Phylogenetic, systematic, and morphological studies of the mushroom genus Psathyrella

Psathyrella is the archetypal little brown mushroom genus, found worldwide, with few easily discernable characters. While molecular studies have demonstrated that mushroom genera based on homoplastic morphological characters are artificial, the degree of phylogenetic heterogeneity contained within Psathyrella and Psathyrellaceae has never been appropriately addressed. For Chapter 1, 132 nuclear ribosomal large subunit DNA (LSU) sequences from approximately one-tenth of the known Psathyrella species worldwide and three closely related coprinoid genera (Parasola, Coprinopsis, Coprinellus) were utilized to evaluate phylogenetic relationships in Psathyrellaceae. The results indicated that Psathyrella was polyphyletic. Most species of Psathyrella, including its type species P. gracilis, formed a large clade with Coprinellus, which appeared to be derived from within Psathyrella . The results were interpreted in light of the two major taxonomic treatments of Psathyrella and revealed substantial inconsistencies between the molecular- and morphology-derived inferences of relationships. Psathyrella can be separated into 11 clades of which five can be raised to generic status. One of these clades was the basis for Chapter 2 and circumscribed as a new genus in Psathyrellaceae based on a combination of microscopic features and molecular phylogenetic evidence. This genus consists of psathyrelloid mushrooms with red, smooth spores that typically also possess thick-walled encrusted cystidia, phylogenetic analyses of LSU and elongation factor 1-alpha sequences confirmed the placement of these species as the sister group to fungi with ornamented-spores in the genus Lacrymaria. Reddish spore pigmentation seems to be associated with the presence of cystidial encrustations within the new genus. For Chapter 3, ultrastructure of the cystidia of two species within the planned new genus, Psathyrella nolitangere and P. rhodospora, was examined using primarily freeze substitution with the goal of evaluating whether these cells could provide phylogenetically informative characters to study morphological evolution. This study reveals many shared cystidial characteristics between these two closely related species, including the manner of extracellular calcium oxalate crystal formation and organization of cytoplasmic content. The conserved subcellular traits suggest that ultrastructural details of cystidia may provide additional characters for and signal in phylogenetic analyses.