Bloomipedia
Black swallow-wort (Vincetoxicum nigrum)
Photo: Michael Pirrello via iNaturalist · CC BY 4.0 · resized

Flower profile

Black swallow-wort

Vincetoxicum nigrum

Black swallow-wort (Vincetoxicum nigrum) is a vine in the Apocynaceae family, introduced in the lower 48 states, blooming mostly May–July across the U.S.

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–July.

21states where USDA records it
2Bloomipedia state lists include it
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.

  • 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 June–July. iNaturalist
  • iNaturalist has 2,207 research-grade sightings of it in Massachusetts, ranking #64 among the 188 flowers on our Massachusetts list. iNaturalist
  • iNaturalist has 158 research-grade sightings of it in Rhode Island, ranking #100 among the 164 flowers on our Rhode Island list. iNaturalist

When does it bloom?

Flowering records by month across the U.S. (iNaturalist research-grade observations marked “Flowering”) (459 records)
Bloom time in the 2 states whose Bloomipedia list includes it
StateTypePeak bloomSightings*
MassachusettsIntroducedJune–July2,207
Rhode IslandIntroducedfew records (12)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.

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.

Names, range and relatives

Native status by region (USDA PLANTS): Canada: Introduced; Lower 48 states: Introduced.

County records: USDA PLANTS lists it in 90 counties across 15 states; the most are in New York (24), Massachusetts (12), Pennsylvania (10).

More from the Apocynaceae family (28 on Bloomipedia; most observed first): Common milkweed, Butterfly milkweed, Lesser periwinkle, Swamp milkweed, Greater periwinkle, Green antelopehorns, Antelopehorn milkweed, Showy milkweed.

More Massachusetts flowers

Common milkweed (Asclepias syriaca)

Common milkweed

Asclepias syriaca

Native

🌼 Blooms in MA: June–July
Lesser periwinkle (Vinca minor)

Lesser periwinkle

Vinca minor

Introduced

🌼 Blooms in MA: April–May
Butterfly milkweed (Asclepias tuberosa)

Butterfly milkweed

Asclepias tuberosa

Native

🌼 Blooms in MA: June–August

Sources