Flower profile

Poison hemlock

Conium maculatum

Introduced in the lower 48

Poison hemlock is a wildflower that USDA PLANTS lists as introduced in the lower 48 states. It's on our flower lists for 12 states, and across the U.S. it's most often seen in bloom in April–July.

46states

12of our state lists

39,200U.S. sightings*

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

On our lists for: California, Delaware, Indiana, Iowa, Kansas, Kentucky, Missouri, Nebraska, Ohio, Oregon, Pennsylvania, Washington

🚫

Regulated invasive plant in Pennsylvania, Washington, Oregon, Kentucky, Indiana and Iowa. It's on those states' official invasive plant lists (Pennsylvania: Class B noxious weed; Washington: Class B noxious weed (control required in listed regions); Oregon: "B" noxious weed (sale and transport prohibited); Kentucky: Noxious weed (controlled on state highways under KRS 176.051); Indiana: Prohibited invasive plant (no sale, gifting or planting); Iowa: Secondary noxious weed). Please don't plant or share it there. ^{PA noxious weed list WAC 16-750 OAR 603-052-1200 KRS 176.051 312 IAC 18-3-25 Iowa Code § 317.1A}

Quick look

Conium maculatum, commonly known as hemlock or poison hemlock, is a highly poisonous flowering plant and a nitrophile weed species in the carrot family Apiaceae.
From Wikipedia's article Conium maculatum, CC BY-SA 4.0.

It belongs to the Apiaceae family. ^iNaturalist
USDA PLANTS describes it as an herb (forb) with a biennial life cycle. ^{USDA PLANTS}
USDA PLANTS lists it as introduced in the lower 48 states and records it in 46 states. ^{USDA PLANTS}
In California, most iNaturalist sightings of it in flower come in April–September. ^iNaturalist
In Ohio, most iNaturalist sightings of it in flower come in May–June. ^iNaturalist
iNaturalist has 16,110 research-grade sightings of it in California, ranking #43 among the 110 flowers on our California list. ^iNaturalist
iNaturalist has 2,939 research-grade sightings of it in Ohio, ranking #56 among the 109 flowers on our Ohio list. ^iNaturalist
iNaturalist has 2,549 research-grade sightings of it in Pennsylvania, ranking #82 among the 111 flowers on our Pennsylvania 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
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When does it bloom?

Flowering records by month across the U.S. (iNaturalist research-grade observations marked “Flowering”) (5,804 records)

Bloom time in each of our 12 states

State	Type	Peak bloom	Sightings*
California	Introduced	April–September	16,110
Ohio	Introduced	May–June	2,939
Pennsylvania	Introduced	May–June	2,549
Washington	Introduced	May–July	2,360
Oregon	Introduced	May–July	1,662
Kentucky	Introduced	May–June	989
Indiana	Introduced	May–June	790
Missouri	Introduced	May–June	730
Iowa	Introduced	May–July	537
Nebraska	Introduced	May–June	471
Kansas	Introduced	May–July	456
Delaware	Introduced	May–June	154

Conservation status

Federal (U.S. ESA): Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. ^{USFWS ECOS}
NatureServe global: G5 Secure worldwide. ^NatureServe
California: Not listed Not on California state-listed endangered, threatened and rare plants (14 CCR § 670.2), per CDFW's CNDDB list (July 2026). NatureServe: SNA, not applicable (usually because it isn't native there) in California. ^{CNDDB listed plants (July 2026)}
Ohio: Not listed Not on Ohio endangered and threatened plants (Ohio Adm. Code 1501:18-1-03, eff. Dec. 26, 2024). NatureServe: SNA, not applicable (usually because it isn't native there) in Ohio. ^{OAC 1501:18-1-03}
Pennsylvania: Not listed Not on Pennsylvania classified native plants (17 Pa. Code Ch. 45, Subchapter B, as amended 2023). NatureServe: SNA, not applicable (usually because it isn't native there) in Pennsylvania. ^{17 Pa. Code Ch. 45}
Washington: No list Washington has no state law listing endangered or threatened plants (the Washington Natural Heritage Program's rare plant list isn't regulatory), so we show NatureServe's Washington ranks instead. NatureServe: SNA, not applicable (usually because it isn't native there) in Washington.
Oregon: Not listed Not on Oregon endangered and threatened plants (OAR 603-073-0070). NatureServe: SNA, not applicable (usually because it isn't native there) in Oregon. ^{OAR 603-073-0070}
Kentucky: Not listed Not on Kentucky endangered and threatened plant lists (400 KAR 3:040, eff. 2026). NatureServe: SNA, not applicable (usually because it isn't native there) in Kentucky. ^{400 KAR 3:040}
Indiana: No list Indiana has no state law listing endangered or threatened plants (the DNR keeps a rare plant list, but it isn't regulatory), so we show NatureServe's Indiana ranks instead. NatureServe: SNA, not applicable (usually because it isn't native there) in Indiana.
Missouri: Not listed Not on Missouri Wildlife Code endangered species (3 CSR 10-4.111), plants. NatureServe: SNA, not applicable (usually because it isn't native there) in Missouri. ^{3 CSR 10-4.111}
Iowa: Not listed Not on Iowa endangered, threatened and special concern plants (Iowa Admin. Code r. 571-77.3). NatureServe: SNA, not applicable (usually because it isn't native there) in Iowa. ^{IAC 571-77.3}
Nebraska: Not listed Not on Nebraska threatened and endangered species (163 Neb. Admin. Code ch. 4, § 004). NatureServe: SNA, not applicable (usually because it isn't native there) in Nebraska. ^{163 NAC 4-004}
Kansas: No list Kansas's endangered and threatened list (K.A.R. 115-15-1) covers animals only, so we show NatureServe's Kansas ranks for plants. NatureServe: SNA, not applicable (usually because it isn't native there) in Kansas.
Delaware: Not listed Not on Rare and Uncommon Plants of Delaware (DNREC, 2024; informational, Delaware has no state plant-protection list). NatureServe: SNA, not applicable (usually because it isn't native there) in Delaware. ^{DE rare plants 2024}
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 peoplePoisonous to people

NC State Extension lists it as poisonous to humans (severity: high). Poisonous parts: bark, flowers, fruits, leaves, roots, sap/juice, seeds, stems. Symptoms they list: “HIGHLY TOXIC, MAY BE FATAL IF EATEN! Delivery by ingestion. Salivation, vomiting, diarrhea, muscular weakness, paralysis, nervousness, trembling, dilation of pupils, weak pulse, convulsions, coma. People with highly sensitive skin may experience contact…” ^{NC State Extension}

For petsToxic to dogs, cats and horses

ASPCA's entry “Poison Hemlock” (Conium maculatum) lists it as toxic to dogs, cats and horses. Signs include: Agitation, tremors, drooling, diarrhea, paralysis, death Credit: William & Wilma Follette @ USDA-NRCS PLANTS Database / USDA NRCS. 1992. Western wetland flora: Field office guide to plant species… ^ASPCA

🌿 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 poison hemlock in 46 states plus Washington, D.C.

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recorded by USDA PLANTS on our state lists not recorded

See the full list of states

Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming; District of Columbia.

California counties with USDA records: Alameda, Butte, Contra Costa, Del Norte, Glenn, Humboldt, Kern, Los Angeles, Marin, Mendocino, Merced, Modoc, Mono, Monterey, Napa, Nevada, Orange, Placer, Plumas, Riverside, Sacramento, San Bernardino, San Diego, San Francisco, San Joaquin, San Luis Obispo, San Mateo, Santa Barbara, Santa Clara, Santa Cruz, Shasta, Siskiyou, Solano, Sonoma, Tehama, Tuolumne, Ventura, Yolo.

Ohio counties with USDA records: Adams, Ashland, Ashtabula, Auglaize, Butler, Champaign, Clark, Clinton, Coshocton, Crawford, Cuyahoga, Darke, Delaware, Erie, Fairfield, Fayette, Greene, Hamilton, Highland, Holmes, Knox, Lake, Lawrence, Licking, Lorain, Madison, Meigs, Mercer, Miami, Monroe, Montgomery, Ottawa, Pickaway, Pike, Putnam, Richland, Ross, Scioto, Stark, Trumbull, Union, Warren, Washington, Wayne, Williams, Wood, Wyandot.

Pennsylvania counties with USDA records: Adams, Allegheny, Beaver, Bedford, Berks, Blair, Bradford, Bucks, Centre, Chester, Crawford, Cumberland, Delaware, Erie, Franklin, Fulton, Greene, Huntingdon, Juniata, Lackawanna, Lancaster, Lehigh, Luzerne, Mifflin, Montgomery, Montour, Northampton, Philadelphia, Potter, Snyder, Tioga, Washington, Wayne, Wyoming, York.