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Journal Article

nrDNA External Transcribed Spacer (ETS) Sequence Data, Reticulate Evolution, and the Systematics of Machaeranthera (Asteraceae)

David R. Morgan
Systematic Botany
Vol. 28, No. 1 (Jan. - Mar., 2003), pp. 179-190
Stable URL: http://www.jstor.org/stable/3093947
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
nrDNA External Transcribed Spacer (ETS) Sequence Data, Reticulate Evolution, and the Systematics of Machaeranthera (Asteraceae)
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Abstract

Sequence data from the nrDNA external transcribed spacer (ETS) were generated to help resolve questions about the evolution of Machaeranthera left unanswered by previous analyses of chloroplast DNA (cpDNA) restriction site data and nrDNA ITS sequence data. Combined ITS and ETS (nrDNA) evidence agreed with cpDNA evidence in supporting a close relationship between Oönopsis and M. tanacetifolia. Nuclear rDNA evidence also supported an alliance between M. sections Blepharodon and Sideranthus. The nrDNA evidence provided greater support for the relationships of M. gypsitherma, M. heterophylla, M. stenoloba, and M. viscida than earlier analyses of ITS sequence data, reinforcing earlier conclusions that these species have experienced reticulate evolution. Finally, nrDNA evidence provided strong support for a group consisting of M. bigelovii, M. canescens, M. gypsitherma, and M. riparia. The relationships that nrDNA evidence supported for these four species conflicted substantially with those supported by cpDNA evidence. The many instances of conflict between cpDNA and nrDNA suggest that the evolution of Machaeranthera has been complex and may have involved as many as seven separate occurrences of reticulate evolution.

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