Bishop's-Weed, Greater Ammi

Ammi majus

Apiaceae


Description

Bishop's-weed is a showy, coolseason annual up to 3 feet tall. The oblong leaves may be up to 8 inches long and 5.5 inches wide.

The many white flowers are arrayed in an umbrella shape up to 3 inches across located at branch tips. Each flower gives rise to a small, oblong, rough fruit.


Habitat

This plant was introduced from the Mediterranean region and has been widely disseminated in the Western Hemisphere. It is found in east and south Texas, usually along roadsides, as it has apparently been included in some wildflower seed mixes. In the past 15 years, bishop's weed has become more widespread, and is now established in some roadside pastures. It is likely to spread further in coming years, posing a greater threat to livestock.


Toxic Agent

Bishop's-weed contains a furocoumarin in all parts of the plant, but it is especially concentrated in the seed. The compound is photoactive, causing primary photosensitization in cattle, sheep and birds. All animals consuming the seed should be considered at risk.


Signs of Livestock Ingestion

Signs in affected animals: increased body temperature; Photophobia (the animals shy away from light); Edema of the muzzle, ears, udder, scrotum and vulva; Sunburn of light-colored skin; Inflammation of skin.

Thin-skinned areas and those having thin or no hair are often those most affected. Inflammation is followed by swelling, blisters, fluid seepage and sometimes sloughing of the skin.

In dark animals, the skin is not blistered or sloughed, but may become painful and thickened, with crusted hair.


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