Doctoral Dissertations

Date of Award

12-1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Botany

Major Professor

Ronald H. Petersen

Committee Members

K. W. Hughes, E. E. Schilling, J. L. Gittleman

Abstract

This study investigated the systematic relationships within a small section of the genus Xeromphalina utilizing morphological characters, mating systems, mating compatibility, and sequences of the internal transcribed spacers of the nrDNA

This study had the following goals: 1) to evaluate previous taxonomies, 2) evaluate previously utilized and new morphological characters for use in systematic studies; 3) trough ancestral character state reconstruction characters draw inferences about morphological evolution; 4) determine the mating system operating in as many taxa as possible to evaluate the potential use of mating systems as a taxonomic character for the genus, 5) determine the number of intersterility groups, 6) determine the phylogenetic relationships within the genus utilizing ITS sequences; and 7) compare different data sets to determine the appropriateness of different species concepts for the group.

Morphological analyses (phenetic and cladistic) showed that morphological variation in this group was limited and most variable characters were homoplasious, but unique character state combinations were detected that allow identification of all groups identified by other methods.

Mating systems for 12 taxa were determined to be tetrapolar despite previous reports of a bipolar mating system in X. campanella. These results indicate that mating system is not a useful taxonomic character in this genus.

Compatibility data supported recognition of X. brunneola and X. kauffmanii, revealed the presence of two intersterility groups within the traditional limits of X. campanella, and identified two additional intersterility groups represented by single collections. These intersterility groups corresponded to morphologically identifiable groups.

Phylogenetic relationships within the genus and a whole and within the X, campanella complex were discussed. The intersterility groups identified in compatibility studies were monophyletic except for the two single collection groups, which form paraphyletic groups within other clades.

Based on these data (morphology, compatibility, and molecular), a pluralistic species concept was advocated. And under this species concept four species would be recognized, X. brunneola, X. campanella group I, X. campanella group II, and X. kauffmanii. Because of nomenclature problems with X. campanella, names for the two taxa cannot yet be proposed. Taxonomic status of the single collection intersterility groups was unresolved.

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