Invasive plants regulated in Montana (40 species, cited)

Invasive plants regulated in Montana

Montana lists 40 plants as noxious weeds under Montana Noxious Weed List (eff. June 21, 2019), ARM 4.5.201. The table below reproduces that list in full, showing each plant's status in the state's own words. Montana's list is an agricultural noxious-weed law, which governs control and spread on farmland and rights of way rather than what a nursery may sell.

Compiled from the rule itself, retrieved July 20, 2026. Law changes; if you spot a listing we have wrong or stale, tell us at [email protected].

Regulated and invasive are two different findings, and this page shows them separately. 36 of the 40 plants below carry both: Montana names them in statute and GRIIS lists them as invasive in the United States. The other 4 are regulated by Montana without appearing on that register. The reverse is far more common still: most plants GRIIS calls invasive are named in no state’s statute at all and are sold freely, so an absent chip is never a clean bill of health.

Plant	Scientific name	Status	Montana’s determination
Brazilian Waterweed	Egeria densa	Restricted Invasive	Montana lists Brazilian Waterweed under “Priority 3 regulated plant (not a listed noxious weed).”Plant instead: Star Sedge, Geyer's Sedge, Inland Sedge
Cheatgrass	Bromus tectorum	Restricted Invasive	Montana lists Cheatgrass under “Priority 3 regulated plant (not a listed noxious weed).”
Russian Olive	Elaeagnus angustifolia	Restricted Invasive	Montana lists Russian Olive under “Priority 3 regulated plant (not a listed noxious weed).”Plant instead: American Plum, Common Juniper, Pin Cherry
Waterthyme	Hydrilla verticillata	Restricted Invasive	Montana lists Waterthyme under “Priority 3 regulated plant (not a listed noxious weed).”Plant instead: Star Sedge, Geyer's Sedge, Inland Sedge
Broadleaved Pepperweed	Lepidium latifolium	Listed Invasive	Montana lists Broadleaved Pepperweed under “Priority 2A.”
Butter and Eggs	Linaria vulgaris	Listed Invasive	Montana lists Butter and Eggs under “Priority 2B.”
Canada Thistle	Cirsium arvense	Listed Invasive	Montana lists Canada Thistle under “Priority 2B.”
Common Reed	Phragmites australis	Listed	Montana lists Common Reed under “Priority 1A.”
Common St. Johnswort	Hypericum perforatum	Listed Invasive	Montana lists Common St. Johnswort under “Priority 2B.”
Common Viper's Bugloss	Echium vulgare	Listed Invasive	Montana lists Common Viper's Bugloss under “Priority 1B.”
Curly Pondweed	Potamogeton crispus	Listed Invasive	Montana lists Curly Pondweed under “Priority 2B.”
Dalmatian Toadflax	Linaria dalmatica	Listed Invasive	Montana lists Dalmatian Toadflax under “Priority 2B.”
Diffuse Knapweed	Centaurea diffusa	Listed Invasive	Montana lists Diffuse Knapweed under “Priority 2B.”
Dyer's Woad	Isatis tinctoria	Listed Invasive	Montana lists Dyer's Woad under “Priority 1A.”
Eurasian Watermilfoil	Myriophyllum spicatum	Listed Invasive	Montana lists Eurasian Watermilfoil under “Priority 2A.”
Field Bindweed	Convolvulus arvensis	Listed Invasive	Montana lists Field Bindweed under “Priority 2B.”
Flowering Rush	Butomus umbellatus	Listed Invasive	Montana lists Flowering Rush under “Priority 2A.”Plant instead: Showy Milkweed, Western Water Hemlock, Western Goldenrod
Gypsyflower	Cynoglossum officinale	Listed Invasive	Montana lists Gypsyflower under “Priority 2B.”
Hardheads	Acroptilon repens	Listed Invasive	Montana lists Hardheads under “Priority 2B.”
Hoary Alyssum	Berteroa incana	Listed Invasive	Montana lists Hoary Alyssum under “Priority 2B.”
Japanese Knotweed	Polygonum cuspidatum	Listed	Montana lists Japanese Knotweed under “Priority 1B.”
Japanese Knotweed	Fallopia japonica (potentially invasive weed)	Listed Invasive	Montana lists Japanese Knotweed under “Priority 1B.”
Leafy Spurge	Euphorbia esula	Listed Invasive	Montana lists Leafy Spurge under “Priority 2B.”
Lenspod Whitetop	Cardaria chalepensis	Listed	Montana lists Lenspod Whitetop under “Priority 2B.”
Meadow Hawkweed	Hieracium caespitosum	Listed Invasive	Montana lists Meadow Hawkweed under “Priority 2A.”
Medusahead	Taeniatherum caput-medusae	Listed Invasive	Montana lists Medusahead under “Priority 1A.”
North Africa Grass	Ventenata dubia	Listed Invasive	Montana lists North Africa Grass under “Priority 2A.”
Orange Hawkweed	Hieracium aurantiacum	Listed Invasive	Montana lists Orange Hawkweed under “Priority 2A.”
Oxeye Daisy	Leucanthemum vulgare	Listed Invasive	Montana lists Oxeye Daisy under “Priority 2B.”
Paleyellow Iris	Iris pseudacorus	Listed Invasive	Montana lists Paleyellow Iris under “Priority 2A.”Plant instead: Showy Milkweed, Western Water Hemlock, Western Goldenrod
Purple Loosestrife	Lythrum salicaria	Listed Invasive	Montana lists Purple Loosestrife under “Priority 1B.”Plant instead: Showy Milkweed, Western Water Hemlock, Western Goldenrod
Rush Skeletonweed	Chondrilla juncea	Listed Invasive	Montana lists Rush Skeletonweed under “Priority 1B.”
Scotch Broom	Cytisus scoparius	Listed Invasive	Montana lists Scotch Broom under “Priority 1B.”Plant instead: Silky Lupine, American Black Elderberry, Common Cowparsnip
Spotted Knapweed	Centaurea stoebe	Listed Invasive	Montana lists Spotted Knapweed under “Priority 2B.”
Stinking Willie	Senecio jacobaea	Listed Invasive	Montana lists Stinking Willie under “Priority 2A.”
Sulphur Cinquefoil	Potentilla recta	Listed Invasive	Montana lists Sulphur Cinquefoil under “Priority 2B.”
Tall Buttercup	Ranunculus acris	Listed	Montana lists Tall Buttercup under “Priority 2A.”
Tansy	Tanacetum vulgare	Listed Invasive	Montana lists Tansy under “Priority 2B.”
Whitetop	Cardaria draba	Listed Invasive	Montana lists Whitetop under “Priority 2B.”
Yellow Star-Thistle	Centaurea solstitialis	Listed Invasive	Montana lists Yellow Star-Thistle under “Priority 1A.”

What the tags mean

Prohibited Restricted Listed

A legal status. Montana names the plant in statute. Under a nursery rule that means it may not be sold, propagated, or moved; under an agricultural weed law it means landowners must control it. The cited rule says which, in Montana’s own words, in the last column.

Invasive

An ecological finding, and a different question from the law. GRIIS — the Global Register of Introduced and Invasive Species — lists the plant as invasive in the United States. Most invasive plants carry no state listing at all and are sold freely, so a plant without this tag is not thereby safe, and a plant without a legal chip is not thereby harmless.

Where this comes from

Montana listings: Montana Noxious Weed List (eff. June 21, 2019), ARM 4.5.201. Read the rule.
Invasive status: GRIIS, the Global Register of Introduced and Invasive Species, via GBIF. A scientific register with no legal force; it is cited separately from the statute above because the two disagree far more often than they agree.
Status wording: Each determination is written as a sentence, with Montana’s own term for the plant reproduced verbatim inside it. The Prohibited / Restricted / Listed chips are Ezina’s normalisation across 42 states and are not the legal term.
Nativity: USDA PLANTS county distribution layer, surfaced through the county checker.

Regulated next door, but not in Montana

Plants that two or more states bordering Montana regulate, and Montana does not. A listing is a legal act rather than an ecological one, so a plant can be a documented problem here and still be sold here.

Absinthium Artemisia absinthium regulated in North Dakota, South Dakota
Field Sowthistle Sonchus arvensis regulated in Idaho, South Dakota
Nodding Plumeless Thistle Carduus nutans regulated in Idaho, North Dakota

Questions

What plants are illegal to sell in Montana?

Montana's list is an agricultural noxious-weed law, which governs control and spread on farmland and rights of way rather than what a nursery may sell. 40 plants are named under Montana Noxious Weed List (eff. June 21, 2019), ARM 4.5.201. A noxious-weed listing does not automatically ban nursery sale, so check the rule itself before assuming a plant cannot be bought or sold.

Is my plant invasive in Montana?

Search the table on this page, or enter the plant's name in Ezina's checker to get its Montana status alongside whether USDA records it as native to your specific county. Every answer links the record it came from.

Does a plant missing from this list mean it is safe to plant in Montana?

No. This page reproduces what Montana regulates, and a state list is a legal instrument rather than an ecological verdict. Plenty of plants spread aggressively without ever being listed, and states add species years after the problem is documented.

Grow natives easily with Ezina

How it works

We provide the tools you need to succeed.

The Ezina app identifying a plant: a live camera view framing pink coneflowers, with Plant, Disease/Insect, and Both scan modes.

010.1Identify

Add a plant

Snap a photo or type the name. The app pulls 4,000+ species from peer-reviewed horticulture data and starts a care plan tailored to your zone, the local weather, and the time of year.

The Ezina app’s care screen: water needs showing status Okay, last watered 12 days ago, a suggested volume, and a treatment section.

010.2Care

Get a care plan

A schedule built from local rain, temperature, and sun, not a fixed weekly cadence. You get a single notification when a plant actually needs water. Easily add treatments for diseases and pests.

The Ezina Dig planner: a starting-plan site map with suggested garden beds you can draw with your finger.

010.3Plan

Explore new options

Our garden planner Dig helps you understand what works best for your location and makes suggestions based off your long term goals.

Add a plant

Snap a photo or type the name. The app pulls 4,000+ species from peer-reviewed horticulture data and starts a care plan tailored to your zone, the local weather, and the time of year.

Get Ezina for your garden Explore Ezina

Compiled from peer-reviewed research, USDA documentation,
and direct scientific observation across the 48 contiguous states.