The first exact knowledge as to the origin of the ascocarp was the work of Stahl on Collema in 1877.
The Ascolichenes are again divided into Pyrenocarpeae or Pyrenolichenes and Gymnocarpeae or Discolichenes; the first having an ascocarp of the nature of a perithecium, the second bearing their ascospores in an open apothecium.
Various types of ascocarp are characteristic of the different divisions of the Carpoascomycetes: the cleistothecium, apothecium and perithecium.
They are characterized by an ascocarp without any opening to the exterior, the ascospores being set free by the decay or rupture of the ascocarp wall; such a fruit-body is termed a cleistothecium (cleistocarp).
De Bary brought forward very strong evidence for the origin of the ascocarp in Sphaerotheca and Erysiphe by a sexual process, but Harper in 1895 was the first to prove conclusively, by the observation of the nuclear fusion, that there was a definite fertilization in Sphaerotheca Humuli by the fusion of a male (antheridial) nucleus with a female, ascogonial (oogonial) nucleus.
Used in its widest sense this includes the Hysteriaceae, Phacidiaceae, Helvellaceae, &c. The group is characterized in general by the possession of an ascocarp which, though usually a completely closed structure during the earlier stages of development, at maturity opens out to form a bowl or saucer-shaped organ, thus completely exposing the layer of asci which forms the hymenium.
Such an ascocarp goes by the name of apothecium.
Is characterized by a special type of ascocarp, the perithecium.