This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
This is not the place for a discussion of the different genera of the puff-balls, etc., but it might be well to say that in recent years the old genus Lycoperdon has been divided into several genera. The giant buff-ball, and the L. cyathiforme, where the wall or peridium ruptures irregularly, have been placed in a genus called Calvatia; certain other species which are nearly globose, and in which the wall is of a papery texture at maturity, are placed in the genus Bovista. There is one genus belonging to the same family as the lycoperdons, the species of which are very interesting on account of the peculiar way in which the wall is ruptured. This is the genus Geaster, that is, "earth star." The wall, or peridium, is quite thick in the members of this genus, and when it matures it separates into several layers which need not all be discussed here. A thick outer portion which separates from a thinner inner portion further splits radially into several star-like divisions, which spread outward and give to the plant the form of a star. Since the plants lie on the earth the name earth star was applied to them. This opens out in dry weather, even curving around under the plant, so that the plant is raised above the ground. Then in wet weather it closes up again. The inner portion of the wall opens at the apex in various ways, in the different species, so that the spores may escape. A closely related genus has several small perforations like a pepper box in the upper surface of the inner wall, Mvriostoma.