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Status
Black Swallow-wort is a rare non-native milkweed that has the potential to become an invasive species in Maryland. Black Swallow-wort is native to southwestern Europe and was originally introduced to the United States in the 1800s. According to an article published in the Boston Globe, "It all started in the mid-1800s [1854, to be exact] when the black swallow-wort, a perennial, herbaceous vine native to southern Europe, was first cultivated in greenhouses in Ipswich and at the Harvard Botanical Garden in Cambridge. When, a short time later, the vine was discovered growing wild in Cambridge, it was assumed it had escaped from the Harvard greenhouse." Since then Black Swallow-wort has invaded most of New England and many of the Great Lake states. Maryland is at the southern edge of its non-native range in the United States. The Minnesota Natural Resources Conservation Service writes, "Black swallow-wort spreads long distances by seed and rhizomes. Thick infestations in full sun can produce 2,000 seeds per square meter. One seed produces one to four embryos, which greatly increases the likelihood of seed survival and establishment. Rhizomes can form extensive patches in clumps of several to many stems that crowd out the native vegetation. Stands can eventually cover several acres of land."
Most sources state that Black Swallow-wort is a plant of upland habitats but a population found in Talbot County is growing only a few yards away from a brackish tidal creek!
Description
Black Swallow-wort can be confused with a few of our rare native milkweed vines like Maroon Carolina Milkvine (Matelea carolinensis) and Climbing Milkvine (Matelea obliqua). To differentiate between Black Swallow-wort and our native species of Matelea, first look at the flowers. The flowers are typically the same color, a rich purplish brown, but the flower size is very different. Our native Mateleas have much larger flowers than Black Swallow-wort. The petals of Black Swallow-wort range from 1.5 mm to 4.5 mm long while the petals of our native Mateleas range from 6 mm to 18 mm (Weakley, 2015). The leaves of the two genera are also different. The leaves of Black Swallow-wort are smaller and more lanceolate than the larger, broader and more rounded leaves of our native Matelea species.
When not in flower Black Swallow-wort may also be confused with Honey Vine (Cynanchum laeve) another species of vining milkweed native to Maryland. Honey Vine has white flowers which makes identification easy but if flowers are lacking you need to look at the base of the leaves. The leaves of Honey Vine have extreme cordate bases which the leaves of Black Swallow-wort lack.
Relationships
Unfortunately, Black Swallow-wort can also cause harm to Monarch butterflies. According to the Monarch Joint Venture web site, "Studies have shown that female monarchs will lay eggs on black swallow-wort, even when it is growing in the same field as common milkweed (Casagrande and Dacey 2007). Laboratory tests show that monarch caterpillars cannot feed on black or pale swallow-wort plants. Thus, swallow-worts may act as a 'sink' for monarchs; caterpillars from eggs laid on these invasive plants will not survive, and are essentially wasted." The Casagrande and Dacey paper states that in some cases over 20% of the Monarchs being monitored in a semi-controlled environment decided to lay their eggs on Black Swallow-wort instead of Common Milkweed! In their paper published in the journal Environmental Entomolgy, 2007, the authors state in their conclusion, "It is clear that, at least in southern Rhode Island, monarch butterflies oviposit on Vincetoxicum species, and they lay a higher proportion of eggs on these dead-end hosts when [Common Milkweed] plants are relatively rare. To date, there is no evidence that monarchs are evolving an ability to survive on these exotic plants. Rather, Vincetoxicum species seem to be functioning as evolutionary traps (Schlapfer et al. 2005). Because no larvae survived from eggs laid on Vincetoxicum, there should be selection pressure against those adults making this oviposition 'mistake.' However, after over a century of exposure to these exotic plants, this behavior persists. This behavioral trait may be related to the fact that [Honey Vine] serves as an important host for monarch butterflies in parts of the southeastern United States (Yeargan and Allard 2005). Vincetoxicum and Cynanchum are closely related genera, possibly sharing ovipositional stimulants for monarch butterflies. Successful reproduction on C. laeve may offset selective effects of oviposition on Vincetoxicum species."
Seasonality Snapshot
Source: Wikipedia
| Vincetoxicum nigrum | |
|---|---|
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| [1] | |
Scientific classification 
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| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Gentianales |
| Family: | Apocynaceae |
| Genus: | Vincetoxicum |
| Species: | V. nigrum
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| Binomial name | |
| Vincetoxicum nigrum (L.) Moench
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| Synonyms | |
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Vincetoxicum nigrum, a species in the family Apocynaceae, also known as black swallow-wort,[2] Louise's swallow-wort,[3] or black dog-strangling vine,[4] is a species of plant that is native to Europe and is found primarily in Italy, France, Portugal, and Spain.[5] It is an invasive plant species in the northeastern United States, parts of the Midwest, southeastern Canada, and California. In 2020, wild plants were found in Timaru, New Zealand.[6]
Description
[edit]Vincetoxicum nigrum is a perennial, herbaceous vine bearing ovate leaves with pointed tips. The leaves are 3–4 inches (7.6–10.2 cm) long, and 2–3 inches (5.1–7.6 cm) wide, occurring in pairs on the stem. The flowers have five petals, and are star-shaped with white hairs. The flowers range in color from dark purple to black. The fruit of Vincetoxicum nigrum is a slender, tapered follicle that ranges in color from green through light brown and is tightly packed with seeds, each bearing a fluffy pappus to allow distribution by the wind.[5]
Habitat
[edit]Vincetoxicum nigrum tends to grow in upland areas and is tolerant to variable light, salt, and moisture levels. In the United States, the vine is often found in abandoned fields, hedgerows, brushy areas, woodlands, river banks, transportation corridors, quarries, agricultural fields, and gardens. In gardens, the plant is seen as a fast-growing weed.[5]
Reproduction
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Vincetoxicum nigrum emerges from an underground stem in the spring, and flowers during June and July. Vincetoxicum nigrum is self-pollinating, and follicles form throughout the summer. The number of follicles formed is directly linked to the amount of light the plant receives. If there is a lower level of light, then there are fewer follicles compared to a plant exposed to a higher level of light. The seeds begin to be released by mid-August, and continue to be dispersed by air currents into early October.
Each seed is polyembryonic and contains about one to four embryos per seed, increasing Vincetoxicum nigrum's proliferation. Seeds have delicate fibrous "parachutes" used in wind dispersal over long distances. In addition to seeds for reproduction, Vincetoxicum nigrum also uses rhizomes as a method of propagation, meaning that the plant clones itself underground and produces new plants. After seed dispersal, the plant dies to the ground in the winter, reappearing in the spring.[5]
Invasiveness
[edit]
The first sighting of Vincetoxicum nigrum in North America was recorded in Ipswich, Massachusetts in 1854. In 1864, a plant collector recorded that it was "escaping from the botanical garden where it is a weed promising to be naturalized". Vincetoxicum nigrum escaped from a garden in the Cambridge area of Massachusetts and naturalized in the surrounding states and is still spreading today.[5] Massachusetts[7] and New York[8] classify the plant as an invasive species. Beyond the northeastern US, the plant has been reported in Wisconsin and California.[5]
Ecological implications
[edit]In the United States and Canada, Vincetoxicum nigrum is a threat to native species because it crowds them out. For example, it can completely replace a field of native goldenrod.[9] Crowding out other species results in a reduced habitat for wildlife, which may become endangered because they can no longer find their optimal habitat.
Vincetoxicum nigrum threatens the rare limestone pavement barren ecosystems by crowding out plants that the native wildlife needs to survive. It may also decrease bird presence in grasslands, which may in turn cause certain insect species populations to increase.
In Vermont, Vincetoxicum nigrum crowds out the endangered species Jesup's milk vetch (Astragalus robbinsii var. jesupii). In Rhode Island, Vincetoxicum nigrum has been reported as reducing the effectiveness of electric fences, which may allow livestock to be put into danger or lost.[10]
In addition, Vincetoxicum nigrum crowds out a species of milkweed that monarch butterflies use as their larval food plant. Thus, the spread of this plant threatens populations of monarch butterflies. Overall, Vincetoxicum nigrum reproduces very prolifically, and can easily take over various habitats in a short time. Most of the possible implications of Vincetoxicum nigrum's changing the structure of various ecosystems have not yet been studied.[5]
Management
[edit]There are four methods of management that can possibly be used for the management of Vincetoxicum nigrum. These methods are chemical, manual, mechanical, and biological. Only the chemical, manual, mechanical methods are actually used in the United States and Canada. The biological method may be used in the future.[11] Overall, early detection and removal is the best management strategy.
Chemical
[edit]The best chemical management of Vincetoxicum nigrum is through the use of systemic herbicides which prevent seeds from being viable. Garlon 4 (triclopyr) and RoundUp Pro (glyphosate) are the main systemic herbicides that are used to control the vine. The systemic herbicide is most effective when sprayed on the plant after flowering has begun. If the herbicide is used after follicles have formed, it is less effective because viable seeds may still form. The most effective treatment using systemic herbicides is through a cut stem application, consisting of applying the chemical to the recently-cut stems of the swallow-wort vines.[5]
Manual
[edit]Manual management is the removal of Vincetoxicum nigrum from the ground by digging up its rhizomes so that the plant cannot reproduce.[5] The vine has an extensive rhizome system which must be completely removed to prevent new shoots from growing. Trying to remove the vine by pulling will often cause the plant to detach from its rhizome, allowing the vine to continue to grow new shoots. Seed pods must be disposed of carefully, to avoid inadvertently spreading the seeds to new areas.
Mechanical
[edit]Mechanical management is the mowing down of Vincetoxicum nigrum. This method does not stop growth, but it does stop seed crops. No seed crop means that the plant has no offspring.[5]
Biological
[edit]Biological management is the use of the vine's natural enemies to stop the spread and diminish the population of Vincetoxicum nigrum. In the United States, Vincetoxicum nigrum has no natural enemies, but in its native Europe, certain caterpillars, beetles, and diseases attack the plant. Researchers at Cornell University and the USDA have investigated the use of natural enemies as a way to control the plant. The use of natural enemies is controversial, because the implications of adding more non-native species to threatened areas is unknown.[11] In 2014 Hypena caterpillars were released in Ontario, Canada to help control Vincetoxicum's spread.[12]
References
[edit]- ^ 1913 illustration from Britton & Brown, Illustrated flora of the northern states and Canada, PD US, Vincetoxicum nigrum
- ^ BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-06-26. Retrieved 2014-10-17.
- ^ "Classification for Kingdom Plantae Down to Species Cynanchum louiseae Kartesz & Gandhi". USDA Natural Resources Conservation Service. 2008-05-30. Retrieved 2008-05-30.
- ^ "Black dog-strangling vine". Center for Invasive Species and Ecosystem Health and USDA APHIS PPQ. 2010-05-24. Retrieved 2011-07-24.
- ^ a b c d e f g h i j "Black Swallow-Wort". Fact Sheets. Plant Conservation Alliance, Alien Plant Working Group. 2006-06-27. Archived from the original on 2017-07-16. Retrieved 2008-05-30.
- ^ "Black Swallow-Wort (Vincetoxicum nigrum)". iNaturalist NZ. 29 November 2020.
- ^ Sally Kerans (May 31, 2007). "Invasive plants: Old standards get bad name". Danvers Herald. Archived from the original on October 24, 2013.
- ^ "Interim List of Invasive Plant Species in New York State". Advisory Invasive Plant List. New York State Department of Environmental Conservation. Archived from the original on 12 May 2013. Retrieved 1 June 2013.
- ^ "| Concord, MA".
- ^ "Swallow-Worts". The Bugwood Network, USDA Forest Service & USDA APHIS PPQ. The University of Georgia - Warnell School of Forest Resources and College of Agricultural and Environmental Sciences - Dept. of Entomology. 2003-11-05. Retrieved 2008-05-30.
- ^ a b Ramanujan, Krishna (2006-02-01). "Wanted by Cornell and USDA researchers: A natural enemy to curb two invasive, poisonous vines". Cornell Chronicle Online. Ithaca, NY: Cornell University. Retrieved 2008-05-30.
- ^ Campbell, Don; Ali, Dominic (September 9, 2014). "Hungry caterpillar? U of T researchers enlist tiny ally in fight against invasive plant species". University of Toronto. U of T News. Retrieved 2018-07-17.
After eight years of research, the very first field releases of Hypena caterpillars in North America were done at several DSV-infested sites throughout Ontario.
External links
[edit]
Media related to Vincetoxicum nigrum at Wikimedia Commons
- Forest Health Staff. "Black Swallow-wort Vincetoxicum nigrum" (PDF). Weed of the Week. USDA Forest Service. Retrieved 2011-06-29.