Pteridomania was a fearsome ailment. Symptoms caused women to swoon and fall off of cliffs—and entire species to fall into endangered status. But the contagious disease wasn’t one of the body: “Fern fever” was a fad that swept through England during the 19th century. 

Not so surprisingly, a botanist was to blame for the craze. In 1829, Nathaniel Bagshaw Ward had given up trying to grow ferns in the polluted London air, and had moved on to studying moths. But when studying a chrysalis that he kept in a covered glass bottle, he noticed that ferns began to grow in the soil at the bottom of the jar. Ignoring the moth, he began to experiment with tightly-sealed glass cases

To modern-day readers, there’s nothing sexy about a terrarium, but Wardian cases,” as they became known, were big news for Victorians. Suddenly, it was possible to grow and study plants indoors—a feat helped along by quick industrialization, which made such devices accessible to ordinary people. People started to mail-order exotic ferns to grow at home and set out in search of the perfect specimen. 

Ferns had long been associated with the female sex, bringing to mind moist nether regions and shady places. Certain types of fern are even referred to as maidenhair—an overt reference to pubic hair. 

It turns out that ferns’ sex lives are just as bizarre as the idea of fern fever sweeping an entire nation. As NPR’s Geoff Brumfiel recently reported, at least one species of fern emerged from the unexpected mating between two different fern species that lived and flourished in completely different places and were “separated by nearly 60 million years of evolution.” 

Fern-o-mania’s biggest proponents were young women, who took to fern hunting, preservation, and growth in large numbers. Charles Kingsley dubbed the phenomenon Pteridomania, complaining that “Your daughters, perhaps … [are] wrangling over unpronouncable names of species, (which seem to be different with every new fern that they buy), till the Pteridomania seems to you something of a bore.” 

In the socially-acceptable pursuit of ferns, young women could get outdoors, often without the strict chaperonage of indoor activities. They could have adventures and compete with one another. They also could run into trouble: In her book The Bronte Cabinet: Three Lives in Nine Objects, Deborah Lutz writes about a fern-seeker named Miss Jane Myers who plummeted 170 feet to her death while gathering ferns. 

But the relentless pursuit of all things fern had a downside: It led to dramatic depopulation of native fern species in the UK. Species like the Killarney fern still suffer from the effects of the craze today—an unexpected dark side to what seems like a harmless obsession.