Finding the Hygroscopic Earthstar at Wakakusayama Hill

Discover the Astraeus, a rare and fascinating mushroom in Nara's deer park. Learn about its unique features and why it's so special.

This post will be about one specific species I found that I was fortunate enough to stumble upon last week while re-exploring the Wakakusayama Hill: わかくさやま in Nara.  

I have many memories of this place (before my interest in fungi), and this would mark my third visit to this deer-laden park.  

It’s always interesting to return to a familiar place to explore more of the side trails and get a better feel for the landscape. Dusting off the cobwebs and recollecting familiar sites, even if it’s been five years - is mentally rewarding.  

I make my way up the hill the long way and start my more attentive scanning of the hillsides.  

Astraeus sp.

I’ll share all of what I found in a later post, but for now, we’ll stick to the Astraeus hygrometricus—also known as the hygroscopic earthstar, barometer earthstar, or false earthstar. 

Astraeus shares a superficial resemblance but differs genetically and in microscopic characteristics, unlike the true earthstars of the genus Geastrum.  

Astraeus sp.

The fungus is notable for its ability to absorb water and open or close its rays in response to humidity changes.  

I took a video, and in it, you can see reddish-brown spores.  

While generally considered inedible in North America, it is consumed in parts of Southeast Asia.  

Research has highlighted the mushroom’s potential in immunomodulation and cancer treatment. Polysaccharide extracts show anti-tumor properties and stimulate immune cells in mice.

In traditional medicine, Astraeus hygrometricus has been used externally to stop bleeding and reduce chilblains in Chinese medicine, as a salve for burns by Indian forest tribes, and culturally by the Blackfoot of North America, who regard it as “fallen stars” with supernatural significance.  

It is a bit uncanny, but after finding this species, I got a message from my friend Eric from Taiwan. He shared with me multiple research papers that distinguish different varieties of the false earthstars that they have in the region.  

"Identification of Japanese Astraeus based on morphological and phylogenetic analyses" investigates the diversity of Astraeus fungi in Japan by examining 35 collections from Japan and Thailand through morphology and rDNA ITS sequence analysis.

It identifies two distinct Japanese Astraeus groups, differing in basidiome size, exoperidium shape, and spore size. Phylogenetic analysis confirms these groups belong to separate clades, with one closely related to Astraeus hygrometricus var. koreanus and the other representing an undescribed species.

Another similar looking species is Astraeus ryoocheoninii, a mushroom first discovered in Korea's Demilitarized Zone (DMZ).

To make it even weirder, later that evening, I received a message from my friend Jerry that she was eating “spicy puffball mushroom” soup in Thailand. She sent me photos, and I’m scratching my head.

แกงเห็ดเผาะ / young Astraeus sp. - puffball mushroom soup

I don’t know what they are at first sight, but when I reverse image search the menu, and translate the Thai text for the mushroom (แกงเห็ดเผาะ), lo and behold, it’s the same Genus! —Astraeus.  

I’m led to a YouTube video where locals collect heaps of juvenile false earthstars that haven’t yet opened.

Stumbling upon Astraeus sp. and then watching it magically appear in friends' lives across the globe is like the stars aligning in the world of fungi. It’s a coincidence that highlights interconnectedness, driven by a shared fascination with nature.