Using phylogeny and ultrastructure to study cystidia of two Psathyrella species: 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.