March Weed of the Month: Edible Plants that have Poisonous Parts

In Minnesota, we have some poisonous plants commonly growing in home and community gardens of which we can safely eat certain parts (like tomatoes or other nightshades). In this article we will focus on a few of these vegetable and fruit crops that have poisonous parts—Nightshades, Prunus species, and Rhubarb.

The Solanaceous family, also known as the Nightshade family, includes such plants as tomato, potato, pepper, and eggplant. These plants all contain the toxin solanine in varying amounts in the green plant parts. The leaves of Solanaceous plants usually must be ingested in large quantities to produce harmful effects in humans and animals. Potatoes have the potential to be the most dangerous; tubers that have turned green and/or sprouted due to sunlight exposure or improper storage have high amounts of solanine, and should *never* be eaten. A small percentage of the population is allergic to Solanaceous fruits. For some with sensitive skin, brushing against the hairy and resinous leaves can cause irritation or rash.

The Prunus (stone fruit) family includes plum, cherry, apricot, almond, and native fruit trees like chokecherry, black cherry, and wild plum. These trees all have trace amounts of cyanolipids in the leaves and amygdalin in the seeds. These compounds can be converted into the toxin cyanide when the leaves are crushed and exposed to air (as after mulching or chipping) or upon chewing and digestion. After this decomposition process, poisonous amounts of cyanide may be released. Accidental poisoning may occur in humans, especially by curious children, but it most commonly occurs in livestock and pets. The smaller size of dogs and cats can make them particularly susceptible.

Rhubarb ("Rheum rhabarbarum") is a beloved vegetable grown in Minnesota’s home and community gardens. An herbaceous perennial with thick rhizomes, it is grown for its tart, fleshy stalks. Most people do not realize that rhubarb’s leaves contain oxalic acid, among other unidentified poisonous substances. The stalks contain trace amounts of this compound but are obviously safe for consumption. There are a number of references to accidental poisonings occurring in Europe during World War I, as the rhubarb leaves were apparently recommended as food during the scarcity of wartime. People must ingest large quantities of leaves to experience the toxic effect, but small animals like cats and dogs can fairly easily ingest too much.

We clearly are intimately linked to these plants and will continue to grow and harvest from them in our home and community gardens. With the knowledge that specific plant parts can be harmful to pets or children if ingested, we should use them with precaution. Please contact Minnesota Poison Control with any concerns about potential human poisoning at 800-222-1222, poisonhelp@hcmed.org, or http://www.mnpoison.org [ http://www.mnpoison.org/ ].