Systematics/Phytogeography / Taxonomie/ Section
Kennedy, Aaron H. , Watson, Linda E. .
Phylogenetic relationships within the myco-heterotrophic Hexalectris Raf. (Orchidaceae).
Myco-heterotrophic plants (MHPs) sequester photosynthetic carbon via an association with mycorrhizal fungi. Plants with these characteristics have evolved independently in many distantly related angiosperm families including the Burmanniaceae, Corsiaceae, Gentianaceae, Geosiridaceae, Lacandoniaceae, Monotropaceae, Orchidaceae, Petrosaviaceae, Polygalaceae, and Triuridaceae. Yet despite this frequency, and the historical fascination that botanists and mycologists alike have had with MHPs, very few studies have examined species-level patterns of evolutionary relationships within lineages that contain these plants. This paucity of phylogenetic studies has been attributed to i) a scarcity of study material due to the cryptic and ephemeral nature of MHP’s aboveground organs and their occurrence in inaccessible habitats and, ii) high substitution rates in plastid genomes, which has lead to PCR and sequencing difficulties. The eight myco-heterotrophic species that comprise Hexalectris Raf. (Orchidaceae) are rarely detected and collected throughout their mostly southwestern US and Mexican distributions. Phylogenetic analyses of DNA sequence data from six plastid regions and the ITS support most species’ circumscriptions with the exception of two. There is well-supported topological incongruence between plastid and ITS trees, which suggests that hybridization may have played a role in the diversification of Hexalectris. In addition, relative rate tests for two plastid regions and the ITS estimate higher rates of sequence evolution in Hexalectris compared to close autotrophic/photosynthetic relatives.
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1 - Miami University, Department of Botany, Oxford, Ohio, 45056, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 2:30 PM