The four women ended up in the intensive care unit of a hospital in eastern France after eating datura leaves, a toxic plant also known as the Devil's weed and Hell's bells, said the French food safety agency, Anses.
“Four people from the same family cooked a dish using datura after confusing its leaves with New Zealand spinach they had planted in their garden,” the agency added.
All four showed symptoms of “serious poisoning” which can include fever, hallucinations, psychosis, convulsions and sometimes kidney failure.
They all recovered though one “will need long-term monitoring”, the agency said.
Datura has traditionally been used in witchcraft and sorcery in many cultures, and is commonly planted at the end of rows of potatoes in organic permaculture to kill Colorado beetle larvae.
The women had sown the New Zealand spinach grains in their garden the previous year, an Anses statement said, “but it did not grow when they thought it would.
“A year later they noticed little leaves popping up at the spot where they had planted the seeds” and assumed it was the spinach, it added.
The vegetable, known as tetragon or Cook's cabbage after the English explorer, prefers warm conditions and doesn't normally grow until the soil has warmed up.
The agency warned that datura grew widely across France and that “all parts of the plant are toxic and can have serious and sometimes fatal effects.”
Symptoms usually start to appear an hour after the plant is eaten.
Last year, the French supermarket chain Leclerc was forced to recall two consignments of frozen French beans because of the risk that packets also contained datura.