• Achillea, a temperate genus of herbaceous allogamous perennials, is a model for evolutionary radiation through hybridization and polyploidization. • AFLP analyses were performed on 300 individuals ...of 66 populations and 27 taxa/cytotypes, mainly from the polyploid A. millefolium aggregate and its suspected hybrid links with other clades of the genus. • The mosaic genetic structure of hybrids and polyploids is revealed by specific AFLP bands shared with their assumed parents. In E Asia, A. alpina-4x and A. wilsoniana-4x are allotetraploids between A. acuminata-2x (sect. Ptarmica) and A. asiatica-2x (sect. Achillea-A. millefolium agg.). A. virescens-4x is a hybrid species linking A. nobilis agg. and A. millefolium agg. in S Europe. The hybrid swarm A. clypeolata-2x × A. collina-4x recently formed in Bulgaria shows no AFLP bands additive to its parents; by contrast, other more ancient allopolyploids exhibit genetic innovations. Relationships within A. millefolium agg. are complex. Five 2x-taxa, mostly well separated and regressive, are limited to Eurasia; seven 4x- and 6x-taxa are intimately linked by hybridization, are expansive, and through A. asiatica-2x/4x have formed the N American polyploids. • All these results from AFLPs correspond well to other evidence, and indicate a long history of reticulate evolution in Achillea.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
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 ${\rm F}_{{\rm ST}}$ 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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Successful crossing experiments between the tetraploids Achillea ceretanica4x, A. collina, A. distans subsp. styriaca, A. pratensis, and the octoploid A. monticola, all from the A. millefolium agg. ...(Compositae), are reported. Chromosomes were studied in 514 out of 883 hybrid plants obtained from 13 crossings. F
i
-offspring from tetraploid parents was generally tetraploid, but some combinations produced up to 30% of aneuploid, near-pentaploid, and even hexaploid F
1
-individuals. A backcross and a F
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-progeny consisted of normal tetraploids. A reciprocal F
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-combination involving a tetraploid parent with one B-chromosome showed an increase of B-chromosomes in the F
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, when the male transmitted the B (69.2%), and a decrease, when the female had the B (33.3%). Mainly hexaploid offspring resulted from a reciprocal F
1
-cross between tetraploid and octoploid parents.
New crossing and selfing experiments within Achillea millefolium agg. (Compositae) succeeded with tetraploid individuals of A. ceretanica -4 x, A. collina, A. pratensis and F
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hybrids. Chromosome ...numbers of 105 out of 785 individuals including F
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, BC, S
1
offsprings and free pollinated F
1
progenies were studied. Generally, plants were tetraploid, but occasionally aneuploids and a near-pentaploid plant originated from crossing and selfing experiments with A. ceretanica-4x and A. collina. The high degree of selfincompatibility within Achillea millefolium agg. is confirmed.
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