• You’ve probably used oxalic acid many times in your life, as it’s one of the main ingredients in rust removers, metal cleaners, and bleach products. It’s produced on an industrial scale through chemical means. It’s very caustic and causes blistering when it contacts human skin. But oxalic acid is also present in plants.
• It’s named for the genus of plants called Oxalis, which includes wood sorrel from which it was first extracted. The shamrock plants popular in stores around St. Patrick’s Day are also members of the Oxalis genus.
• But oxalic acid is also found in other plants as well. Many species of fungus excrete oxalic acid into the soil, which makes minerals more available to plant life. Most fruits, veggies, nuts, and seeds contain oxalic acid. Humans can digest oxalic acid in normal amounts.
• Rhubarb stems contain oxalic acid, but rhubarb leaves contain enough of it to make a human ill if enough of it is consumed. However, chard and spinach contain even more than rhubarb. People eat chard and spinach all the time without getting sick, so how did rhubarb leaves get such a bad rap?
• During World War I, a well-intentioned but misguided government agency sent out an advisory encouraging its citizens to eat rhubarb leaves to alleviate food shortages and help the war effort. After sicknesses and one possible death was reported as a result, the recommendation was rescinded. Word spread that rhubarb leaves were to be avoided at all costs. The bad reputation kept on growing.
• Rhubarb leaves are not instantly poisonous; it would take constant prolonged exposure to eventually die by kidney failure. To reach a lethal dose in a single sitting, a 143-lb (65 kg) human would have to eat 18 lbs (5 kg) of leaves all at once. Such a feat would be unlikely because swelling of the throat and mouth, along with nausea, would end the meal long before the danger of death arrived.
• Symptoms of mild rhubarb leaf poisoning include vomiting and diarrhea that resolve within a few hours. More serious oxalate toxicity causes sore throat, difficulty swallowing, nausea, and abdominal pain. Prolonged exposure to oxalic acid interferes with the body’s calcium metabolism, because oxalic acid binds with the body’s calcium, removing it from the blood, forming kidney stones, and leading to kidney failure.
• Still, spinach and chard are equally bad if eaten in the same amounts.
• Rhubarb is a leaf stalk, like celery. Although it is botanically a vegetable, it’s classified as a fruit in the United States.
• The rhubarb plant is hard to kill. It thrives in cold inhospitable climates including Siberia, Mongolia, and Alaska. It originated on the mountain slopes of China, where Marco Polo noted it growing prolifically.
• At one point during medieval times, it was worth more than such valuable substances as cinnamon, saffron, and opium.
• The words “baby,” “babble,” and “barbarian” all spring from the Greek word “barbarous” meaning a foreigner or one who speaks an incomprehensible language. It’s the same story for the rhubarb plant. The land along the river Volga was known to the Greeks as the Rha. Since this was an unknown territory, they called it “barbaron” or barbarian. A plant they found there was dubbed “rha barbaron” meaning “from the barbarian land of Rha” and then shortened to rhubarb.
• Benjamin Franklin brought rhubarb to America when he shipped some samples to American botanist John Bartram from Europe in 1771. Thomas Jefferson promoted it.
• In a poll, Americans voted apple pie to be their favorite, but rhubarb pie came in second place, beating out pumpkin, cherry, blueberry, and key lime.