Heracleum maximum
Apiaceae
Cow Parsnip; American Cow Parsnip; American Cow-parsnip; Pushki; Alaskan Cow Parsnip; Indian Celery; Indian Rhubarb; Satan Celery; Poison Turnip; Cow Parsley; Hogweed; Heracleum lanatum; Heracleum maximum
Furanocoumarins and psoralen-type phototoxic compounds, including xanthotoxin, bergapten, psoralen, angelicin, pimpinellin, isopimpinellin, isoimperatorin, isobergapten, sphondin, and related Heracleum furanocoumarins; nitrates may also be a concern depending on growing conditions. Sap exposure followed by sunlight is the major practical risk.
Photosensitization, phytophotodermatitis, sunburn-like skin injury, redness, itching, swelling, blistering, ulcerative and exudative dermatitis, wrinkling or sloughing of damaged skin, painful lesions on lightly haired or unpigmented areas, especially the ears, muzzle, lips, nose, eyelids, udder, vulva, and lower limbs; photophobia, cloudy cornea, conjunctivitis, conjunctivokeratitis, eye pain, tearing, corneal injury, and possible blindness. Ingestion may also cause gastrointestinal upset, drooling, vomiting, diarrhea, abdominal discomfort, depression, and, where nitrate accumulation is involved, weakness, labored breathing, dark mucous membranes, tremors, collapse, or sudden death in grazing animals.
Cow Parsnip, Heracleum maximum, also commonly known as American Cow Parsnip, Pushki, Alaskan Cow Parsnip, Indian Celery, Indian Rhubarb, Satan Celery, Poison Turnip, Cow Parsley, and Hogweed, is a tall native member of the carrot family, Apiaceae. It is the only member of the genus Heracleum native to North America and is found in moist meadows, stream banks, riparian areas, marsh edges, damp open woods, roadsides, pastures, and disturbed wet areas.
Its exact scientific name has varied over time. Older and regional sources may refer to it as Heracleum lanatum, H. maximum, H. linatum, H. sphondylium subsp. montanum, or H. sphondylium var. lanatum. For this entry, the current clean name is Heracleum maximum, with Heracleum lanatum preserved as an important synonym for older references, plant guides, herbals, weed manuals, and toxic-plant databases.
Reaching heights of more than six feet, Cow Parsnip is a large, coarse, impressive herbaceous plant. The genus name Heracleum, from “Hercules,” refers to the large size of all parts of these plants. Cow Parsnip has the characteristic flower umbels of the carrot family, often several inches across, flat-topped to rounded, and composed of many small white flowers. Sometimes the outer flowers of the umbel are much larger than the inner flowers, giving the inflorescence a lacy, uneven appearance.
The leaves are very large, sometimes more than 15 inches across, divided into broad lobes, and the stems are stout, succulent, hairy, and hollow or partially hollow. The plant is distributed throughout much of the continental United States except portions of the Gulf Coast and neighboring states. It occurs from sea level to high elevations and is especially well known in Alaska and the Pacific Northwest. It is listed as Endangered in Kentucky and Special Concern in Tennessee. In Canada, it is found in most provinces and territories. In portions of its range, it may behave as a weedy or invasive plant in disturbed moist sites.
Cow Parsnip is often confused with Giant Hogweed, Heracleum mantegazzianum, and with several other large white-flowered Apiaceae plants. That confusion matters. Giant Hogweed is generally considered more severe and more aggressively regulated in many areas, but Cow Parsnip itself can still cause significant skin and eye injury. Some pet-poison databases cross-list Cow Parsnip with Giant Hogweed, but the cleaner botanical treatment is to keep Cow Parsnip as Heracleum maximum and Giant Hogweed as a separate Heracleum species.
The plant is toxic and poses a risk to both companion and agricultural animals. The primary toxins are furanocoumarins, including psoralen-type compounds such as xanthotoxin and bergapten. These compounds are phototoxic. They become especially damaging when plant sap contacts skin or eyes and is then exposed to ultraviolet radiation from sunlight. Current plant and toxicology references consistently identify Cow Parsnip sap as capable of causing phytophotodermatitis, blistering, dermatitis, and photosensitivity.
All parts of the plant should be treated with caution, but the sap is the most important practical hazard. Sap may be released when the plant is chewed, trampled, grazed, cut, broken, mowed, pulled, or crushed. An animal does not necessarily have to eat a large amount of the plant to be injured. Contact with sap on the muzzle, lips, nose, ears, eyelids, udder, vulva, lightly haired skin, or unpigmented skin, followed by sunlight exposure, can be enough to cause a painful phototoxic burn.
Photosensitization is a clinical condition in which areas exposed to light and lacking significant protective hair, wool, or pigmentation become hyperreactive to sunlight due to the presence of photodynamic agents. When animals ingest or contact the plant, photoreactive compounds may be absorbed or deposited in tissues. When exposed to ultraviolet radiation, the photoreactive tissue becomes energized, producing free radicals that literally “burn” the tissue.
The affected tissue may become red, swollen, painful, wrinkled, blistered, split, ulcerated, or exudative. Open wounds may form, and the surface may eventually slough away. It may take weeks to recover, and obvious scarring or pigment change may remain for a long time. In severe cases, tissue damage may be debilitating or may allow secondary infections, necrosis, fly strike, or other complications that endanger the animal.
Even more damaging than the effect on the skin is the potential effect on the eyes. Animals may experience photophobia, tearing, conjunctivitis, cloudy corneas, conjunctivokeratitis, corneal injury, and permanent scarring of the eyes that may leave the animal partially or completely blind. This is why facial, muzzle, eyelid, or eye exposure should be treated more seriously than a minor skin exposure on a well-haired area.
In companion animals, the most likely exposures involve dogs running through wet vegetation, chewing stems, mouthing leaves, contacting sap on the muzzle, or walking through crushed plants along trails, ditches, creek banks, or overgrown field edges. Cats are less likely to encounter large amounts outdoors but could still be exposed if they brush against damaged plants or chew fresh plant material. In both dogs and cats, skin, mouth, and eye exposure followed by sunlight is the main concern.
In grazing animals, including cattle, sheep, goats, horses, and other livestock, Cow Parsnip and related phototoxic Apiaceae plants may cause photosensitization when eaten or when sap contacts exposed skin. Risk increases in animals with white or lightly pigmented skin, thin hair cover, recently clipped coats, exposed muzzles, ears, udders, or vulvar tissue, and in animals grazing open sunny areas where damaged plants are present.
Nitrates may also be a concern depending on growing conditions, especially in rich soils, fertilized areas, disturbed ground, drought-stressed growth, regrowth, or other conditions that favor nitrate accumulation. For this plant, however, the headline hazard remains furanocoumarin-associated photosensitization and sap-related photodermatitis.
For practical prevention, avoid allowing pets or livestock to chew, trample, or graze Cow Parsnip, especially in sunny conditions. Do not mow, cut, pull, or handle the plant casually in areas where pets or animals will immediately pass through the fresh sap. If the plant is cut or crushed, animals should be kept away until the plant material is removed and the area no longer contains fresh sap exposure.
Immediate Response to Cow Parsnip Exposure
- Remove the Source: Prevent further exposure by moving the animal away from Cow Parsnip, crushed stems, fresh sap, leaves, flowers, seeds, roots, clippings, mowed material, or contaminated pasture.
- Limit Sunlight Immediately: Because the major toxin effect is activated by ultraviolet light, move the animal into shade, indoors, a barn, a stall, or another low-light area as quickly as possible.
- Remove Plant Material from the Mouth: If the animal was chewing the plant and it is safe to do so, remove visible plant material from the mouth and flush the mouth thoroughly with water.
- Wash Sap-Exposed Skin: If sap may have contacted the skin, muzzle, lips, nose, ears, eyelids, paws, udder, vulva, or other exposed tissue, wash the area thoroughly with water and mild soap if appropriate. Wear gloves when handling the animal or plant material to avoid human skin exposure.
- Protect the Eyes: If sap may have contacted the eyes, eyelids, or face, veterinary guidance is strongly recommended. Eye exposure can be serious and may lead to corneal injury or blindness.
- Watch for Delayed Burns: Redness, swelling, blistering, itching, ulceration, skin sloughing, photophobia, cloudy cornea, tearing, or eye pain may develop after sunlight exposure and should be treated seriously.
- Contact Veterinary Help: Consult a veterinarian, emergency veterinary clinic, livestock veterinarian, Pet Poison Helpline, or another animal poison-control professional if ingestion occurred, if sap exposure is significant, if eyes or face are involved, if blistering develops, or if the exposed animal is a dog, cat, horse, cow, sheep, goat, young animal, elderly animal, pregnant animal, or medically fragile animal.
Ingestion and Decontamination
- No Specific Antidote: There is no specific antidote for Cow Parsnip exposure. Treatment is palliative, symptomatic, and focused on decontamination, sunlight avoidance, skin and eye protection, and supportive care.
- Getting Plant Material Out Matters: If a dog has recently swallowed Cow Parsnip plant material, removing remaining plant material from the stomach may reduce continued exposure to furanocoumarins and other irritant compounds.
- Inducing Vomiting in Dogs Only: In dogs, if ingestion was recent and the dog is alert, breathing normally, able to swallow, and not showing weakness, collapse, repeated vomiting, severe depression, respiratory distress, neurologic signs, severe mouth irritation, or signs of aspiration risk, a veterinarian or animal poison-control professional may recommend inducing vomiting with fresh 3% hydrogen peroxide.
- Cat Warning: Hydrogen peroxide should not be used to induce vomiting in cats unless a veterinarian specifically directs it. Cats are more prone to irritation and complications from hydrogen peroxide, and home vomiting attempts may create more risk than benefit.
- Do Not Induce Vomiting in an Unstable Animal: Vomiting should not be attempted in any animal that is weak, collapsed, sedated, having trouble breathing, unable to swallow normally, already vomiting repeatedly, showing neurologic signs, or otherwise unstable.
- Activated Charcoal: Activated charcoal may be useful after significant ingestion, but it should be administered under veterinary or poison-control direction, especially if the animal is vomiting, weak, or at risk of aspiration.
- Gastric Lavage or Cathartic: In large or high-risk ingestion cases, a veterinarian may consider gastric lavage or a cathartic to stimulate elimination depending on timing, species, amount, and clinical signs.
Photosensitization and Skin Treatment
- Shade and Darkness: While photosensitivity continues, the animal should be kept away from sunlight and fully shaded. This is not optional; ultraviolet exposure is what activates much of the tissue injury.
- Grazing Animals: For cattle, sheep, goats, horses, and other grazing animals, affected animals should be housed in a cool, dark place during the day and only allowed outside or to graze during darkness until photosensitivity has resolved.
- Skin Lesions: Blistering, ulceration, oozing, sloughing, and painful skin lesions should be managed with veterinary wound care.
- Corticosteroids: Corticosteroids given parenterally in the early stages may be helpful under veterinary direction to reduce inflammation and tissue damage.
- Secondary Infection: Secondary skin infections and suppurations should be treated with basic wound-management techniques and appropriate veterinary care.
- Fly Strike Prevention: In livestock and outdoor animals, fly strike must be prevented when open wounds, oozing lesions, or necrotic tissue are present.
Eye and Respiratory Concerns
- Eye Exposure: Photophobia, cloudy cornea, tearing, squinting, conjunctivitis, conjunctivokeratitis, or suspected eye contact should prompt veterinary evaluation because permanent eye damage is possible.
- Facial Swelling: Swelling of the muzzle, lips, eyelids, or face should be monitored carefully, especially if the animal is having trouble eating, drinking, seeing, or breathing normally.
- Severe Cases: Extensive skin necrosis, dehydration from open lesions, secondary infection, severe ocular injury, or systemic weakness may require intensive veterinary management.
Pasture, Trail, and Yard Management
- Remove Access: Keep animals away from Cow Parsnip growing along streams, wetlands, trails, pasture edges, ditches, roadsides, and damp meadows.
- Handle Carefully: Wear gloves, long sleeves, eye protection, and protective clothing when cutting or removing Cow Parsnip, and avoid working in full sun when sap exposure is likely.
- Do Not Leave Fresh Clippings: Do not leave fresh cut stems, leaves, or sap-covered debris where dogs, livestock, or other animals can contact or ingest them.
- Monitor White or Light Areas: Animals with white muzzles, white ears, pink skin, clipped coats, or lightly pigmented areas should be monitored especially carefully after exposure.
Prognosis and Recovery
- Prompt Decontamination: Prognosis is generally good when exposure is recognized quickly, sap is washed off, sunlight is avoided, and skin or eye lesions are treated promptly.
- Skin Recovery: Skin lesions may heal well, even after extensive necrosis, but recovery can take days to weeks and scarring or pigment change may remain.
- Eye Damage: Prognosis is more guarded when the eyes are involved because corneal scarring or permanent vision damage may occur.
- Severe Photosensitization: Extensive skin necrosis, secondary infection, fly strike, severe stress, or inability to keep the animal out of sunlight can worsen prognosis and increase mortality risk.
- Prevention: Prevent further ingestion or contact, remove animals from Cow Parsnip areas, control the plant where animals graze or travel, and consult a veterinarian promptly when significant exposure occurs.