Poisonous Plants of the Southern United States

johnsongrass.jpg (52859 bytes)johnsongrass
Sorghum halepense

Coarse grass up to 2 m tall with stout rhizomes, appearing in dense clumps or nearly solid stands. Leaves on vigorous plants up to.6 m long and 3 cm wide, pilose on upper leaf surface near the base. Panicle often appearing purplish, up to .6 m long and .2 m broad. Spikelets 4 to 6 min long enclosing a 2 mm long grain. Found throughout the south; most abundant in fields, waste places, fence rows and on ditch banks. Particularly abundant in rich delta la such as in Mississippi. Once widely cultivated as a hay and pasture crop.


Under conditions of drought, trampling, frost, or second growth, the plants may contain cyanide. In addition, if heavily fertilized with nitrogen, there is a possibility of nitrate poisoning if the plants are drought stricken.

All animals can be poisoned by cyanide, however, ruminants are more susceptible. Nitrate poisoning occurs most commonly in ruminants, although cases of nitrite poisoning have occurred in monogastric animals.


Cyanide poisoning is very acute and affected animals exhibit difficult breathing, anxious expression, staggering and usually become recumbent, have convulsions and die. Animals may show signs within 15-30 minutes after consuming plants containing cyanide and may die very quickly. The blood is usually bright red.

In nitrate poisoning, the symptoms are similar except the blood is characteristically chocolate-brown.


For cyanide poisoning sodium thiosulfate and sodium nitrite intravenously are used as an antidote.

For nitrate poisoning, two percent methylene blue is specific.


Plants containing cyanide can be ensiled or cut for hay. After drying, most of the cyanide is eliminated. Be careful when allowing cattle to graze Johnson grass, sorghums, etc., that have been frosted, wilted, trampled, or drought stricken.

Hay made from the plants may contain nitrate, however, and should therefore be analyzed if suspect.


yellowjessamine.jpg (55411 bytes)yellow jessamine
Gelsemium sempervirens

Climbing or trailing, somewhat woody, perennial vine. Leaves opposite, evergreen, lanceolate, 3 to 7 cm long, 1 to 2.5 cm wide, tips acute to acuminate, margins entire. Flowers showy, yellow, fragrant, to 3 cm long, 1 to 3 in axils of leaves, blooming in early spring. Fruit a many seeded, compressed capsule. Found from bluffs to swamps, throughout the south; most abundant along fence rows and in open woods. Often confused in the vegetative stage with Lonicera japonica which has broader, deciduous leaves.


The toxic principles are the alkaloids gelsemine, gelseminine and gelsemoidine. These toxins are related to strychnine.

Livestock are affected, usually in the winter and spring months, from eating any parts of the plant. Humans have been known to be poisoned from sucking the nectar from the flowers or from eating honey made from these flowers. Bee deaths have been blamed on the nectar.


Animals are usually found staggering and incoordinated, with dilated eyes and convulsive movements. Often the animals are found down in comatose condition. Death usually occurs soon after the animal becomes comatose.


There is no specific treatment.

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