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Earthstar Fungi

Making a living in PEI’s coastal habitats isn’t easy. Conditions are harsh: temperature extremes, salt spray, low organic matter, and scarce freshwater. Plants and fungi found here have developed amazing adaptations, and some of my favourite examples are found in these lovely Earthstars (Astraeus smithii).

Photo 1: Earthstars scattered across an older, stable sand dune. On the right side of the photo is Woolly Hudsonia (Hudsonia tomentosa). Earthstars are always found in association with this plant on PEI.

Earthstars are fungi, and – as with mushrooms – the above-ground part we see is just the fruiting body, like an apple on a tree. The fungus itself is a mass of thread-like tissue (called mycelium) in the soil. Earthstars are mycorrhizal, forming relationships with some of the plants around them. On PEI, Woolly Hudsonia (Hudsonia tomentosa) is always present where Earthstars are (it’s the plant with the yellow flowers on the right side of Photo 1). Earthstars get food from the plants in exchange for providing them with soil nutrients and water. In this dry, nutrient poor, sandy environment, that’s a big help.

Photo 2: The outer layer of Earthstars split open into star-like arms, giving this fungus its name.

In late summer and fall, this fungus begins to send up fruiting bodies. These amazing packets of spores can overwinter, and in summer you can find last year’s Earthstars scattered across the sand (Photo 1). The inner layer is a puffball-like sac that contains the spores; the outer layer splits open with star-like arms, hence the name Earthstar (Photo 2).

That outer layer is hygroscopic – it responds to changes in humidity and moisture. In wet conditions, the arms open and raise the spore sac above the surface of the ground (Photo 3). This does two things: it ensures the spores are dispersed when weather conditions are right, and it elevates the sac to better enable wind to catch and disperse the spores. Each Earthstar can open and close repeatedly as moisture changes. You can see this yourself by putting a few drops of water on one; the fungus will slowly open over several minutes (you can’t really see it move, but when you look away and look back again, you’ll find it has opened a bit more). In dry weather, the closed-up Earthstars are easily moved by the wind, further helping the fungus disperse.

Photo 3: Those star-like arms open in respose to humidity or moisture in the environment.

On PEI, I’ve only ever found Earthstars in older, stable sand dune habitat. These sensitive areas are also home to several Provincially rare plant species (including the previously mentioned Woolly Hudsonia) and some Nationally at-risk plants. I don’t recommend people wander through these sites looking for Earthstars. I’m lucky to be doing some botanical work in a few of these areas this summer, and I’ll be bringing you more of the cool plants that live there in future posts.

Fungi in general, and Earthstars in particular, are fascinating parts of PEI untamed!

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