The family members thought that they were eating Tetragonia, or New Zealand spinach, but were instead ingesting a toxic plant known as Devil's weed.
French sanitary authorities are warning people not to confuse wild toxic plants and edible ones after four members of a family were sent to intensive care after ingesting what they believed to be spinach.
The four relatives from eastern France were hospitalised earlier this month after presenting "signs of severe poisoning," the country's food safety agency, ANSES, said in a statement.
"While the clinical course was favourable for these four people, one required prolonged medical care," it added.
The family members thought that they had grown Tetragonia or New Zealand spinach — a vegetable considered to be "forgotten" because it is now rarely cultivated.
They bought seeds from a botanical shop last year, which failed to sprout but noticed a year later that small shoots had emerged and assumed it was the Tetragonia.
Unfortunately, the shoots turned out to be that of the deadly Datura plant, also known as Devil's weed or Hell's bells, a perennial that easily sprouts in fields and wasteland and that gardeners also use in their potato patches to poison Dolyphore larvae.
Not realising their mistake, the family included Datura in a dish they ate.
Anses stressed in its statement that "every part of the plant is poisonous and can cause serious or even fatal health effects".
Clinical signs of Datura poisoning appear within an hour and include digestive disorders (nausea and vomiting), dry mouth, acceleration of the heart rate, dilation of the pupils, and hallucinations which may then lead to seizures and a coma.