Understanding Why Locoweed Is So Dangerous
Locoweed is not a single plant species but a common name for several poisonous plants belonging to the Astragalus and Oxytropis genera. The primary danger comes from a specific toxin called swainsonine, an indolizidine alkaloid that is extremely harmful to mammals. Unlike many other plant toxins, swainsonine is not produced by the plant itself but by a symbiotic fungal endophyte, Undifilum oxytropis, that lives within the plant tissue. This means that the plant is born with the toxin, and all parts—including foliage, flowers, and seeds—are consistently toxic. The concentration of this endophyte-produced swainsonine can vary depending on soil conditions and other environmental factors.
The mechanism of swainsonine poisoning, or "locoism," is based on how it disrupts cellular function. Swainsonine is a potent inhibitor of key enzymes, specifically lysosomal alpha-mannosidase and Golgi alpha-mannosidase II. By inhibiting these enzymes, swainsonine prevents the proper breakdown and processing of complex carbohydrates and glycoproteins within the cells. This leads to a harmful buildup of partially metabolized sugars in the lysosomes, essentially causing cellular constipation and eventual cell death. This cellular dysfunction affects multiple organ systems, with the most profound and irreversible damage occurring in the nervous system.
The Devastating Symptoms of Locoweed Poisoning
When a mammal, including a human, ingests locoweed, the effects are serious and often permanent. The symptoms are a direct result of the neurological and cellular damage caused by swainsonine and can be broken down into several categories:
Neurological Symptoms
- Erratic and Unpredictable Behavior: The most recognizable symptom, especially in livestock, is the peculiar, crazed behavior that gives locoweed its name (from the Spanish "loco" for crazy). Animals may become aggressive, hyperactive, or severely depressed.
- Impaired Coordination (Ataxia): Stumbling, a staggering gait, and an exaggerated high-stepping walk are common signs of nervous system damage.
- Sensory and Vision Problems: Poisoned animals may appear blind or confused, bumping into objects and overreacting to stimuli.
- Physical Manifestations: Head bobbing, fine tremors, and seizures can also occur in severe cases.
Reproductive and Other Systemic Problems
- Reproductive Dysfunction: Locoweed is known to cause decreased fertility, abortion, and the birth of weak or deformed offspring in livestock. The toxin can even be passed to nursing young through milk, causing poisoning.
- Weight Loss and Emaciation: Poor appetite and a general decline in body condition are common symptoms.
- Other Organ Damage: While less obvious, locoweed poisoning can also lead to liver disease, heart failure, and edema.
Can Humans Be Poisoned?
Although poisonings are far more common in grazing animals, the underlying toxicity affects all mammals. A human who ingests locoweed would experience severe symptoms consistent with the neurological and systemic damage caused by swainsonine. The effects could include hallucinations, neurological disturbances, and potentially fatal organ damage. It is crucial to treat any suspected human ingestion as a medical emergency.
The Spectrum of "Locoweed" Toxins
Not all plants referred to as locoweeds contain swainsonine. Some Astragalus species accumulate high levels of selenium from the soil, causing selenium poisoning instead of locoism. In these cases, the toxicity is dependent on the soil composition rather than an endophyte. These plants are often unpalatable and consumed only in desperation. Due to the difficulty in distinguishing toxic species from non-toxic lookalikes and the potential for multiple toxins, it is critically important to assume any suspected locoweed is poisonous.
Primary Locoweed Toxins
- Swainsonine: An indolizidine alkaloid causing locoism, produced by an endophyte fungus.
- Selenium: Accumulates from certain soils, causing distinct selenium poisoning symptoms.
- Nitro Compounds: Some species may contain nitrotoxins, adding to their toxic profile.
A Critical Comparison: Swainsonine vs. Selenium Locoweed
Foraging requires expert knowledge, but when it comes to locoweed, the risks are far too high for experimentation. The table below outlines the dangers of the two primary types of poisonous locoweed and reinforces why avoiding all species is the only safe approach.
| Feature | Swainsonine-Containing Locoweed (Oxytropis & certain Astragalus spp.) | Selenium-Accumulating Locoweed (certain Astragalus spp.) |
|---|---|---|
| Primary Toxin | Swainsonine (indolizidine alkaloid) | Selenium and selenium compounds |
| Source of Toxin | Endophytic fungus within the plant | Mineral absorbed from the soil |
| Effect on Body | Inhibits mannosidase enzymes, causing cellular waste buildup | Causes selenium poisoning, potentially lethal |
| Primary Symptoms | Neurological damage, ataxia, erratic behavior | Blind staggers, alkali disease, hair/hoof loss |
| Palatability | Can be palatable; animals can develop a learned grazing habit | Often unpalatable, eaten only when other forage is scarce |
| Irreversible Damage | Neurological damage is often permanent | Severe cases can be irreversible, less information for humans |
Why Locoweed is Absolutely Not an Edible Wild Plant
The dangers of locoweed are numerous and serious, making it completely unsuitable for human consumption under any circumstances. Key reasons include:
- Extremely High Toxicity: The presence of swainsonine or selenium means even small amounts can be highly poisonous.
- No Reliable Field Identification: Due to the large number of similar-looking Astragalus and Oxytropis species, distinguishing a toxic from a non-toxic plant is practically impossible for the average person.
- Consistency of Toxin: The toxin is present in all parts of the plant and remains potent even after drying.
- Risk of Irreversible Damage: The neurological damage caused by swainsonine is permanent, and there is no cure.
Prevention and What to Do If Ingestion Occurs
The only safe and effective way to deal with locoweed is through avoidance. For those living or hiking in areas where it is present, proper plant identification is critical. Never forage for wild edibles unless you are an expert and can definitively identify the plant. In agricultural settings, managing pastures to prevent livestock access to locoweed is the primary strategy for minimizing economic losses.
If you or someone you know has accidentally ingested any part of a locoweed plant, immediate action is necessary. Do not wait for symptoms to appear. The recommended course of action is to seek immediate emergency medical care. Bring a sample of the plant with you if possible to aid medical professionals in diagnosis. The treatment will focus on supportive care and managing symptoms, as there is no antidote to reverse the effects of swainsonine poisoning. For further information, consult the USDA Agricultural Research Service on poisonous plants.
Conclusion: The Final Verdict on Eating Locoweed
The verdict is clear: you can not, and should never, eat locoweed. The risks associated with this plant far outweigh any potential benefit. From its potent and persistent toxin, swainsonine, to the very real possibility of misidentification with other poisonous species, every aspect of locoweed makes it a threat to mammalian health. Foraging for wild edibles requires caution and expertise, and with a plant as dangerous as locoweed, the most important knowledge to possess is the wisdom to leave it untouched.
USDA Agricultural Research Service - Poisonous Plant Research Laboratory
