Phylogeny and systematics ofAchillea(Asteraceae­Anthemideae) inferred from nrITS and plastidtrnL­FDNA sequences

The N Hemisphere genus Achillea includes about 130 perennial and allogamous species, is centered in SE Europe/SW Asia, and exhibits a complex phyletic structure due to excessive hybridization and polyploidy. About half ofthe species and five of the six traditional sections together with several outgroup genera were studied using nrITS and plastid trnL-F DNA sequences. In spite of some discordance, these markers were shown by Maximum Parsimony and Bayesian Inference to be suitable for revealing relationships with generic allies and for distinguishing the main lineages within Achillea. With the inclusion of Otanthus (and possibly Leucocyclus) Achillea s.1. becomes monophyletic and appears as sister to Anacyclus. A basal clade is formed by the xerophytes of Achillea sections Babounya and Santolinoideae in SW Asia together with the Mediterranean coastal Otanthus. Achillea sect. Ptarmica s.l. has to be divided into the meso- to hygrophytic herbs of A. sect. Ptarmica s.s. in the N Hemisphere and the mountain species of A. sect. Anthemoideae. The latter differentiated in the mountains from NW Anatolia to the Pyrenees, possibly originating from ancestors related to the extant A. ligustica. Finally, taxa of sect. Achillea s.l. (to be merged with A. sect. Filipendulinae) radiated from a center in SE Europe, occupied very different open habitats, and reached an extensive distribution with the very polymorphic polyploid and reticulate complex A. millefolium agg. Here and in other groups of Achillea, various instances of conflicting evidence from nrITS, plastid trnL-F, and morphology point to hybridization and lineage sorting. This means that reticulate evolution is not only involved in recent radiations but must have been active already in the early diversification of the genus.