Ultrastructural Evidence for a Phylogenetic Linkage of the Truffle Genus Hydnobolites to the Pezizaceae (Pezizales, Ascomycetes)

Hydnobolites cerebriformis is a widespread species of hypogeous ascomycetes found in both the United States and Europe. The ascomata are from 0.5 to 3.0 cm in diameter, with a thin cortical region surrounding clusters of globose to saccate asci arranged near veins within the medullary region. Because hymenial chambers were believed to lead to the surface of the ascomata, the genus was until recent years placed among Tuberaceae. The size, shape, and arrangement of asci and the pigmentation of ascospores, however, have led recent workers to place Hydnobolites in the Terfeziaceae. Cytological and ultrastructural features of asci, septa, and spore wall ontogeny in H. cerebriformis reveal a number of characters that link Hydnobolites to the traditional epigeous Pezizaceae. These include the presence of electron-dense, biconvex bands in septal pores of asci, dextrinoid and weak bluing reaction of asci in iodine, and a type of spore wall deposition similar to members of Pezizaceae.