Achillea millefolium agg. is an ecologically most diverse N Hemisphere polyploid complex. Because of ubiquitous hybridization and polyploidization, the aggregate is extremely polymorphic and notorious for its difficult taxonomy. AFLP analyses were applied to 61 populations representing most of the known taxa of A. millefolium agg. Genetic distance methods of population pairwise FST and Neighbour Joining for tree constructions and the 2D_Euklid algorithm for scatter plots were used to evaluate the AFLP-matrix with 459, mostly polymorphic bands. The aggregate is monophyletic and sister to the subalpine relic A. latiloba-2x from NE Turkish and adjacent Georgian mountains. The seven 2x-species of A. millefolium agg. have differentiated vicariously in Europe/SW Asia and expanded into C and E Asia. Both, the NJ trees and the 2D_Euklid scatterplots demonstrate these 2x as genetically monophyletic and distinct; only A. roseoalba-2x, close to A. asplenifolia-2x, may be the product of hybrid introgression. The polyploids of the aggregate (about 20 taxa and cytotypes) exhibit various combinations of 2x AFLP bands, but in addition also 16.9% of exclusive bands, documenting new genetic variation. Whereas the ALFP trees suggest most of these polyploid taxa to be polyphyletic, the AFLP 2D_Euklid scatterplots demonstrate their phyletic coherence. This conflicting evidence apparently is due to wide-spread secondary hybrid merging between sympatric populations of different polyploid taxa, resulting in geographic instead of phyletic clustering of their populations in the AFLP trees. Available data suggest several parallel reticulating and ascending polyploid lines and their eco-geographical radiations. This has resulted in the origin of eight taxa of 4x, four or five of 6x and three of 8x in Europe and the Caucasus. One of them, A. millefolium subsp. millefolium-6x, also occurs throughout Asia, where two more 4x taxa, one additional 6x and one 8x can be recognized. Finally, from ancestors close to A. asiatica s.str.-4x, the A. borealis s.l. clade has originated in N America, where it has radiated with numerous 4x- and 6x-ecotypes into most diverse habitats. Thus, the polyploid complex A. millefolium agg., shaped by successive cycles of differentiation and hybridization + polyplodization, has expanded stepwise from Europe and SW Asia to E Asia, then to N America and finally world-wide with A. millefolium-6x as a weed.
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ACHILLEA MILLEFOLIUM AGG;
MDS (MULTIDIMENSIONAL SCALING);
Document Type: Research Article
Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, and College of Life Sciences, Beijing Normal University, Beijing 100875, China
Department of Pharmacognosy, University of Vienna, Althanstraße 14, 1090 Vienna, Austria
Department of Systematic and Evolutionary Botany, Faculty of Life Sciences, University of Vienna, Rennweg 14, 1030 Vienna, Austria
Publication date: 2008-02-01
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