Systematics/Phytogeography / Taxonomie/ Section
Dueck, Lucy A. , Cameron, Kenneth M. .
Interspecific relationships and a new species of Spiranthes, the ladies'-tresses orchids.
A four-gene hypothesis of phylogenetic relationships among more than 200 samples of Spiranthes was conducted using combined nuclear and plastid DNA sequences from ITS, matK, trnS-G-fm and the trnL intron. Nearly all species native to North America, Europe, and Asia were included in the analyses; only a handful of species were unavailable for study. The cladogram based on combined data is generally well resolved, and most relationships receive high jackknife support values. All Old World endemic species form a monophyletic clade embedded within the tree, indicating their likely origin from a New World ancestor. The data fail to discriminate fully the various taxa that comprise the autumn flowering S. cernua complex, and even indicate that some taxa belonging to this group (e.g., S. parksii) may not warrant species status. Conversely, these molecular data have been useful in identifying at least one new species, S. stellata, which was described earlier this year from the northwestern United States. In general, flowering time and chromosome number correlate well with the phylogenetic pattern (e.g., S. praecox, S. porrifolia, S. romanzoffiana, and S. lucida all with a karyotype based on n=22 are sister to the remainder of the genus based on n=15). However, the common occurrence of allopolyploids within Spiranthes presents a challenge to understanding its complete evolutionary history. Further studies, especially at the population level, will be essential for better understanding these temperate orchids.
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1 - Savannah River Ecology Laboratory (formerly), Aiken, SC, 29802, USA
2 - University of Wisconsin, Madison, Herbarium and Department of Botany, Birge Hall, 430 Lincoln Dr., Madison, WI, 53706, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 2:45 PM