Sphenosciadium capitellatum, also commonly referred to as ‘Ranger Button’ is a stout perennial herb growing from a tuberous root and producing an erect stem often exceeding a 3 feet tall and sometimes approaching 6 feet. Like many members of the carrot family, small white flowers grow from a compound umbel at the end of the rootstalk. However, unlike most other members, the umbellets of Sphenosciadium capitellatum are nearly spherical. The stem and leaves are usually green but sometimes nearly white in color, smooth below but with rough hairs on the inflorescence. The leaves are divided into several segments which bear widely-spaced leaflets. The leaflets may also be intricately divided into small segments. It is native to western North America from Idaho through Nevada and California into Baja California. It grows in moist habitat types, such as creeksides, streams and meadows at elevations of 3,000 to over 10,000ft.
All parts of the plant should be considered toxic and have been shown to cause photosensitization and pulmary edema in cattle, sheep, and humans as a result of ingestion. 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 large amounts of the plant their body is unable to fully metabolize it. This allows photoreactive compounds to be deposited throughout the tissues of the body. When exposed to the UV radiation of sunlight, the now photoreactive tissue reacts by becoming energized. This reaction yields free radicals that literally “burn” the tissue. The affected tissue will become wrinkled, blistered, or split apart creating open wounds, and the surface may eventually slough away. It may take weeks to recover and obvious scarring may remain forever. Additionally the tissue damage may be so severe that it completely debilitates the animal or allows necrosis and secondary infections that kill the animal. Even more damaging than how it affects the skin is how it affects the eyes, in that animals may experience cloudy corneas, conjunctivokeratitis and permanent scaring of the eyes that will leave the animal permanently blind.
The exact amount needed to create intoxication in animals has not been fully documented. In experiments with cattle 10 to 16 g/kg body weight produced severe respiratory distress with 2 to 4 hours and death from 4 hours to 2 ½ days after ingestion. Additional symptoms included a distended neck, weakness, slight salivation, and apparent abdominal pain. Post mortem, the animals had a bloody discharge seeping from the nose and mouth, obvious bloating, and marked anal protrusion. In horses dosed with Sphenosciadium, the animals become photophobic, developed severe discharge of tears from the eyes when exposed to light, blindness due to cloudiness of the cornea. Additionally they developed swollen red lesions on the non pigmented areas of the nose. Once the dosing was stopped, the skin lesions healed within two weeks but the eyes remained cloudy for over 2 months.
There is no specific antidote for ingestion of Sphenosciadium capitellatum, as such treatment is going to be palliative. In the event the animal is witnessed eating the plant or identifiable plant matter is found in the mouth remove any existing plant matter from the mouth and flush the mouth thoroughly with water. In dogs and cats, if it is believed that the animal may have consumed a massive amount of parsley vomiting may be induced by giving a teaspoon or less (size dependent) of 3% hydrogen peroxide orally; a cathartic to stimulate elimination may prove beneficial. In the overwhelming majority of cases where only a small amount was ingested the animal will make a full recovery without the aid of treatment.
In cases of a massive ingestion gastric lavage and the administration of activated medical charcoal may be very useful in ridding the body of the toxin. If the animal begins to suffer photosensitivity it should be kept away from sunlight and fully shaded. Grazing animals suffering from photosensitivity should be housed in a cool dark place during the day and only allowed to graze during darkness. The severe stress of photosensitization and extensive skin necrosis can be highly debilitating and increase mortality. Corticosteroids, given parenterally in the early stages, may be helpful. Secondary skin infections and suppurations should be treated with basic wound management techniques, and fly strike prevented. The skin lesions heal remarkably well, even after extensive necrosis. Animals suffering pulmary edema may require oxygen therapy, morphine, or diurietics. Severely affected animals may have so little pulmonary reserve that any driving or handling must be done with extreme caution to prevent immediate death. The prognosis will depend upon the severity of the intoxication. For animals suffering advanced clinical signs such as pulmary edema the prognosis is guarded to poor, whereas those not yet severely affected will likely to recover. Those that do recover will do so in a matter of days to weeks; although visible scarring and/or damage to the eyes may remain for the life of the animal.