Date of Award:

5-1-1990

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Mary E. Barkworth

Committee

Mary E. Barkworth

Committee

Kay Asay

Committee

Chris Chapman

Committee

James MacMahon

Committee

Richard Mueller

Abstract

Thinopyrum sensu Dewey is a genomically defined genus of the perennial Triticeae consisting of sect. Thinopyrum, originally based on the J genome, sect. Lophopyrum, originally based on the E genome, and sect. Trichophorae, based on an EES genome constitution. The relationships among its taxa are complex. This has led to a variety of classifications being proposed, based primarily on morphological or genomic data. The major cause of disagreement between the two types of classification is the genomic similarity but morphological dissimilarity between sect. Thinopyrum and sect. Lophopyrum. The goal of my research was to clarify the relationships within Thinopyrum sensu Dewey using data from morphology, anatomy, isozyme variation and field studies. The data obtained, in combination with cytogenetic data, suggest that the E and J genome groups are morphologically distinct as a result of rapid morphological adaptation by sect. Thinopyrum in response to its xeric habitat, along shorelines. The high genomic and isozymic similarity between the sections indicate that this rapid morphological change was not accompanied by major genetic change. These support the inclusion of the two sections in the same genus. Thinopyrum sect. Trichophorae was found to be very similar in terms of its morphology to T. sect. Lophopyrum. As a result of morphological and genetic similarity the two sections should be placed in a common section. Examination of the data obtained in this study, in combination with accounts of natural hybrids and published cytogenetic data, indicate that the two sections are best treated as cohgeneric with Elytrigia sect. Elytrigia. The taxa of Thinopyrum sect. Lophopyrum and Trichophorae should be placed together in Elytrigia sect. Caespitosae. Thinopyrum sect. Thinopyrum should be placed in Elytrigia as a distinct section, E. sect. Junceae.

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