Using phylogeny and ultrastructure to study cystidia of twoPsathyrellaspecies: reciprocal illumination

Abstract

Ultrastructure of the cystidia of Psathyrella aff. nolitangere (Fr.) A. Pearson & Dennis and Psathyrella rhodospora Weaver & Smith (Agaricales) was examined primarily using freeze substitution, with the goal of evaluating whether these cells could provide phylogenetically informative characters with which to study morphological evolution. Within the Agaricales, the diversity of cystidial form coupled with the limited number of studies makes accurate character coding for use in phylogenetic analyses problematic. This study revealed many common cystidial characteristics between the two closely related species examined, including well-formed apical crystals, abundant free ribosomes, and scattered smooth endoplasmic reticulum. Transmission electron microscopy was used for the first time to examine calcium oxalate crystals in cystidia, and demonstrated the formation of a pre-crystalline matrix at the apex of each cell that possibly disrupts the wall as the crystals form. The shared subcellular traits suggest that ultrastructural details of cystidia may provide additional characters for and signal in phylogenetic analyses.

Systematics and Evolution

“…Specialized cell types, such as cystidia and paraphyses, are also potential sources of characters, but homoplasy may be a problem with interpretation at certain taxonomic ranks (Bellemere 1994;Jenkinson et al 2008;Padamsee et al 2008;Pfister and Kimbrough 2001) but are incompletely surveyed. Host-parasite interactions show remarkable structural variations in some fungal groups and have been used for taxonomic purposes (Bauer et al 2001;Bergerow et al 2006).…”