It’s the latest craze in a country known for its eccentric tastes and quirky obsessions. The Japanese have gone gaga for…moss?

In 2011, Hisako Fujii published a book titled Mosses, My Dear Friends. It went on to sell over 40,000 copies, which helped trigger a wave of moss viewing parties among young women who call themselves “moss girls.”

Since then, according to The Wall Street Journal, moss-themed drinks and rings that sprout moss instead of gems have joined moss balls (marimo) as popular wares. Now moss devotees can go on special tours, during which guides lead small groups of fanatics deep into Japan’s lush, mossy forests, where they inspect the plants with magnifying glasses.

So what’s behind Japan’s moss craze? Is it a random, flash-in-the-pan fad? Or is it more deeply rooted in Japanese values, customs and aesthetics?

Eastern sensibilities

Of the roughly 12,000 species of moss worldwide, Japan possesses a whopping 2,500 varieties—a relative windfall for enthusiasts devoted to tracking down, studying and documenting their different forms. Japan’s humid climate creates the perfect conditions for the plant to thrive, and gazing at moss during Japan’s hot, humid summers can actually have a relaxing effect (one reason many will hang moss balls under the eaves of their houses).