Rheum rhaponticum L.—Rhubarb
FAMILY: Polygonaceae—the Smartweed Family
This family of plants contains at least 40 genera and more than 800 species, all with jointed stems. Other characters include leaf stipules: united into a tubular sheath called an ocrea; sepals: petaloid; petals: absent; fruit: an achene. The Polygonaceae are not known for their poisonous members but for useful ones such as buckwheat and various ornamental plants. Many elements in the family are weedy.
PHENOLOGY: Rhubarb flowers are borne on tall, hollow stalks in the summer.
DISTRIBUTION: Rheum rhaponticum is a cultivated plant that occasionally escapes from the garden.
PLANT CHARACTERISTICS: Rhubarb can be identified by leaves: large, basal, in clumps; ovate with cordate bases; leaf blades: up to 1.5 m long, margins wavy; petioles: as long as leaf blades, often red, stout; sepals: 6, greenish, whitish, or reddish; stamens: 6 (9); fruit: a 3-winged achene.
POISONOUS PARTS: The flat leaf blade is toxic.
SYMPTOMS: Human consumption of the rhubarb leaf results in gastroenteritis, cramps. nausea, vomiting, weakness, respiratory difficulties, irritation of the mouth and throat, poor clotting of the blood, internal hemorrhaging, coma, and death. In hogs the symptoms are staggering, salivation, convulsions, and death.
POISONOUS PRINCIPLES: Oxalic acid, uncharacterized soluble oxalates, and possibly other toxins are believed responsible for poisonings.
CONFUSED TAXA: Burdocks (see Arctium) are often confused with rhubarb. Burdock leaves are coarse and pubescent; the leaves of rhubarb are glabrous.
SPECIES OF ANIMALS AFFECTED: Rhubarb leaves are known to have caused the death of both humans and livestock.
TREATMENT: (11a)(b) with lime water, chalk, or calcium salts; (7); (26)
OF INTEREST: Several species of Rheum are grown for their bold foliage effects in landscaping. No data are available on the toxicity of these ornamental plants.