Winter Botany Study, Part 6: Hygroscopic Earthstars



While anxiously looking for signs of spring, I was rummaging about under a scrub live oak yesterday just to see if that somewhat warm and protected site was harboring anything green. No luck, yet! But what I did find was small woody star sitting on top of the duff. Instantly I knew what it was (or so I thought). Always curious, the “star” made the trip home where I began poking and prodding and perusing the internet and my collection of mushroom field guides. Prepared to confirm my belief that this was the woody husk of a Puffball, after a few hours research I discovered how wrong I was. How the old adage, close is only good in horseshoes, is very true and that jumping to conclusions is often misleading. Oh really? puffball fungi don’t have woody husks! Time to geek out, again!

My love of rabbit-trailing led me right past puffball fungi (which lack the signature star structure, aka ”woody husk) to a very similar fungus called an Earthstar. But even that wasn’t quite right. True earthstar characteristics don’t match up with the peculiarities of the little star I had collected. Coloration, size, arrangement of the star rays, and site description were all wrong.

Then I discovered the False Earthstar. Not a catchy name, but no matter. What a fascinating life this little fungus species has. Astraeus hygrometricus, hygroscopic earthstar or barometer earthstar, lives in association with oaks and pines where the mycelium of the fungus helps trees obtain difficult-to-extract soil nutrients in exchange for photosynthetic carbohydrates that the fungus needs and can’t make for itself.

What is equally fascinating is the slow dance this false earthstar performs as it matures. As a young fruiting body climbing out of the soil, to the cracking and spreading of the woody rays exposing the immature white spore case, to the push-ups the rays do to hoist the mature brown spore case up into the wind to spew out its spores, this dance must be something to witness!

Astraeus hygrometricus was named for its hygroscopic behavior. The rays open in response to moisture and humidity; they close in dry conditions. When the opened rays push the spore case up into the wind, environmental conditions are ideal for optimal spore dispersal. But with so many dry dry dry days in central New Mexico (I’m talking less than 10% humidity), if the rays remain closed more than they are open, how do the mature spores disperse? Because they do mature, over time and need to go. Could it be that the entire fruiting body dries up enough to be carried by the wind, spilling spores hither and yon?

Hmmmmmmmm! What are your thoughts?

While you’re thinking, remember to get on out there and explore out world!

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