Bloomipedia
Lambert's locoweed (Oxytropis lambertii)
Photo: Larry Jensen via iNaturalist · CC BY 4.0 · resized

Flower profile

Lambert's locoweed

Oxytropis lambertii

Lambert's locoweed (Oxytropis lambertii) is a flowering plant in the Fabaceae family, native in the lower 48 states, blooming mostly May–July across the U.S.

Native in the lower 48

Lambert's locoweed is a wildflower that USDA PLANTS lists as native in the lower 48 states. It's on our flower lists for 4 states, and across the U.S. it's most often seen in bloom in May–July.

15states where USDA records it
4Bloomipedia state lists include it
6,933U.S. sightings*

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

On our lists for: Colorado, Nebraska, North Dakota, South Dakota

Quick look

Oxytropis lambertii commonly known as purple locoweed, Colorado locoweed, Lambert's crazy weed, or Lambert’s Locoweed is a species of flowering plant in the legume family.

  • It belongs to the Fabaceae family. iNaturalist
  • USDA PLANTS describes it as an herb (forb) with a perennial life cycle. USDA PLANTS
  • USDA PLANTS lists it as native in the lower 48 states and records it in 15 states. USDA PLANTS
  • NatureServe lists it as native to Colorado, North Dakota, South Dakota and Nebraska. NatureServe
  • In Colorado, most iNaturalist sightings of it in flower come in May–July. iNaturalist
  • USDA PLANTS lists its flower color as red. USDA PLANTS
  • USDA PLANTS gives its bloom period as mid spring. USDA PLANTS
  • USDA PLANTS lists a mature height of about 1.4 ft. USDA PLANTS
  • iNaturalist has 3,838 research-grade sightings of it in Colorado, ranking #30 among the 160 flowers on our Colorado list. iNaturalist
  • iNaturalist has 343 research-grade sightings of it in North Dakota, ranking #12 among the 116 flowers on our North Dakota list. iNaturalist
  • iNaturalist has 262 research-grade sightings of it in South Dakota, ranking #52 among the 126 flowers on our South Dakota list. iNaturalist

When does it bloom?

Flowering records by month across the U.S. (iNaturalist research-grade observations marked “Flowering”) (354 records)
Bloom time in the 4 states whose Bloomipedia list includes it
StateTypePeak bloomSightings*
ColoradoNativeMay–July3,838
North DakotaNativefew records (49)343
South DakotaNativefew records (15)262
NebraskaNativefew records (13)165

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
Colorado
No list Colorado has no state law listing endangered or threatened plants, so we show NatureServe's Colorado ranks instead. NatureServe: S5, secure in Colorado.
North Dakota
No list North Dakota has no state law listing endangered or threatened plants, so we show NatureServe's North Dakota ranks instead. NatureServe: SNR, not yet ranked in North Dakota.
South Dakota
No list South Dakota's endangered and threatened list (ARSD 41:10:02) covers animals only, so we show NatureServe's South Dakota ranks for plants. NatureServe: SNR, not yet ranked in South Dakota.
Nebraska
Not listed Not on Nebraska threatened and endangered species (163 Neb. Admin. Code ch. 4, § 004). NatureServe: SNR, not yet ranked in Nebraska. 163 NAC 4-004
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 peopleToxic (severe, per USDA)

USDA PLANTS rates its toxicity as “severe.” (USDA's rating covers people and livestock and doesn't say which parts.) NC State Extension has no page for it. USDA PLANTS

For petsToxic to horses (not dogs or cats)

ASPCA's entry “Loco Weed (Oxytropis spp.)” (Oxytropis spp), which covers the whole genus, lists it as toxic to horses, but non-toxic to dogs and cats. Signs include: Incoordination, depression, inability to eat and drink, fetal death and birth defects Credit: Image Courtesy of Gary Coffman, PBase.com Gallery… 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 lambert's locoweed in 15 states.

recorded by USDA PLANTS on our state lists not recorded

See the full list of states

Arizona, Colorado, Iowa, Kansas, Minnesota, Missouri, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Utah, Wyoming.

Colorado counties with USDA records: Adams, Alamosa, Arapahoe, Baca, Boulder, Clear Creek, Conejos, Custer, Denver, Dolores, Douglas, El Paso, Elbert, Fremont, Garfield, Gilpin, Grand, Gunnison, Huerfano, Jackson, Jefferson, Kiowa, Kit Carson, Lake, Larimer, Las Animas, Logan, Mesa, Mineral, Park, Phillips, Pueblo, Rio Blanco, Rio Grande, Routt, Saguache, Sedgwick, Teller, Weld, Yuma.

North Dakota counties with USDA records: Adams, Barnes, Benson, Billings, Bottineau, Bowman, Burke, Burleigh, Cass, Dickey, Divide, Dunn, Emmons, Golden Valley, Grand Forks, Grant, Hettinger, Kidder, LaMoure, McHenry, McIntosh, McKenzie, McLean, Mercer, Morton, Mountrail, Oliver, Pierce, Ramsey, Ransom, Renville, Richland, Sargent, Sioux, Slope, Stark, Stutsman, Ward, Wells, Williams.

South Dakota counties with USDA records: Aurora, Bennett, Bon Homme, Brown, Brule, Butte, Charles Mix, Clay, Corson, Custer, Davison, Dewey, Edmunds, Fall River, Faulk, Grant, Gregory, Haakon, Hanson, Harding, Hughes, Hutchinson, Hyde, Jackson, Jerauld, Lawrence, Lincoln, Lyman, McCook, Meade, Mellette, Minnehaha, Pennington, Stanley, Todd, Tripp, Turner, Union, Walworth, Yankton, Ziebach.

Growing conditions

USDA PLANTS gives Lambert's locoweed a high shade tolerance, medium drought tolerance and low moisture use. It is rated for soil pH 6.4 to 9.0 and winter lows down to -38 °F.

Shade tolerance
High
Drought tolerance
Medium
Moisture use
Low
Soil textures it is adapted to
coarse, medium
Soil pH range
6.4 to 9.0
Minimum temperature tolerated
-38 °F
Frost-free days needed (minimum)
90
Annual precipitation range
16 to 24 inches
Minimum root depth
10 inches
Salinity tolerance
Low
Fertility requirement
Low
Growth rate
Moderate
Lifespan
Moderate
Active growth period
Spring and Summer
Fruit or seed
Brown · Spring to Summer
Can be propagated by
seed
Commercial availability
No Known Source

From the USDA PLANTS characteristics data for OXLA3. USDA ratings are general guidance for the species, not a guarantee for your garden.

Names, range and relatives

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

County records: USDA PLANTS lists it in 413 counties across 15 states; the most are in Nebraska (57), Kansas (54), South Dakota (41).

Other Oxytropis on Bloomipedia (1): White point-vetch.

More from the Fabaceae family (114 on Bloomipedia; most observed first): Lupines, White clover, Red clover, Eastern redbud, Purple crownvetch, Bird's-foot trefoil, Partridge pea, White sweetclover.

More Colorado flowers

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Wild licorice (Glycyrrhiza lepidota)

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Sources