The patients started trickling in not long after the refugees arrived: Some had painful cramps, others suffered from vomiting or dehydrating diarrhea. In some, their livers had completely stopped working. Some were already close to death.

These were men and women who had survived catastrophic civil war in their home country, a dangerous land or ocean crossing into Europe, and days of walking through fields littered with land mines and on roads barred by police officers wielding water cannons. The fact that they were in Germany at all represented something of a defiance of the odds.

But now, in one of the nations that is thought to be most welcoming to asylum-seekers, they faced another deadly hazard.

Poisonous mushrooms, the doctors diagnosed it. According to a warning issued by Hanover Medical School in northern Germany, more than 30 refugees have been sickened after eating “death cap” mushrooms — a species so toxic a small amount of it can cause organ failure in a matter of days. The New York Times reported that similar cases have been seen in Müntser, a two-hour drive west.

“Do not collect mushrooms, if you are unfamiliar with edible growing mushrooms here,” warned the flier, which was printed in Arabic, Kurdish and other languages, according to the Times. “A mushroom you regard from your homeland as a delicious edible mushroom could be deadly here although they look similar.”

According to the Associated Press, most of the refugees sickened by the mushrooms were Syrian. The death cap, formally known as Amanita phalloides, bears a resemblance to mushrooms that grow in the eastern Mediterranean. Its unassuming shape and white coloring are easily mistaken for edible species, and its taste is innocuous, even delicious.

To make matters worse, it takes several hours for the fungus’s deadly poisons — compounds known as amatoxins — to reach the liver, where they do the most damage. By the time someone starts to feel sick, they may have no idea that the lowly little mushroom they ate half a day ago is the source of their illness.

The North American Mycological Association (the death cap is an invasive species here) says that fatality rates from amatoxin poisoning are about 50 percent without prompt treatment.

The fear is that, after days on the road with little to sustain them, refugees have resorted to foraging for food. It is the middle of its three-month growing season in Europe, and the poisonous mushrooms could sicken still more people.  Dr. Michael P. Manns, chairman of the department of gastroenterology, hepatology and endocrinology at Hanover Medical School, told the Times that 12 patients remained hospitalized on Thursday, three of them in critical condition.

“Please do inform others in and around your accommodation,” the medical school’s warning reads. “In this way you save lives!”