Chi-Guang Wu

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.

Ultrastructural Investigation of Humariaceae (Pezizales, Ascomycetes). II. Ascosporogenesis in Selected Genera of the Ciliarieae

Species of Cheilymenia, Coprobia, and Scutellinia of the Ciliarieae (Humariaceae) are studied by electron microscopy. They share the same type of ascosporogenesis, although only Cheilymenia and Coprobia form spore sheaths on their ascospores, and epispore layers are formed after the primary wall is deposited between spore-delimiting membranes. The manner of formation of epispore layers is very similar to that in the genus Aleuria. Gradual condensation of the secondary wall material in the perisporic sac is consistently found. Globular bodies with rodlet contents are found in the perisporic sac of Cheilymenia and are different from those found in Aleuria. Vacuolation occurs in the perisporic sac, within which ornaments are almost completely formed. During the condensation of secondary wall material, a translucent zone similar to that commonly found in Ascobolus and other coprophilous fungi is formed between the epispore layer and the ornaments.

Ultrastructure of Spore Ontogeny in Trichophaea brunnea (Pezizales)

Trichophaea brunnea is a small, pyrophylic, operculate discomycete with hyaline, uniguttulate ascospores and an excipulum fringed with short, brownish, tapering hairs. Most recent literature places the species in Sphaerosporella because of its smooth spherical spores, as opposed to ellipsoid spores of other species of Trichophaea. Ellipsoid-spored species of Trichophaea have both smooth and ornamented ascospores with variable guttulation and other apothecial characters. These differences raise questions as to the relationship of T. brunnea to other species of Trichophaea. In this article we examine the fine structure of spore wall development in T. brunnea to determine if it is comparable to that of ellipsoid-spored species. We found that while early stages of spore ontogeny are similar, there are differences in staining properties of the primary wall of three species compared, but wall development in T brunnea is much like that in the type T. abundans The pattern of deposition and staining properties of various wall layers support other conclusions that Sphaerosporella should not be recognized as a distinct genus.

Ultrastructure of ascospore ontogeny in Aleuria, Octospora, and Pulvinula (Otideaceae, Pezizales)

Ultrastructural studies were used to help resolve questions as to the recognition and limits of the heterogeneous family Otideaceae (Pezizales). Ascospore ontogeny was examined in species of Aleuria, Octospora, and Pulvinula and compared with that of other members of the order. Stages of ascosporogenesis, including primary wall formation, were similar to those found in other pezizalean genera. An accumulation of electron-dense globules appeared early in the perisporic sac of species of Aleuria and Octospora and contributes directly to formation of the epispore layer. In Pulvinula, there was a late accumulation of small electron-dense granules that was deposited onto the primary wall to form the epispore. A pronounced development of dense granules occurred in the perispore of Aleuria that condensed onto the epispore to form prominent ornaments. In Octospora, the granules degenerated and formed a loose secondary wall separated from the primary wall by an electron-translucent zone. A secondary wall did not develop in Pulvinula, and the epispore layer became the outer spore wall. We conclude that there was not a close correlation in spore ontogeny among the tribes of Otideaceae currently recognized on the basis of light-microscope data.

Ultrastructural Investigation of Humariaceae (Pezizales, Ascomycetes). III. Ascosporogenesis of Mycolachnea hemisphaerica (Tribe Lachneae)

Ascosporogenesis is studied in Mycolachnea hemisphaerica of the tribe Lachneae, Humariaceae. Ontogeny of spore-delimiting membranes, free cell formation, and primary wall deposition in this genus are essentially the same as reported in other Pezizales. During formation of the secondary wall, the matrix of wall material accumulates within the perisporic sac into two zones, an inner, compact zone, and an outer, loosely fibrillar zone. The secondary wall is deposited onto the epispore layer through a gradual condensation of this material in the inner zone. A distinctly ornamented secondary wall is formed in M. hemisphaerica, and there are three different types of inclusion bodies in the sporoplasm. Overall spore ontogeny is very similar to that of species of Trichophaea.

Ultrastructure of Spore Ontogeny in Species of Trichophaea (Pezizales)

Trichophaea (Otideaceae) is a group of small, setose, operculate discomycetes that produce smooth or ornamented guttulate spores and have apothecia without carotinoid pigments. Their relationship to species of Humaria and Tricharina has not always been clear. Recent ultrastructural studies seem to support the inclusion of the spherical-spored Sphaerosporella in Trichophaea, a traditionally ellipsoid-spored genus. In an ultrastructure study of spore development in Trichophaea abundans and Trichophaea paludosa, two patterns of spore development were found, one in T. abundans in which there is no secondary wall in mature spores and another in T. paludosa in which there is a highly ornamented secondary wall. The types of spore development in these species are compared and contrasted with those of other Otideaceae. A reexamination of the limits of Trichophaea is indicated.

Ascosporogenesis in Tarzetta (Otideaceae, Pezizales)1

Ascosporogenesis in Tarzetta is, in many respects, very similar to that of other discomycetes in the Pezizaceae, Helvellaceae, and Morchellaceae. There is, however, no condensation of globular secondary wall material within the perisporic sac, a condition similar to the type of secondary wall formation observed in Pulvinula and Geopyxis (Otideaceae). Two stages in the spore ontogeny of Tarzetta are very distinct from spore ontogeny in other Pezizales: (i) epispore is formed without inclusion of spinelike precursors but instead with interconnecting periclinal fragments, and (ii) an electron‐opaque primary wall (or initial wall) is deposited between two spore‐delimiting membranes. These features of spore ontogeny suggest that Tarzetta may not be as closely related to other genera of Otideaceae, where it has been traditionally placed.

Ultrastructural Studies of Ascosporogenesis in Ascobolus stictoideus (Pezizales, Ascomycetes)1

Ascosporogenesis in Ascobolus stictoideus is studied and compared with that found in other members of Pezizales. Early phases of ascus development involving spore delimiting membranes from the plasmalemma and spore formation within the epiplasm are much like those of other species of Pezizales, with the exception of the appearance of organelles, such as pigmented bodies and net bodies, which are not found in other taxa. Primary spore walls are very thick and electron translucent. Opaque globular bodies, amorphous dense material derived from net bodies, and dense membrane‐bound bodies associated with the endoplasmic reticulum appear in the epiplasm and later play a role in spore wall formation. Dense granular bodies containing small particles are transported from the epiplasm into the perisporic sac along with pigmented bodies. These deeply opaque bodies increase in size, appear to coalesce, and are deposited onto the epispore layer of the spore. The phylogenetic significance of spore wall development is discussed in light of recent molecular data.