Basidiospore Wall Ultrastructure of the False-Truffle Hydnangium and Its Phylogenetic Significance

Abstract

in basidiomycete systematics. Arguments for and against including false truffles in the Agaricales hinge on the interpretation ofthe character suites and the degree of importance given to them in forming phylogenetic hypotheses (e.g., Kuhner, 1980, 1984; Julich, 1981; Singer, 1986). A number of mycologists have postulated a close relationship between the false-truffle genera Hydnangium Wallr. and Podohydnangium Beaton, Pegler, & Young and the mushroom genus Laccaria Berk. & Br. (e.g., Pegler and Young, 1979; Kuhner, 1980, 1984; Julich, 1981; Beaton et al., 1984; Mueller, 1992; Mueller and Ammirati, 1993) based on similar basidiospore or? namentation. There are numerous publications illustrating basidiospore ornamentation as viewed under the scanning electron microscope for one or more of these three genera (e.g., Pegler and Young, 1969, 1971, 1979; Beaton et al., 1984; Castellano et al., 1989; Mueller, 1991, 1992). Kuhner (1980, 1984) reported that the discrete, conical echinulae observed on basidiospores of both Laccaria and Hydnangium have microfibrils that run nearly parallel to the axis of the spine. He used these wall ultrastructure features, along with cytological and ecological characters, to justify placing Hydnangium and Laccaria in the same family Hydnangiaceae in his Tricholomatales (Kuhner, 1980, 1984). Based on unpublished micrographs of Hydnangium, Mueller (1992) and Mueller and Ammirati (1993) argued that this type of basidiospore wall ultrastructure is the one shared derived morphological feature that links these genera. However, while illustra? tions of the basidiospore wall ultrastructure of Laccaria were presented in Besson and Kiihner (1971) and Kiihner (1980), to our knowledge, no transmission electron micrographs showing the basidiospore wall ultrastructure of Hydnangium or Podohydnangium have been published. In this paper, we present micrographs documenting the similarity of wall ultrastructure of Hydnangium and Laccaria and discuss the phylogenetic implications of these data. Scanning electron micrographs were taken at the Field Museum of Natural History following the procedures outlined in Mueller (1991,1992). For examination on the Uppsala University Jeol 100 B transmission electron microscope, small pieces of lamellar tissue from air-dried herbari? um specimens were rehydrated in 3% KOH, fixed in 2.5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.5), and washed in buffer three times. The samples were then postfixed in 2% Os04 in 0.1 M phosphate buffer for 2 h at 4 C, washed in buffer three times, dehydrated in a graded eth? anol series and propylene oxide infiltrated with Epon, and embedded in Epon that was polymerized for 48 h at 60 C. Sections of 50 nm thickness were cut with a Dupont diamond knife