Black greasewood
Sarcobatus vermiculatus
Oxalate poisoning can be fatal to livestockColorado · 154 profiles · 462 photographs
Know what is growing.
An illustrated reference to garden weeds and wild plants found in Colorado. Compare what plants look like and read sourced information about their effects on people, animals and local habitats. Open a plant card to see its photographs, descriptions and source links.
Biggest concerns · Coverage: all 82 state-list entries · Exposure and safety guide · Learn to use this guide
Native volunteers
29 plants
Broom snakeweed
Gutierrezia sarothrae
Livestock poisoning and abortion risk when heavily eaten
Buffalobur
Solanum rostratum
Sharp spines; toxic to livestock
Canada goldenrod
Solidago canadensis
Spreads by roots and seed
Catchweed bedstraw
Galium aparine
Hooked hairs and burrs cling to fur and clothing
Common blue violet
Viola sororia
A native volunteer; identify the species before removing
Common ragweed
Ambrosia artemisiifolia
Pollen allergy; skin irritation
Common sunflower
Helianthus annuus
Listed non-toxic to dogs & cats
Curlycup gumweed
Grindelia squarrosa
Sticky resin and conditional selenium concern
Foxtail barley
Hordeum jubatum
Barbed seed awns injure animals
Giant ragweed
Ambrosia trifida
Allergenic pollen and strong competition in disturbed ground
Golden banner
Thermopsis divaricarpa
May poison livestock
Hemp dogbane
Apocynum cannabinum
Cardiac-glycoside poisoning hazard for people and animals
Horseweed
Erigeron canadensis
Fast windborne spread; some populations resist herbicides
Low larkspur
Delphinium nuttallianum
Serious livestock and pet poisoning hazard
Meadow death camas
Toxicoscordion venenosum
Potentially fatal ingestion; onion-like bulbs
Netseed lambsquarters
Chenopodium berlandieri
A fast-growing volunteer; pet toxicity remains unresolved
Prairie sage
Artemisia ludoviciana
Spreading roots; pet evidence gap
Showy milkweed
Asclepias speciosa
Toxic if eaten
Silverleaf nightshade
Solanum elaeagnifolium
Toxic leaves and berries; persistent spreading roots
Snow-on-the-mountain
Euphorbia marginata
Latex can damage skin and eyes; toxic if eaten
Spotted spurge
Euphorbia maculata
Milky sap can injure skin and eyes; keep pets from chewing
Stinging nettle
Urtica dioica
Stinging hairs; this profile covers a taxonomic complex
Tall larkspur
Delphinium barbeyi
Serious livestock and pet poisoning hazard
Western poison ivy
Toxicodendron rydbergii
Skin-rash oil can travel on pet fur
Western ragweed
Ambrosia psilostachya
A persistent perennial ragweed; allergy detail still under review
Western water hemlock
Cicuta douglasii
Potentially fatal poisoning; wetland look-alike danger
Western whorled milkweed
Asclepias subverticillata
High livestock toxicity
White locoweed
Oxytropis sericea
Toxic to livestockXeriscape spreaders
14 plants
Big sagebrush
Artemisia tridentata
Valuable native habitat; subspecies and pet evidence need care
Blanketflower
Gaillardia aristata
Contact dermatitis possible
Catmint
Nepeta × faassenii
Spreading clumps; pet evidence gap
Common yarrow
Achillea millefolium
Toxic to pets · Skin irritation
Fernleaf yarrow
Achillea filipendulina
Spreads; pet toxicity unresolved
Fringed sage
Artemisia frigida
Spreading growth; pet evidence gap
Lamb’s-ear
Stachys byzantina
Can spread; pet evidence gap
Lewis blue flax
Linum lewisii
Ingestion and contact concerns
Plains pricklypear
Opuntia polyacantha
Sharp spines around paws, mouths and eyes
Red valerian
Centranthus ruber
Self-seeds beyond garden beds
Rubber rabbitbrush
Ericameria nauseosa
A native low-water shrub that can spread readily
Russian sage
Salvia yangii
Spreads by suckers; pet evidence unresolved
Snow-in-summer
Cerastium tomentosum
Spreading habit · Safety gap
Soapweed yucca
Yucca glauca
Sharp leaves · Toxic to petsInvasive & common weeds
111 plants
Absinth wormwood
Artemisia absinthium
Ingestion toxicity and skin irritation
African rue
Peganum harmala
Highly poisonous if eaten; deep-rooted invader
Annual sowthistle
Sonchus oleraceus
Windborne seed and crop-pest hosting
Bittersweet nightshade
Solanum dulcamara
Poisonous berries and foliage
Black henbane
Hyoscyamus niger
Highly poisonous; keep animals away
Bohemian knotweed
Reynoutria × bohemica
Hybrid regrows from small fragments
Bouncingbet
Saponaria officinalis
Saponins can cause digestive poisoning
Bulbous bluegrass
Poa bulbosa
Early-season grass spreads by bulbils
Bull thistle
Cirsium vulgare
Sharp spines; competes with vegetation
Camelthorn
Alhagi maurorum
Thorns and deep spreading roots
Canada thistle
Cirsium arvense
Sharp spines; competes with vegetation
Cheatgrass / downy brome
Bromus tectorum
Grass awns · Fire hazard
Chicory
Cichorium intybus
Roadside and pasture spread
Chinese clematis
Clematis orientalis
Smothers vegetation; irritating plant compounds
Common burdock
Arctium minus
Burs and fine bristles injure animals
Common chickweed
Stellaria media
A cool-season weed that can seed while still small
Common cocklebur
Xanthium strumarium
Burs catch in fur; seedlings and seeds are hazardous
Common crupina
Crupina vulgaris
Dense stands reduce forage
Common dandelion
Taraxacum officinale
Persistent lawn volunteer; sap can irritate skin
Common lambsquarters
Chenopodium album
Prolific garden weed; ingestion caution
Common mallow
Malva neglecta
Tough taproot and persistent lawn seedbank
Common mullein
Verbascum thapsus
Dense rosettes and persistent volunteers
Common purslane
Portulaca oleracea
Pet ingestion hazard despite human food uses
Common St. Johnswort
Hypericum perforatum
Photosensitivity and animal exposure concerns
Common tansy
Tanacetum vulgare
Toxic ingestion; contact dermatitis
Common teasel
Dipsacus fullonum
Prickly heads; prolific seed spread
Creeping woodsorrel
Oxalis corniculata
Oxalate-containing plant; keep pets from grazing
Crownvetch
Securigera varia
Toxic to horses; spreading roots can smother vegetation
Curly dock
Rumex crispus
Soluble oxalates; persistent roots and seeds
Cutleaf teasel
Dipsacus laciniatus
Prickly stands can displace native vegetation
Cypress spurge
Euphorbia cyparissias
Sap can injure skin and eyes
Dalmatian toadflax
Linaria dalmatica
Spreads from roots; livestock concern
Dame’s rocket
Hesperis matronalis
Escapes gardens and spreads
Diffuse knapweed
Centaurea diffusa
Skin irritation; tumbling seed spread
Dyer’s woad
Isatis tinctoria
Persistent seed spread
Elongated mustard
Brassica elongata
Early detection priority in dry disturbed land
Eurasian watermilfoil
Myriophyllum spicatum
Fragments spread dense aquatic growth
Field bindweed
Convolvulus arvensis
Smothers plants; livestock concern
Flowering rush
Butomus umbellatus
Small fragments spread aquatic colonies
Giant knotweed
Reynoutria sachalinensis
Very persistent riparian colonies
Giant reed
Arundo donax
Dense stands displace riparian plants
Giant salvinia
Salvinia molesta
Floating mats harm aquatic habitat
Green foxtail
Setaria viridis
Identify the grass behind the name “foxtail”
Hairy willow-herb
Epilobium hirsutum
Spreads through wetland vegetation
Halogeton
Halogeton glomeratus
Severe oxalate poisoning in livestock
Henbit
Lamium amplexicaule
An early-flowering weed with useful nectar
Hoary cress
Lepidium draba
Spreading roots; possible livestock poisoning
Houndstongue
Cynoglossum officinale
Toxic to livestock
Spotted × diffuse knapweed hybrid
Centaurea × psammogena
Hybrid identification needs expert review
Yellow × Dalmatian toadflax hybrid
Linaria vulgaris × Linaria dalmatica
Variable hybrid; persistent spreading roots
Hydrilla
Hydrilla verticillata
Dense aquatic growth; wildlife disease association
Japanese knotweed
Reynoutria japonica
Root and stem fragments regrow
Jimsonweed
Datura stramonium
Serious poisoning risk to people and animals
Johnsongrass
Sorghum halepense
Livestock cyanide risk; added fire fuel
Jointed goatgrass
Aegilops cylindrica
Wheat-field and rangeland seed spread
Kochia
Bassia scoparia
Tumbling seed spread; livestock poisoning risk
Large crabgrass
Digitaria sanguinalis
Fast seed production in thin lawns
Leafy spurge
Euphorbia esula
Irritating sap; eye injury risk
Mayweed chamomile
Anthemis cotula
Crop weed with unpleasant-smelling foliage
Meadow knapweed
Centaurea × moncktonii
Outcompetes pasture and meadow plants
Mediterranean sage
Salvia aethiopis
Tumbles and spreads seed through rangeland
Medusahead
Taeniatherum caput-medusae
Barbed awns; persistent fire-promoting thatch
Moth mullein
Verbascum blattaria
Long-lived seeds sustain infestations
Musk thistle
Carduus nutans
Sharp spines; competes with vegetation
Myrtle spurge
Euphorbia myrsinites
Poisonous · Eye & skin injury
Narrow-leaved Dalmatian toadflax
Linaria genistifolia
Listed taxon with difficult identification
Orange hawkweed
Pilosella aurantiaca
Runners crowd lawns and mountain meadows
Oxeye daisy
Leucanthemum vulgare
Toxic to dogs and cats; dermatitis
Parrotfeather
Myriophyllum aquaticum
Aquatic mats obstruct waterways
Perennial pepperweed
Lepidium latifolium
Deep roots form persistent wetland colonies
Perennial sowthistle
Sonchus arvensis
Persistent underground spread
Plumeless thistle
Carduus acanthoides
Sharp spines; pasture competition
Poison hemlock
Conium maculatum
Poisonous to people & animals
Prickly lettuce
Lactuca serriola
Prickly leaves and prolific windborne seed
Prickly sowthistle
Sonchus asper
Spiny leaves and rapid seed production
Prostrate knotweed
Polygonum aviculare
A mat-forming weed of compacted ground
Puncturevine / goathead
Tribulus terrestris
Sharp burs · Animal injury
Purple loosestrife
Lythrum salicaria
Crowds out wetland vegetation
Quackgrass
Elymus repens
Rhizome fragments regrow in lawns and gardens
Redroot pigweed
Amaranthus retroflexus
Crop competition; nitrate and oxalate livestock risk
Redstem filaree
Erodium cicutarium
Seeds spread through lawns and pasture
Rush skeletonweed
Chondrilla juncea
Deep roots and fragments sustain spread
Russian knapweed
Rhaponticum repens
Toxic to horses
Russian olive
Elaeagnus angustifolia
Thorns; riparian habitat concern
Russian thistle
Salsola tragus
Prickly tumbleweeds; livestock and fire hazards
Scentless chamomile
Tripleurospermum inodorum
Prolific seeds; reported livestock irritation
Scotch thistle
Onopordum acanthium
Sharp spines; competes with vegetation
Shepherd’s purse
Capsella bursa-pastoris
An early-seeding lawn and garden weed
Siberian elm
Ulmus pumila
Numerous seedlings; weak branches
Spotted knapweed
Centaurea stoebe
Competes with native vegetation
Squarrose knapweed
Centaurea virgata
Spiny seedheads; loss of rangeland forage
Sulfur cinquefoil
Potentilla recta
Persistent pasture and roadside weed
Tall buttercup
Ranunculus acris
Fresh plant irritation and animal poisoning hazard
Tamarisk
Tamarix ramosissima
Alters riparian vegetation
Tansy ragwort
Jacobaea vulgaris
Poisonous to livestock; harmful alkaloids
Taurian thistle
Onopordum tauricum
Sharp spines; taxon listed as Scotch thistle
Tree of heaven
Ailanthus altissima
Root suckers form persistent thickets
Tumble mustard
Sisymbrium altissimum
Another tumbleweed: brittle plants scatter persistent seed
Velvetleaf
Abutilon theophrasti
Persistent seeds and strong crop competition
Ventenata
Ventenata dubia
Displaces forage and native grassland
White clover
Trifolium repens
A spreading lawn plant with pollinator value
White sweetclover
Melilotus albus
Moldy sweetclover hay can cause dangerous bleeding
Wild caraway
Carum carvi
Spreads by seed; pet safety concern
Wild carrot
Daucus carota
Do not confuse it with highly poisonous hemlocks
Wild parsnip
Pastinaca sativa
Sap plus sunlight can cause severe skin burns
Wild proso millet
Panicum miliaceum
Seed contamination and crop competition
Yellow flag iris
Iris pseudacorus
Ingestion concern; invasive wetland colonies
Yellow nutsedge
Cyperus esculentus
Underground tubers sustain infestations
Yellow starthistle
Centaurea solstitialis
Severe horse poisoning; sharp spines
Yellow sweetclover
Melilotus officinalis
Moldy sweetclover hay can cause dangerous bleeding
Yellow toadflax
Linaria vulgaris
Spreads from roots; livestock concernRead with an AI assistant · Markdown and sources
Markdown: https://denson.github.io/colorado-weed-field-guide/index.md
Text fallback: https://denson.github.io/colorado-weed-field-guide/index.md.txt
Start here: https://denson.github.io/colorado-weed-field-guide/start.md
Source ledger: https://denson.github.io/colorado-weed-field-guide/provenance.json