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The Earthstar Mushroom (Geastrum)

Look at this mean green mother from outer space! Well... it isn't green... nor is it from outer space. But looking at these odd-shaped and conveniently named fungi, you would not be blamed for thinking otherwise. So what is this genus, and what can we learn about it?

Physical Description and behavior

This mushroom genus tends to be rather small, often being far less than 3 inches in diameter. Many being far smaller than 2 inches in diameter when mature. They are often less than an inch tall as well. They are usually a brownish-cream color but can be darker in some species. The inner "petals" can be a cream color, bright white, or like Geastrum rufescens, can have a reddish hue.

The bulb on the inside is actually a spore sac, which has a small opening on the top. This hole can either be plain or have a ring around it that looks akin to a human nipple. Spores often escape from this sac when it rains. This often damages the sac, giving it a more flattened or crushed appearance.

Fun fact: This mushroom starts out as a pod, or bud, and bursts open ("blooms") as it ages. This is known as dehiscence. This is believed to be due to a buildup of calcium crystals that occurs right before opening. As it opens, it forms a starlike pattern, hence, its name. Another aspect that contributes to the opening is water. After Geastrum splits, the "petals" close in on themselves as it begins to dry out, but opens like a flower when the fungus is hydrated again. This is known as hygroscopy.

While this fungus is not considered to be toxic, they are considered to be inedible due to their hard, fibrous nature and bitter taste.

Habitat and Location

This genus was thought to have just 50 species to its name, but research conducted in 2014 indicates there may be as many as 120 different species. These species can be found just about all over the world, mainly in the US, South America, and Europe. However, they can also be found in fewer numbers in Australia, New Zealand, Africa, Asia, and India.

They prefer to grow on the roots of hardwood trees and conifers. While preferring deciduous woodland and well-drained soil, they can also be found just about anywhere from dunes to roadsides.

If you want to see this mushroom "bloom" check out the video below!

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