Fungi to observe · Astraeus hygrometricus
Discover the weather earthstar
A star on the forest floor? Flauschi spots an earthstar. Its arms can open and close, and Puschel wonders why.
The short answer
An earthstar has star-shaped arms around a round spore sac. Humid air makes the arms spread; dry conditions close them. This responds to moisture and does not reliably forecast weather.
See the connection
Simplified drawings, not to scale. Not a guide for identifying species.
An imagined Wusel scene
Puschel and Flauschi investigate
Puschel finds something that looks like a tiny star on the forest floor. Flauschi studies it from a distance through her magnifying glass. Flauschi“It is a fungus!” she says. Both marvel at the brown rays around its round centre.
Fungus facts
Three things to notice
Shape
Split outer covering forms star-like rays around a round spore sac.
How it lives
In moist air the rays spread open; in dry air they close again.
In the forest
Weather earthstars can grow on dry, sandy woodland soil near pines.
Try explaining it
What happens to earthstar arms as conditions become dry?
Choose a), b) or c), then explain your choice.
- a)They close around the spore sac.
- b)They open further and expose the ball.
- c)They fall off and regrow after every rainfall.
Show the explanation
Correct: a): They close around the spore sac.
The arms respond to moisture: closed when dry, open when damp. This is not a weather forecast.
Word help
- spore
- A tiny unit that helps fungi or ferns spread. In suitable conditions it can start further development. It is not a seed.
- mycelium
- A network of fine fungal threads, often hidden in soil or wood.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
Can a fungus predict the weather?
The outer covering splits into star-like arms. These respond to moisture: they spread in damp conditions and can close around the spore sac when dry. The material’s properties produce this movement. The fungus is not thinking about tomorrow’s rain.
Compare and understand
Spores lie inside the rounded centre and can escape through a small opening. Arms and spore sac therefore have different roles. The name does not promise a reliable forecast. Observe existing forms or photographs rather than collecting or wetting a fungus to make it open.
Sources for this explanation
An optional question for further exploration
You can use the longer explanation above. This is extra, not needed for the first quiz.
Mini quiz
An extra question
After damp air, conditions become dry. How do the earthstar’s arms respond?
Show answer
They close around the spore case. In damp air they spread open again.