Flower profile

Black swallow-wort

Vincetoxicum nigrum

Introduced in the lower 48

Black swallow-wort is a wildflower that USDA PLANTS lists as introduced in the lower 48 states. It's on our flower lists for 2 states, and across the U.S. it's most often seen in bloom in May–August.

21states

2of our state lists

4,138U.S. sightings*

*iNaturalist research-grade observations, as of October 17, 2026.

On our lists for: Massachusetts, Rhode Island

🚫

Regulated invasive plant in Massachusetts. It's on that state' official invasive plant list (Massachusetts: Prohibited plant (sale, import and propagation banned) (as Cynanchum louiseae)). Please don't plant or share it there. ^{MA Prohibited Plant List}

Quick look

Vincetoxicum nigrum, a species in the family Apocynaceae, also known as black swallow-wort, Louise's swallow-wort, or black dog-strangling vine, is a species of plant that is native to Europe and is found primarily in Italy, France, Portugal, and Spain. It is an invasive plant species in the northeastern United States, parts of the Midwest, southeastern Canada, and California.
From Wikipedia's article Vincetoxicum nigrum, CC BY-SA 4.0.

It belongs to the Apocynaceae family. ^iNaturalist
USDA PLANTS describes it as an herb (forb) / a vine with a perennial life cycle. ^{USDA PLANTS}
USDA PLANTS lists it as introduced in the lower 48 states and records it in 21 states. ^{USDA PLANTS}
NatureServe lists it as not native to Massachusetts and Rhode Island. ^NatureServe
In Massachusetts, most iNaturalist sightings of it in flower come in May–July. ^iNaturalist
iNaturalist has 2,207 research-grade sightings of it in Massachusetts, ranking #61 among the 110 flowers on our Massachusetts list. ^iNaturalist
iNaturalist has 158 research-grade sightings of it in Rhode Island, ranking #97 among the 110 flowers on our Rhode Island list. ^iNaturalist

State flower gift ideas

This one is a regulated invasive plant, so here are state flower gifts instead.

🌱 Sample spot. Handmade gift picks from independent shops will appear here once our shop partnership is approved. These cards are placeholders, not real products.

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State flower print
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Birth-flower necklace
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Wildflower seed favors
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Botanical tea towel
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Pressed-flower frame
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Flower-garden mug
Gift pick coming soon

When does it bloom?

Flowering records by month across the U.S. (iNaturalist research-grade observations marked “Flowering”) (459 records)

Bloom time in each of our 2 states

State	Type	Peak bloom	Sightings*
Massachusetts	Introduced	May–July	2,207
Rhode Island	Introduced	few records	158

Conservation status

Federal (U.S. ESA): Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. ^{USFWS ECOS}
NatureServe global: GNR Not yet ranked worldwide. ^NatureServe
Massachusetts: Not listed Not on Massachusetts Endangered Species Act list (321 CMR 10.90). NatureServe: SNA, not applicable (usually because it isn't native there) in Massachusetts. ^{MESA list}
Rhode Island: Not listed Not on Rhode Island Rare Plants 2016 (RI Natural History Survey, from the RI Wildlife Action Plan; informational, Rhode Island has no state plant-protection listing law). NatureServe: SNA, not applicable (usually because it isn't native there) in Rhode Island. ^{RI rare plants 2016}
Rare elsewhere: No other U.S. state ranks it S1, S2, SH or SX.

Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.

Can you eat it?

For peopleNot well documented

None of the sources we checked (NC State Extension (no page for this plant), USDA PLANTS) say whether it's edible or poisonous for people.

For petsNot well documented

It isn't on the ASPCA plant list.

🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.

Where does it grow?

USDA PLANTS records black swallow-wort in 21 states.

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recorded by USDA PLANTS on our state lists not recorded

See the full list of states

California, Connecticut, Illinois, Indiana, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, Wisconsin.

Massachusetts counties with USDA records: Barnstable, Berkshire, Bristol, Essex, Franklin, Hampden, Hampshire, Middlesex, Norfolk, Plymouth, Suffolk, Worcester.

Rhode Island counties with USDA records: Bristol, Newport, Washington.

More Massachusetts flowers

Common milkweed

Asclepias syriaca

Native

🌼 Blooms in MA: June–July

Butterfly milkweed

Asclepias tuberosa

Native

🌼 Blooms in MA: June–September

Lesser periwinkle

Vinca minor

Introduced

🌼 Blooms in MA: March–May

Sources

USDA, NRCS. PLANTS Database, profile CYLO11.
iNaturalist, Vincetoxicum nigrum: taxonomy, research-grade observation counts and “Flowering” annotations, retrieved October 17, 2026.
Wikipedia, Vincetoxicum nigrum (lead quoted under CC BY-SA 4.0).
Massachusetts: Massachusetts Endangered Species Act list (321 CMR 10.90).
Massachusetts: Massachusetts Prohibited Plant List (MDAR) (Text from MDAR's 2023 scientific-name PDF (mass.gov blocks automated downloads); 2024-2026 additions listed on the mass.gov page: Alnus glutinosa, Pyrus calleryana, Miscanthus sinensis, Aralia elata, Rhodotypos scandens, Symplocos paniculata.).
Rhode Island: Rhode Island Rare Plants 2016 (RI Natural History Survey, from the RI Wildlife Action Plan; informational, Rhode Island has no state plant-protection listing law).
USFWS, ECOS species database (ESA listing check), October 17, 2026.
NatureServe Explorer, Vincetoxicum nigrum (global and state ranks).
Edibility and toxicity: no source found (marked "not well documented").
Photo: Michael Pirrello via iNaturalist · CC BY 4.0 · resized.