Insights into the evolution of the tribe Arctoteae (Compositae: subfamily Cichorioideae s.s.) using trnL-F, ndhF, and ITS
Abstract:Compositae (Asteraceae) are the largest flowering plant family (23,000 to 30,000 species) and its members are found throughout the world in both temperate and tropical habitats. The subfamilies and tribes of Compositae remained relatively constant for many years; recent molecular studies, however, have identified new subfamilial groups and identified previously unknown relationships. Currently there are 35 tribes and 10 subfamilies (Baldwin & al., 2002; Panero & Funk, 2002). Some of the tribes and subfamilies have not been tested for monophyly and without a clear understanding of the major genera that form each tribe and subfamily, an accurate phylogeny for the family cannot be reconstructed. The tribe Arctoteae (African daisies) is a diverse and interesting group with a primarily southern African distribution (ca. 17 genera, 220 species). They are especially important in that most of the species are found in the Cape Floral Kingdom, the smallest floral kingdom and the subject of intense conservation interest. Arctoteae are part of the monophyletic subfamily Cichorioideae s.s. Other tribes in the subfamily include Eremothamneae, Gundelieae, Lactuceae, Liabeae, Moquineae, and Vernonieae, and these were all evaluated as potential outgroups. Ultimately 29 ingroup taxa and 16 outgroup taxa with a total of 130 sequences (125 newly reported), from three genetic regions, two from chloroplast DNA (trnL-F and ndhF) and one from the nuclear genome (ITS), were used to evaluate the tribe and its proposed outgroups. Each molecular region is examined separately, the chloroplast markers are examined together, and the data are combined. The data were analyzed with and without outgroups and problem taxa using parsimony and maximum likelihood methods. The analyses showed robust support for two outgroup clades, Liabeae-Vernonieae and Gundelieae-Lactuceae and two main subtribes within Arctoteae: Arctotineae and Gorteriinae. Support for monophyly of Arctoteae is weak. Within Arctoteae, some taxa of interest are easily placed: Didelta, Cuspidia and Heterorhachis are consistently part of subtribe Gorteriinae, Cymbonotus, the Australian genus, is nested within subtribe Arctotineae, and Haplocarpha is at the base of Arctotineae. Berkheya, Haplocarpha, and Hirpicium are probably paraphyletic. Furthermore, Platycarpha most likely does not belong in Arctoteae, and Heterolepis and the tribe Eremothamneae are within Arctoteae but not within either of the two main subtribes. After some rearrangements, the two main subtribes, Arctotineae and Gorteriinae, are monophyletic and the latter has three clades. The study shows that the unusual taxa are of critical importance, and they should be included in any molecular analysis. Adequate representation of the ingroup is also important as all previous studies of Arctoteae had involved only a few taxa from the core subtribes, and so did not reveal the problems. Multiple outgroups evaluated in an iterative manner had pronounced effects on the relationships within the ingroup, not only on the position of the root. Finally, unrooted consensus trees and unrooted phylograms were found to be very useful in analyzing the data, allowing for examination of placement of taxa without the bias of a rooted tree.
Document Type: Research Article
Publication date: August 1, 2004
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