Systematics/Phytogeography / Taxonomie/ Section
Rai, Hardeep , Nagalingum, Nathalie , Wu, Yihao , Little, Damon , Stevenson, Dennis Wm. , Mathews, Sarah .
Phylogenetic relationships within and among cycad genera inferred from phytochrome genes.
Cycads are the oldest crown group of seed plants and are represented by approximately 300 living species. Relationships among genera of the cycads (Cycadales) remain ambiguous, primarily due to disagreements regarding the relative placement of a few genera along the backbone of the tree. However, previous analyses of both molecular and morphological data have provided evidence that Cycas is sister to all other cycads, and have consistently united Zamia with Microcycas. To gain further insight into relationships within and among cycad genera, we are accumulating phytochrome data from a nearly comprehensive sampling of the order (currently we have sampled 72 species). Preliminary analyses of partial sequences from PHYN and PHYP (a combined total of 4202 nucleotides, including PHYP intron 1) strongly support 1) the position of Cycas as the sister to the remaining cycads, 2) a clade of Lepidozamia plus Encephalartos, with Macrozamia as their sister, 3) a clade in which Zamia + Microcycas and Stangeria + Ceratozamia are sister clades, with Bowenia as their sister, and 4) a clade of Dioon. The strong support for these clades and their components significantly advances our understanding of phylogenetic relationships within Cycadales based on analyses of molecular data. The positions of Lepidozamia, Encephalartos, Macrozamia, and Ceratozamia are consistent with trees from previous analyses of morphological data, and with some, but not all, published molecular trees. Previous analyses of molecular data also suggested that Stangeriaceae is not monophyletic, but they failed to place the component genera (Bowenia and Stangeria). In some cases, relationships within genera also are supported by the phytochrome data and we expect that the addition of data from PHYO may provide further insight at these levels, and into the relative positions of Dioon and the other two clades that diverge above Cycas.
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1 - Harvard University, Arnold Arboretum, 22 Divinity Avenue, Cambridge, MA, 02138, United States
2 - The New York Botanical Garden, 200th Street & Southern Blvd., Bronx, NY, 10458, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Room 6/Woodward
Date: Tuesday, July 29th, 2008
Time: 10:00 AM