Q What’s the strange star-shaped fungi under our ash trees?
Carol Brodie, Whitchurch, Buckinghamshire
A These sound like earthstars. There are 18 species of earthstars in the UK, but most are quite rare. The most common species, the collared earthstar ( Geastrum triplex), however, is quite often encountered in areas of deciduous trees. Earthstars are saprotrophs, growing on dead organic matter, and are found in the leaf litter beneath trees, producing these quite unusual mushrooms during autumn. The outer shell opens out to reveal the thin-walled sac in the middle.
In the case of the collared earthstar, when the outer casing folds out like the petals of a flower, a crack emerges near the centre, giving the appearance of a collar around the spore sac. When rain or wind disturbs the earthstar, spores are released through an opening at the top.