
• Cynanchum louiseae Kartesz & Gandhi
• Vincetoxicum atrum Jord. & Fourr.

International Common Names

• English: black dog-strangling vine; black swallow-wort; climbing milkweed; climbing poison; dark vincetoxicum; Louis’ swallow-wort
• French: dompte-venin noir

Local Common Names

• Germany: Schwalbenwurz, Schwarzer

EPPO code

• CYKLO (Cynanchum louiseae)

Summary of Invasiveness

V. nigrum is a herbaceous climbing vine native to south-western Europe (Italy, France, Portugal and Spain). It has spread extensively throughout New England, the lower Hudson River basin and south-eastern Pennsylvania, USA. V. nigrum produces a large number of wind-borne, self-fertile seeds which readily disperse to new sites. Small patches of V. nigrum can coalesce to form large, monospecific stands that outcompete with native vegetation and alter habitats. In Vermont and New Hampshire, USA, the endemic and endangered species, Astragalus robbinsii var. jesupii, is under pressure by an expanding population of V. nigrum. In addition to this V. nigrum may have negative impact on the monarch butterfly, Danaus plexippus.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Gentianales
•                         Family: Asclepiadaceae
•                             Genus: Vincetoxicum
•                                 Species: Vincetoxicum nigrum

Notes on Taxonomy and Nomenclature

Other names for the genus Vincetoxicum Wolf (1776) include Vincetoxicum Medik., Alexitoxicum St. Lag., Cynanchum (L.) Pers., Cynanchum (L.) R. Br. and Antitoxicum Pobed. In North America, synonyms for Vincetoxicum nigrum include Cynanchum nigrum and C. louiseae. No consensus exists for the distinction between Vincetoxicum and Cynanchum.

A study by Liede and Täuber (2002) found significant distinctions between Old and New World Cynanchum species, more so than between other established Asclepiadaceae genera. Liede (1996) separated Vincetoxicum from Cynanchum on the basis of the presence of certain alkaloids and glycosides in Vincetoxicum that are lacking in Cynanchum, using these as indicators of phylogenetic distance. Others find the variation of these two genera to be too continuous to separate them (Woodson, 1941; Kartesz, 1999).

Description

V. nigrum is a rhizomatous, perennial herbaceous suberect, climbing and twining vine growing from a fibrous root system with several subterranean buds at the stem base producing one (or more) puberulent stems which annually grow to 1-3 m high. Leaves are opposite, 5-12 cm long, oblong to ovate, acuminate, rounded to subcordate at the base, with short (10-15 mm) petioles.

The 5-lobed dark to very dark purple flowers are in groups of 6-10 in umbelliform cymes in the axils of leaves, peduncles 1-3 cm, pedicels glabrous, flowers 6-8 mm in diameter. Corolla lobes have straight white hairs on the upper surface and are fleshy, deltoid, about as wide as long (1.5-3 mm), segments joined by a connective membrane 2/3 their length, gynostegium pale green. The fruits are slender, smooth follicles, 5-7 cm long by 0.8 cm wide, often in pairs. Seeds comose.

Plant Type

Distribution

V. nigrum is native to western European Mediterranean regions such as France, Italy, Spain and Portugal. V. nigrum has been introduced into North America where it is primarily in south-eastern New York, eastern Massachusetts and southeastern Pennsylvania, USA. Smaller populations are scattered in Ontario and Quebec, Canada and in the mid-western USA and southern California.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

The earliest herbarium record for North America is from 1854 and was collected in Ipswich, Essex County, Massachusetts, USA. The next, collection was 1864 from the same county. This indicates that the plant escaped from a botanic garden. The first herbarium record in New York State was 1874. By the twentieth century it was known from nine states (Sheeley, 1992) and today it is currently in at least 21 states of the USA (USDA-NRCS, 2016).

The first herbarium record in Canada was from Montreal, 1949, near the arboretum of Notre Dame College (Pringle, 1973). Regional flora, such as Gray's Manual of Botany (1868 edition), indicate that the plant escaped from cultivation in gardens.

Risk of Introduction

It is possible that accidental introductions of V. nigrum will continue via agricultural commodities, contaminated soil and vines/seeds caught on equipment. In addition to this, seeds of this species are available online for sale and the attractive flowers and pods invite collection by an uneducated public.

In the USA The state of Vermont, has included V. nigrum in a noxious weed quarantine list. It is included on invasive plant lists for New York State and the New England states, but the lists have no regulatory power.

Habitat

V. nigrum is found in a wide range of upland habitats including woods and moist sunny places (Gleason and Cronquist, 1991). Habitat in its native western Mediterranean region is slopes, copses and stony dry areas from sea-level to 580 m, for instance in the Pyrenees (Fournier, 1977).

In North America, where it has escaped cultivation, V. nigrum habitat is widely varied including sunny, open areas, shrub habitats and fully shaded forest on substrates ranging from rocky slopes and stony dry areas to riparian terraces, stony shores and garden soils, at altitudes from sea level to at least 300 m. Coastal and roadside infestations are common, indicating a probable tolerance of alkaline soils. It is associated with calcareous soils, but may also be found in granite-based soils.

Habitat List

Biology and Ecology

Genetics
The chromosome number of V. nigrum (Cynanchum nigrum Pers.) is 2n=44.

Physiology and Phenology

The polyembryonic seeds of V. nigrum germinate in autumn and spring, with improved germination after vernalization, yielding 1-4 seedlings (Lumer and Yost, 1995). A fibrous root system radiates from the crown. Seedlings have pointed ovate leaves. First-year growth is juvenile. Plants are clonal with a deep rhizome system (Lumer and Yost, 1995). Perennating buds on the root crown readily sprout after top destruction. In successive years, plants emerge in May and expand rapidly. Twining begins as flower buds begin to enlarge. Flowering occurs from mid to late May until mid-July, with diminished flowering during September. Flowers begin to open just after sunrise, remaining open for six to eight days. Fruit dehisce and release seeds from mid-August until early October in New York State, USA (Lumer and Yost, 1995). The seeds bear a coma (a tuft of silky hairs). The plants senesce after seed dispersal. Dead stems persist through winter and the successive growing season.

Reproductive Biology

Reproduction is amphimictic, by entomophily or self-pollination, and vegetative, by short rhizomes. Flowers are visited mainly by Hymenoptera, Diptera and Coleoptera (Lumer and Yost, 1995). Seed longevity is unknown. Seed production is greatly reduced in low light environments.

Associations

The monarch butterfly, Danaus plexippus, will lay eggs on V. nigrum, but larvae die (Casagrande and Dacy, 2001).

Environmental Requirements

V. nigrum, originally a western European Mediterranean species, has naturalized and spread in the continental climate of eastern North America, withstanding winter lows as extreme as -38°C and uniform annual precipitation over 1100 mm. It has a wide range of light and moisture tolerance. Habitats include meadows, successional shrublands, hedgerows, copses and woodland from rocky shores to more than 300 m altitude. The plant has a preference for lime-derived soils but is also found in granitic-based systems. Shore and roadside occurrences indicate salt tolerance.

Latitude/Altitude

Air Temperature

Rainfall

Rain Regime

Soil Tolerances

Soil drainage

• free
• seasonally waterlogged

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• light
• medium

Special soil tolerances

• saline
• shallow

Natural Enemies

Notes on Natural Enemies

One polyphagous Lepidoptera species, Nothris congressariella, is reported in the literature of insects associated with V. nigrum. However, eight other insect species have been reported on species of Vincetoxicum in Europe (Tewksbury et al., 2002) and are being considered for their potential as a biocontrol agent. There are no records of phytophagous insects on V. nigrum in North America. V. nigrum is one of the Vincetoxicum species susceptible to the European rust fungus Cronartium flaccidum, which causes cronartium rust and resin-top in conifers.

Means of Movement and Dispersal

Natural Dispersal

Seeds of V. nigrum are dispersed by wind, bearing the tuft of hairs, or coma, typical of the milkweed family. Seeds of the closely related species V. rossicum can travel up to 18 m at an average wind speed of 11.2 km/h from their release point, with 50% falling within 2.5 m (Cappuccino et al., 2002). Seeds may also float in water.

Accidental Introduction

It is possible that new introductions may occur as a result of seed travelling with agricultural commodities. For example species of Vincetoxicum may be transported by man, through garden cultivation or in hay sales. The presence of V. nigrum on transportation corridors suggests enhanced wind dispersal. Seeds have been observed in the trouser cuffs of hikers and hunters.

Intentional Introduction

Seed of V. nigrum are available to purchase on the internet in The Netherlands and Sweden and may be used for decorative purposes.

Pathway Vectors

Plant Trade

Impact Summary

Environmental Impact

Impact on Habitats

V. nigrum can successfully dominate susceptible natural areas producing dense patches which can crowd out native plant species. As a result the change in habitat structure can affects fauna populations and overall leads to a decrease in biodiversity. The ability of V. nigrum to dominate the woodland herbaceous layer raises concerns about forest regeneration. Conservation habitats, Christmas tree plantations, nursery crops and perennial crops such as alfalfa are affected (Uva et al., 1997).

Impact on Biodiversity

At least one endemic species, Astragalus robbinsii var. jesupii, is under pressure by an expanding population of V. nigrum. This species is extremely rare in its distribution and as such is endangered (U.S. Fish and Wildlife Service, 2009). Both V. nigrum and V. rossicum may have negative impact on the reproduction of the monarch butterfly. Danaus plexippus, as empty eggs have been found in the field. Experiments in field cages and in the laboratory indicate that larvae hatched from eggs oviposited on stems die in early instar stages (Casagrande and Dacy, 2001; DiTommaso and Losey, 2003).

Threatened Species

Social Impact

Persistent, intractable infestations of V. nigrum have discouraged gardeners in some cities of the northeastern USA. Large infestations have interfered with management of, and access to, amenity areas.

Risk and Impact Factors

Impact mechanisms

• Pest and disease transmission

Impact outcomes

• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Negatively impacts animal health
• Negatively impacts tourism
• Reduced amenity values
• Reduced native biodiversity

Invasiveness

• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Highly adaptable to different environments
• Highly mobile locally
• Proved invasive outside its native range
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc

Likelihood of entry/control

• Difficult/costly to control
• Highly likely to be transported internationally deliberately

Uses

Several Vincetoxicum species were investigated as rubber substitutes during World War II by the Canadian Department of Agriculture, however no published information is available. There is some interest in horticultural use of V. nigrum in Europe and this species is believed to have arrived in North America as a horticultural plant.

Similarities to Other Species/Conditions

V. nigrum may be confused with a number of closely related species in the genus Vincetoxicum.

In North America where their distributions overlap, V. nigrum is often confused with V. rossicum. However, flowers and fruits of V. rossicum tend to be smaller; flowers are 4-6 cm across, glabrous, creamy pale to dark maroon, on peduncles 2-5 cm long.

In Europe, V. hirundinaria has yellow-white flowers and only occasionally twines whereas V. fuscatum has brown flowers with short, erect stems. Lack of taxonomic agreement, numerous subspecies and evidence of hybridization all add to confusion between species.

Prevention and Control

Cultural Control

There are no reports of cultural control of V. nigrum, however grazing of the closely related V. hirundinaria by sheep has been investigated (Haeggström, 1990) and V. rossicum has been suppressed in cattle pastures in New York State, USA.

Mechanical Control

Mowing, pulling and other top destruction methods have poor long-term success for control of V. nigrum, as there is rapid regrowth from perennating buds. Effective timing of cutting, as fruit begin to enlarge, will prevent maturation of the seed crop and prevent successful recovery to form a new seed crop. Digging must remove the rhizomes and root crown.

Chemical Control

Triclopyr was found to be more effective at reducing the related species V. rossicum than has glyphosate (Lawlor and Raynal, 2002). A systemic herbicide must be used against this perennial plant.

Biological Control

Possibilities for biological control of V. nigrum and V. rossicum are currently being investigated (Tewksbury et al., 2002). Host-range studies at the University of Rhode Island (URI), USA, for Chrysolina aurichalcea ssp. asclepiadis have shown that this species is an unsuitable agent owing to the potential risk of attack on native North American Asclepias and Asteraceae (Weed and Casagrande, 2011).

In contrast, host-specificity tests conducted with more than 80 test plant species showed that the leaf-feeding moths Hypena opulenta and Abrostola asclepiadis are very host specific: successful larval development occurred only on species of Vincetoxicum. In 2014, mature H. opulenta larvae and pupae were successfully released on V. rossicum in Ottawa, Canada and the first release on V. nigrum was made in 2016. In 2016, H. opulenta had not yet been approved for release in the USA. Work on Chrysochus asclepiadeus did not show such a high host specificity level as for the two leaf feeding moths. Comparative host specificity studies are planed with various populations of C. asclepiadeus. Preliminary studies with the fruit fly Euphranta connexa indicate high host specificity. The potential of pathogens for biological control of V. nigrum has not yet been investigated. The chemical signature of Old World Asclepiadaceae may separate Vincetoxicum spp. from Asclepiadaceae species of the New World for effective host specificity.

IPM

Prevention and early eradication are the best control strategies for V. nigrum. Seed crops from upwind infestations must be managed to successfully prevent new infestations.

References

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Casagrande RA, Dacy J, 2001. Monarch Butterfly (Danus plexippus) oviposition on Black swallow-wort (Vincetoxicum nigrum). Rhode Island Natural History Survey, 8:2-3.

DiTommaso A, Losey JE, 2003. Oviposition selection and larval feeding by Monarch butterflies on two invasive swallow-wort species. Proceedings of the 57th Annual Meeting of the Northeastern Weed Science Society of America, 57:121.

Fournier P, 1977. Les quatres flores de la France. Vol. I, edition 2. Paris, France: +dition Lechevalier S.A.R.L.

Gleason HA, Cronquist A, 1991. Manual of Vascular Plants of Northeastern United States and adjacent Canada. Second edition. New York, USA: The New York Botanical Garden.

Hæggström CA, 1990. The influence of sheep and cattle grazing on wooded meadows in -land, SW Finland. Acta Botanica Fennica, 141:1-28.

Hegi G, 1927. Illustrierte flora von Mittle-Europa, Vol. 5. Munich, Germany: JF Lehmann.

Kaitera J, 1999. Cronartium flaccidum fruitbody production on Melampyrum spp. and some important alternate hosts to pine. European Journal of Forest Pathology, 29(6):391-398; 23 ref.

Kartesz JT, 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. In: Kartesz JR, Meachum CA, eds. Synthesis of the North American Flora, Version 1.0. Chapel Hill, North Carolina, USA: North Carolina Botanical Garden. CD-ROM.

Lawlor FM, Raynal DJ, 2002. Response of swallow-wort to herbicides. Weed Science, 50(2):179-185; 17 ref.

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Liede S, TSuber A, 2002. Circumscription of the genus Cynanchum (Apocynaceae-Asclepiadoideae). Systematic Botany, 27:789-800.

Lumer C, Yost SE, 1995. The reproductive biology of Vincetoxicum nigrum (L.) Moench (Asclepiadaceae), a Mediterranean weed in New York State. Bulletin of the Torrey Botanical Club, 122(1):15-23

Moore RJ, 1959. The dog-strangling vine Cynanchum medium, its chromosome number and its occurrence in Canada. Canadian Field-Naturalist, 73:144-147.

Pardi PN, 1933. Studi sulla cariologia dello Asclepiadaceae. Nuova Bot. Ital., 40:576-589.

Pringle JS, 1973. The spread of Vincetoxicum species (Asclepiadaceae) in Ontario. Canadian Field-Naturalist, 87:27-33.

Sheeley S, 1992. The distribution and life history characteristics of Swallow-wort (Vincetoxicum rossicum). M.S. thesis. Syracuse, New York, USA. State University of New York College of Environmental Science and Forestry.

Sheeley SE, Raynal DJ, 1996. The distribution and status of species of Vincetoxicum in eastern North America. Bulletin of the Torrey Botanical Club, 123(2):148-156; 47 ref.

Staerk D, Christensen J, Lemmich E, Duus J, Olsen C, Jaroszewski J, 2000. Cytotoxic activity of some phenanthroindolizidine N-oxide alkaloids from Cynanchum vincetoxicum. Journal of Natural Products, 63:1584-1586.

Tewksbury L, Casagrande R, Gassmann A, 2002. 16. Swallow-worts. In: Van Driesche R, Lyon S, Blossey B, Hoddle M, Reardon R, eds. Biological Control of Invasive Plants in the Eastern United States, United States Department of Agriculture Forest Service Publication FHTET-2002-04.

U.S. Fish and Wildlife Service, 2009. Jesup's milk-vetch (Astragalus robbinsii var. jesupii) spotlight species action plan. New Hampshire, USA: U.S. Fish and Wildlife Service, 7 pp. https://www.fws.gov/northeast/endangered/pdf/Jessup's%20milk-vetch%20SSAP.pdf

USDA-NRCS, 2016. The PLANTS Database. Baton Rouge, USA: National Plant Data Center. http://plants.usda.gov/

Uva RH, Neal JC, DiTomaso JM, 1997. Weeds of the Northeast. Ithaca, USA: Cornell University Press.

Weed AS, Casagrande RA, 2011. Evaluation of host range and larval feeding impact of Chrysolina aurichalcea asclepiadis (Villa): considerations for biological control of vincetoxicum in North America. Environmental Entomology, 40(6):1427-1436. http://esa.publisher.ingentaconnect.com/content/esa/envent/2011/00000040/00000006/art00014

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Contributors

28/12/2016 Updated by:

André Gassmann, CABI-CH, Switzerland

Distribution Maps

• = Present, no further details
• = Evidence of pathogen
• = Widespread
• = Last reported
• = Localised
• = Presence unconfirmed
• = Confined and subject to quarantine
• = See regional map for distribution within the country
• = Occasional or few reports

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