Molecular phylogeny of Subtribe Artemisiinae (Asteraceae), including Artemisia and its allied and segregate genera

Abstract

Background: Subtribe Artemisiinae of Tribe Anthemideae (Asteraceae) is composed of 18 largely Asian genera that include the sagebrushes and mugworts. The subtribe includes the large cosmopolitan, wind-pollinated genus Artemisia, as well as several smaller genera and Seriphidium, that altogether comprise the Artemisia-group. Circumscription and taxonomic boundaries of Artemisia and the placements of these small segregate genera is currently unresolved.

Results: We constructed a molecular phylogeny for the subtribe using the internal transcribed spacers (ITS) of nuclear ribosomal DNA analyzed with parsimony, likelihood, and Bayesian criteria. The resulting tree is comprised of three major clades that correspond to the radiate genera (e.g., Arctanthemum and Dendranthema), and two clades of Artemisia species. All three clades have allied and segregate genera embedded within each.

Conclusions: The data support a broad concept of Artemisia s.l. that includes Neopallasia, Crossostephium, Filifolium, Seriphidium, and Sphaeromeria. However, the phylogeny excludes Elachanthemum, Kaschgaria, and Stilnolepis from the Artemisia-group. Additionally, the monophyly of the four subgenera of Artemisia is also not supported, with the exception of subg. Dracunculus. Homogamous, discoid capitula appear to have arisen in parallel four to seven times, with the loss of ray florets. Thus capitular morphology is not a reliable taxonomic character, which traditionally has been one of the defining characters.

Figure 1

Maximum likelihood tree based on ITS sequence data for Subtribe Artemisiinae (Asteraceae). With the exception of Nipponanthemum, Leucanthemella, Cymbopappus, Pentzia and Oncosiphon, all outgroup genera used in analysis are not shown but are listed in Table 1 (see additional file 1). Small segregate and allied genera of Artemisia s.l. are in bold. Subgeneric assignments for Artemisia s.s. are indicated by colored boxes. All Artemisia species that are not placed in a colored box are members of subg. Artemisia and primarily occur in the Old World. Numbers followed by '%' are bootstrap values derived from 100 bootstrap replicates using parsimony criteria, and numbers followed by 'p' are posterior probabilities derived from Bayesian analysis using likelihood criteria.

Figure 2

Character evolution of Subtribe Artemisiinae (Asteraceae) mapped on to the Maximum Likelihood tree derived from ITS sequence data. Unless otherwise indicated by colored boxes, all Subtribe Artemisiinae species are wind-pollinated, occur primarily in Eurasia, and possess heterogamous-disciform capitula with perfect (bisexual) disk and pistillate ray florets.