DISCUSSION OF THE INOPERCULATE DISCOMYCETES

The Leotiomycetes form a loosely related and very diverse group of fungi having in common more or less openly exposed inoperculate asci. Their diversity makes them difficult to characterize and to subdivide, but the traditional view of them seems to be suported by recent genetic work. In this treatment we assign them to four large orders: the Helotiales, the Sclerotiniales, the Rhytismatales and the Geoglossales. Of course there are some fungi that will seem to fall into the Leotiomycetes without being obviously a member of any of the four orders. And of course some of the orders, particularly the Geoglossales may be only distantly related to the others and fit more comfortably into their own class.

In spite of these reservations most fungi can be assigned to this group without much difficulty. The Helotiales are usually clearly apothecial, with the apothecium resting flat on the substrate (sessile) or raised on a stipe. In some cases, especially the stipitate species, the apothecium may be modified until it no longer resembles one, but these exceptions are not difficult to come to terms with.

The Sclerotiniales nearly always have cup-shaped apothecia. The difference between them and the Helotiales is that their apothecia arise from dark and often tough or hard stromatic tissues. In many cases these take the form of sclerotia, small round and usually black structures. They are all parasites of plants, although this may not be apparent because the apothecia arise from sclerotia occurring in soil on the remains of the host, often in the following season.

The Rhytismatales are all either parasites or endophytes on living plants. They differ from other inoperculate discomycetes in having their asci contained within a hard shell or covering until they are mature. When they are ready to discharge their ascospores the covering splits open to expose the layer of asci. Most species are recognized as dark and often shiny spots on leaves and stems.

The Geoglossales or earth tongues are easy to recognize. All are characterized by long stalks bearing elongated and flattened apothecia. The apothecia are never cup-shaped or discoid.