Mesozoic and younger rocks contain numerous examples of ascomycetous fungi (Taylor, 1994), many of them preserved on compressed leaves. Epiphyllous fungi are commonly encountered on many forms of vegetation as early as the Cretaceous, and probably far earlier, although few good examples exist. Despite the tremendous diversity of foliage types during the Carboniferous, for example, there are very few reports of fungi associated with the leaves. One example is reported in cuticle preparations of rachides and pinnules of Callipteridium, a pteridosperm from the Stephanian of France (Krings, 2001). The fungus consists of septate hyphae, but no reproductive structures were found. In preservation of this type, it is especially difficult to determine if the fungus was associated with the plant when it was alive, or simply represents a saprotroph that colonized decaying plant remains. As is true for many facets of paleomycology, epiphyllous fungi in the Paleozoic may exist, but have simply been overlooked. If this is not the case, perhaps the plants possessed chemical substances that deterred epiphyllous fungi, or fungi simply may not have evolved an epiphyllous habitat by the Paleozoic.
Stomiopeltites is perhaps the oldest (Early Cretaceous), well-documented member of the Dothideales (Pezizomycotina, Ascomycota), a group that includes numerous epiphyllous taxa (Alvin and Muir, 1970). It consists of dome-shaped plect-enchymatous thyrothecia (a type of ascocarp with a palisadelike layer of hyphae), each bearing a small ostiole. Hyphae are small (1.7-3 pm in diameter) and form the layered wall of the thyrothecia. Pycnidia (asexual reproductive structures) are common and appear to have been borne directly over a stoma on the leaf surface. No spores were described in these specimens. This fungus is unique, not only because of its age but also because it is one of the few fossil epiphyllous fungi known to occur on conifer leaves (Frenelopsis). Stomiopeltites (FIG. 3.104) is also known from the Upper Cretaceous (Cenomanian) of France, also on Frenelopsis leaves (Pons and Boureau, 1977) (FIG. 3.105), and from the Miocene Clarkia locality of Idaho, USA, on leaves of three angiosperm genera (Phipps and Rember, 2004).
Numerous structurally preserved ascomycetes have been described from Cretaceous conifer leaves of the Brachyphyllum-type (Van der Ham and Dortangs, 2005). The fossil fungi (FIGS. 3.106, 3.107) are thought to be
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