Rhubarb-Rheum rhaponticum L.-Poisonous plant

Rhubarb

General poisoning notes:

Rhubarb (Rheum rhaponticum) is a perennial cultivated plant that persists around old farm sites. The plant contains oxalate crystals, which have been reported to cause poisoning when large quantities of raw or cooked leaves are ingested. Anthraquinones (glycosides) have been implicated more recently in the poisoning. The stalks are widely used as preserves and are also eaten raw, without problems. The toxic content is much lower in the stalks. Humans have been poisoned after ingesting the leaves. Human poisoning was a particular problem in World War I, when the leaves were recommended as a food source in Britain. Some animals, including goats and swine, have also been poisoned by ingesting the leaves. Children should be taught to eat only the rhubarb stalks, preferably under supervision (Robb 1919; Cooper and Johnson 1984).

Description

Plants 3-20(-30) dm. Stems striate, often striped or suffused with red or pink, branched distally, hollow. Leaves: ocrea brown, loosely funnelform, 2-4 cm, margins strongly oblique, glabrous or puberulent with flattened, whitish hairs along veins; petioles of basal leaves pinkish green or reddish green, ca. equaling or longer than blade, thick, fleshy, those of cauline leaves absent distally; basal leaf blades palmately veined with 5-7 basal veins, 30-45(-60) × 10-30 cm, veins pubescent primarily along veins with flattened, whitish hairs. Inflorescences 250-500-flowered, 15-40 cm; peduncle 1-8 cm, glabrous. Pedicels articulated at or proximal to middle, 2-5 mm, glabrous. Flowers: tepals oblong-ovate, 2.3-4 × 1-2.5 mm, margins hyaline, apex obtuse. Achenes 6-10(-12) × 6-11 mm including wings, 4-8 times longer than perianth; wings tan, veined, 3-4 mm wide, membranous. 2n = 44.

Nomenclature:

Scientific Name: Rheum rhaponticum L.

Vernacular name(s): rhubarb

Scientific family name: Polygonaceae

Vernacular family name: knotweed.

Geographic Information

Plant or plant parts used in or around the home.

Notes on Poisonous plant parts:

Rhubarb leaves contain the highest amounts of oxalates and perhaps anthraquinones, which may be partly responsible for toxicity. The stalks also contain some low levels of oxalates, but this is not a problem (Cooper and Johnson 1984).

Toxic parts:

Leaves.

Notes on Toxic plant chemicals:

Oxalates are contained in all parts of rhubarb plants, especially in the green leaves. There is some evidence that anthraquinone glycosides are also present and may be partly responsible (Cooper and Johnson 1984).

Toxic plant chemicals:

Anthraquinones, oxalate.

Chemical diagram(s) are courtesy of Ruth McDiarmid, Biochemistry Technician, Kamloops Range Station, Agriculture and Agri-Food Canada, Kamploops, British Columbia, Canada.

Animals/Human Poisoning:

Note: When an animal is listed without additional information, the literature (as of 1993) contained no detailed explanation.

Goats

General symptoms of poisoning:

Diarrhea, mouth, frothing of, vomiting.

Notes on poisoning:

A goat that ate rhubarb leaves stood with outspread legs, an open mouth, and protruding eyes. The animal was crying and produced sour green vomit and profuse diarrhea (Cooper and Johnson 1984).

Humans

General symptoms of poisoning:

Abdominal pains, abortion, convulsions, death, drowsiness, muscle twitching, nausea, vomiting.

Notes on poisoning:

Ingesting rhubarb leaves has caused many fatalities, especially during World War II, when the leaves were recommended as food for a short time. In one fatal case, oxalic acid was ingested at a rate of only 1.3 g/kg, whereas five or six times this amount normally constitutes a fatal dose. More recent evidence indicates that anthraquinone glycosides may be involved. Symptoms include abdominal pain, nausea, vomiting, weakness, and drowsiness. Blood clotting is reduced. A woman in early pregnancy aborted before she died. Two children ingested 20-100 g of leaves and stalks. They vomited and developed jaundice, with some kidney and liver damage. Analysis for oxalate crystals in the urine may help diagnosis (Robb 1919, Cooper and Johnson 1984).

Swine

General symptoms of poisoning:

convulsions

death

gait, staggering

mouth, frothing of

Notes on poisoning:

Swine that ingested rhubarb plants exhibited the following symptoms: foaming at the mouth, staggering, and convulsions, followed by death. Postmortem examination revealed severe inflammation of the stomach and intestines (Cooper and Johnson 1984).