Disentangling the Collema-Leptogium complex through a molecular phylogenetic study of the Collemataceae (Peltigerales, lichen-forming Ascomycota)

Abstract

Family Collemataceae (Peltigerales, Ascomycota) includes species of cyanolichens with foliose to fruticose or crustose thalli, with simple or septate ascospores. The current classification divides this family into two groups on the basis of ascospore types. The objective of this study was to evaluate the phylogenetic relationships within this family. Combined DNA sequence data from the nuclear large subunit and mitochondrial small subunit ribosomal RNA genes were used to evaluate monophyly of the family and the relationships between the largest genera of this family. The results revealed that this family is not monophyletic. Genera Staurolemma and Physma, currently classified within the Collemataceae, were found nested within the Pannariaceae. The second result of this study confirms that the genera Collema and Leptogium, both part of the Collemataceae s. str., are not monophyletic and that the presence of a thallus cortex is not a synapomorphy for Leptogium. The main taxonomic conclusion is that families Collemataceae and Pannariaceae were recir-cumscribed in light of molecular findings with the latter family now including Staurolemma and Physma. Genera Collema and Leptogium form a single mixed monophyletic group. Inferred ancestral character states within the Collema-Leptogium complex revealed that the ancestor of this family had a thallus without cortex and that a cortex evolved at least twice relatively early in the evolution of the Collemataceae s. str. These independent gains of a thallus cortex seems to be associated with a transition from colonizing bare rocks and soils in semi-arid and exposed habitats to epiphytism in shady humid forests.

• character evolution
• classification
• Collema
• Collemataceae
• Leptogium
• lichens
• mtSSU
• nrLSU
• phylogeny
• Physma
• Staurolemma

We thank the curators of ASU, MA, G, CBG, COL, DUKE for loan of specimens. We also thank R. Torices for his help with phylogenetic methods. MGO thanks the National Science Foundation for it financial support of her visit to the Lutzoni lab at Duke University as part of the Assembling the Fungal Tree of Life (AFTOL) project (DEB-0228668). Finally we thank two anonymous reviewers for critically reading the manuscript. This study also was supported by a predoctoral fellowship from Rey Juan Carlos University to MGO and by the Spanish Ministry of Education (project CGL 2004-04795-CO4-04).