Geastrum triplex Collared Earthstar
In the photo you can see several developmental stages of the Collared Earthstar. The young fruitbodies are in the foreground and are nearly buried. On the left you see an older stage where the fleshy outer wall (= peridium) has started to split and reflex. In the centre of the field the mature fruitbody is now above the surface and the flesh of the outer wall has split to form a collar around the base of the spore sac.
In Geastrum the fruitbodies are buried in the loose organic duff on the forest floor. As the arms reflex they push against the matrix around them and thus lever themselves upwards. In this way the mature fruitbody eventually sits on top of the duff. This gives the fungus a more advantageous position for dispersal of its spores. Spores are spread in the same way as Lycoperdon.