Poisonous Plants of the Southern United States

showycrotalaria.jpg (43975 bytes)showy crotalaria
Crotalaria spectabilis

Annual herb, .2 to .5 m tall, densely pubescent. Leaves simple, alternate, linear to lanceolate, upper mostly 3 to 6 cm long, 4 to 10 mm wide; lower leaves spatulate, 2 to 3 cm long, 6 to 15 min wide. Stipules conspicuous, tardily deciduous, fused to stem. Flowers showy, 1.5 to 2.5 cm long, yellow in terminal racemes. Widely distributed from Florida to Texas in coastal plain and piedmont; abundant along roadsides and in fields, waste places; once cultivated as a green manure crop. Plant on the left is Crotalaria striata, also toxic.


All parts of the plant are poisonous, whether green or dried in hay. The seeds are especially poisonous. The toxic principle is the alkaloid monocrotaline. Chickens, horses, cattle and swine are the species usually affected, but sheep, goats, mules and dogs can be affected to a lesser degree. Poisoning occurs from consuming the green plant, hay contaminated with crotalaria, or dried seed in harvested grain.


Death in chickens can occur from as few as 80 seeds. Fatalities may occur within a few days or up to several weeks after ingestion. Symptoms include diarrhea, a pale comb (signifying anemia), ruffled feathers and depression. Quail are also easily poisoned, but turkeys are more tolerant.

Horses develop chronic unthriftiness, become incoordinated, walk aimlessly and may "head press" against various objects. Mucous membranes often exhibit jaundice, related to severe liver damage

In cattle, three syndromes are recognized: acute, chronic and intermediate types. The chronic type is most commonly seen with animals dying several months after consuming the toxic material, usually hay contaminated with crotalaria. Symptoms include bloody diarrhea, icterus, rough hair coat, unthriftiness, edema and weakness.

Swine may exhibit an acute death characterized by sudden gastric hemorrhage and death or a chronic form with symptoms of anemia, ascites, loss of hair and unthriftiness.


There is no specific treatment.


brackenfern.jpg (61279 bytes)bracken fern
Pteridium aquilinum

Coarse perennial fern to 1 m tall. Older fronds leathery, .3 to 1 m long, triangular in outline with three main divisions and many small subdivisions. Rhizomes horizontal, underground, about .5 cm in diameter. Distributed throughout all southern states; most common in old fields, waste places, open woods and roadsides, particularly on relatively dry sites.


The poisonous principle is the enzyme thiaminase which inactivates thiamine (Vitamin B1) in the horse. In ruminants, an aplastic-anemia factor causes depression of the bone marrow. Sheep are less susceptible to the toxic effects than cattle and horses.

All portions of the plant are toxic whether green or dry. Poisoning by the plant is cumulative and symptoms may not appear until several weeks or months later. Clinical cases are most often seen in the spring or late summer or fall, especially after periods of drought when other forage is short or not available. Animals have shown toxicity from consuming hay containing the dried plants.


Horses exhibit incoordination, often standing with their legs spread apart as if bracing themselves. The affected animal arches its back and neck into a crouching stance. Occasionally a fever is present up to 104oF. Prior to death horses may "head press" objects and have spasms with the head and neck drawn backwards.

Cattle may exhibit two types of symptoms. The laryngeal form is seen often in younger animals and is characterized by edema of the throat region resulting in difficult and loud breathing. The enteric form may be preceded by the laryngeal form. Animals thus affected exhibit bloody feces, blood in the urine and excessive bleeding from fly bites. The blood is slow to clot since there is a deficiency of platelets. Death usually occurs within a few days after symptoms appear.

Sheep have shown blindness due to degeneration of the retinal epithelial cells after grazing bracken fern.


Horses often respond to repeated injections of thiamine at a dosage of 100-200 mg. per day for 7-14 days.

In cattle, whole blood transfusions, broad spectrum antibiotics, DL-batyl alcohol and protamine sulfate have all been used with some success. Removal of the animals from areas infested with bracken fern is suggested.

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