The genus Astraeus, based on Geastrum hygrometricum Pers., was included in the genus Geaster until Morgan9 pointed out several differences which seemed to justify placing the fungus in a distinct genus. Morgan pointed out first, that the basidium-bearing hyphae fill the cavities of the gleba as in Scleroderma; second, that the threads of the capillitium are long, much-branched, and interwoven, as in Tulostoma; third, that the elemental hyphae of the peridium are scarcely different from the threads of the capillitium and are continuous with them, in this respect, again, agreeing with Tulostoma; fourth, that there is an entire absence of any columella, and, in fact, the existence of a columella is precluded by the nature of the capillitium; fifth, that both threads and spore sizes differ greatly from those of geasters. For these reasons, Morgan stated that it is impossible accurately to define the genus Geaster and still place this fungus in it.
Proceedings of the Iowa Academy of Science
©1951 Iowa Academy of Science, Inc.
Ervin, Marion D.
"Astraeus and Geastrum,"
Proceedings of the Iowa Academy of Science, 58(1), 97-99.
Available at: https://scholarworks.uni.edu/pias/vol58/iss1/9