The ITS data provide weak support for the monophyly of Subtribe Artemisiinae (Fig. 1), i.e., 67% posterior probability as estimated by MrBayes and unsupported as measured by parsimony bootstrap analysis (<50%). ndhF sequence data also failed to resolve or support the monophyly of Subtribe Artemisiinae 64. In the ITS phylogeny, only one genus appears to disrupt its monophyly, Stilnolepis, which occupies the basal-most position of the ingroup. However, the next node up is supported at a 94% posterior probability, indicating that Subtribe Artemisiinae is likely monophyletic, with the possible exception of Stilnolepis.

The ITS phylogeny (Fig. 1) resolved three major clades within Subtribe Artemisiinae that correspond to the following: 1) all subgenera of Artemisia minus Dracunculus, 2) Artemisia subg. Dracunculus, and 3) the largely radiate members of the subtribe (Ajania, Arctanthemum, and Dendranthema). All three clades have segregate genera embedded within each (indicated in bold), and these clades are supported at 77, 74, and 99% posterior probabilities, respectively, with the third clade also supported by a bootstrap value of 99%. The Artemisia-group sensu Bremer and Humphries 2 is not monophyletic because three segregate genera Elachanthemum, Stilnolepis, and Kaschgaria are excluded from this clade. Additionally, Artemisia s.l. is monophyletic only with the inclusion of five segregate genera: Seriphidium, Sphaeromeria, Neopallasia, Crossostephium, and Filifolium. Additionally, this clade is only weakly supported with a 63% posterior probability and bootstrap support <50%.

Three of the eight segregate and allied genera that we examined were placed outside of the Artemisia-group (including Stilnolepis, Elachanthemum, and Kaschgaria), whereas the remaining five were placed within it (including Seriphidium, Sphaeromeria, Neopallasia, Crossostephium, and Filifolium). However many of these placements are among the most weakly supported branches of the resulting phylogenetic trees (Fig. 1).

Stilnolepis, Elachanthemum, and Kaschgaria are excluded from the clade of the Artemisia-group, and are, in part, sister to all remaining Artemisiinae genera in the ITS phylogeny. Stilnolepis and Elachanthemum are monotypic genera that occur in Central Asia, that are often treated as a single genus, Stilnolepis 2. However, our ITS phylogeny supports Ling's treatment of them as two distinct genera 54. Neither genus appears to be a member of Artemisia s.l. or the Artemisia-group. Both genera are discoid with corymbose capitula, but whether either genus possesses spineless pollen (a synapomorphy for the Artemisia-group) or is wind-pollinated has not yet been determined 237. Kaschgaria, a genus of two species from China and central Asia, is also placed outside of the Artemisia-group, but clearly within Subtribe Artemisiinae (94% probability) in the ITS phylogeny. Kaschgaria was removed by Poljakov from Artemisia s.l. on the basis of stellate corolla hairs, and was considered more closely related to Seriphidium than Artemisia s.s., even though it is disciform rather than discoid 2. Kaschgaria possesses spineless pollen 237. Therefore, placement of Kaschgaria and Elachanthemum outside of the Artemisia-group is intriguing because if these placements remain robust, wind-pollination may have arisen more than once in the tribe, or insect-pollination may be secondarily derived within Subtribe Artemisiinae in the radiate genera (clade 3 of Fig. 1).

Four of the small allied/segregate genera are embedded within the clade of the Artemisia-group, in addition to the large segregate genus Seriphidium (Fig. 1). Filifolium is sister to species of subg. Dracunculus, and together comprise a sister clade to all remaining Artemisia species and four segregate genera, moderately supported at 74% probability. Monotypic Filifolium occurs in China and Korea, and was previously considered a species of subg. Dracunculus on the basis of sterile disk florets. Cassini 65 segregated subg. Dracunculus as Oligosporus with the sterility of the central florets as the defining synapomorphy that unites these species (Fig. 2b). Bremer and Humphries 2 noted that Mausolea and Picrothamnus share this trait, and suggested that Oligosporus should be resurrected and defined to include these three segregate genera. Mausolea was segregated by Poljakov 38 from Artemisia s.l. by marginal flowers that lack corollas. Picrothamnus was established by Nuttall, but reduced as A. spinescens Hall and Clements, and according to Bremer and Humphries 2 is essentially Dracunculus with two autapomorphies: spiny habit and cobwebby-pilose cypselas. Thus two taxonomic treatments are viable: 1) the recognition of two subgenera within Artemisia s.l. – subg. Dracunculus and an expanded subg. Artemisia; or 2) the resurrection of Oligosporus (following Cassini) to include species of subg. Dracunculus, Filifolium, and perhaps Mausolea and Picrothamnus. Unfortunately we were unable to obtain ITS sequences for Mausolea or Picrothamnus.

Monotypic Crossostephium was treated as a segregate genus of Artemisia by Bremer and Humphries 2. It is distinct from Artemisia by the presence of a coroniform pappus, however it was once placed near A. californica by Gray 45 and Rydberg 47 on the basis of deeply-ribbed cypselas. Crossostephium occurs in the Phillipines, Taiwan, southern Japan, and China, whereas A. californica occurs in western North America. Based on the ITS results, we conclude that Crossostephium is allied with Old World Seriphidium and several Artemisia subg. Artemisia species, and A. californica is sister to most of the New World species of Seriphidium (Fig. 1). Although placements of both are weakly supported (68 and 57% probabilities for Crossostephium and A. californica, respectively; Fig 1).

Neopallasia is a genus of three species that occur in central Asia, including southern Siberia, Mongolia, and China 2. It was segregated from Artemisia by Poljakov 66 on the basis of several autapomorphies, including pectinate leaves, central-sterile florets at the apex of the capitulum, ovoid-lanceolate anther appendages, and a rosette-shaped arrangement of cypselas on the receptacle. Poljakov 66 and Bremer and Humphries 2 contended that Neopallasia is closely related to Artemisia subg. Drancunculus. However, the ITS data place Neopallasia sister to Asian species of Seriphidium and some members of Artemisia subg. Artemisia, close to Crossostephium. This placement is moderately supported at 87% probability.

Sphaeromeria is considered closely related to Artemisia s.l., although it was once treated as a section of Tanacetum 55. It is a small genus of nine western North American species, and has no autapomorphies that distinguish it from Artemisia s.l. Bremer and Humphries 2 suggested that it might be more closely related to Kaschgaria, a genus composed of two species that occur in central Asia and China. They are similar in habit and have similar inflorescences that are slightly elongated. However, in the ITS phylogeny (Fig. 1), Sphaeromeria is distant to Kaschgaria. Rather its placement is unsupported within a Seriphidium subclade that contains several anomalous North American species, some of which have been placed in sect. Tridentatae. However, because of the lack of support for placement of Sphaeromeria, we are hesitant to suggest that it be submerged in Artemisia s.l. without further study. However, it does not appear closely related to Kaschgaria.

Seriphidium palmeri is an anomalous species that was once treated as segregate genus Artemisiastrum. The ITS phylogeny places it among New World subg. Artemisia species, in agreement with previous studies 3435 and not in agreement with Bremer and Humphries 2 who place it near Seriphidium sect. Tridentatae. This is a strongly supported relationship at 100% bootstrap and 99% probability. Thus Artemisiatrum, should not be resurrected, with S. palmeri more closely related to the New World species of Artemisia subg. Artemisia rather than with the New World Seriphidium species that comprise sect. Tridentatae.

While this study is incomplete with regards to subgeneric boundaries because only a limited number of Artemisia species was sampled from this large genus, some preliminary conclusions can still be made on emerging patterns of the derived phylogeny. Artemisia subg. Artemisia is not supported as monophyletic, with its species placed in six different clades in the ITS tree (Fig. 1). It is apparently defined taxonomically on the basis of plesiomorphies (heterogamous, disciform capitula with perfect/fertile disk florets and pistillate ray florets), and needs to be re-circumscribed. Artemisia subg. Absinthium is monophyletic (96% probability, 76% bootstrap) in the ITS phylogeny and differs from all other subgenera by a hairy receptacle. However it is embedded within a clade of species of Old World subg. Artemisia. Thus, we agree with Gray 45 that the species of subg. Absinthium should be merged into subg. Artemisia. Similarly, Old World Seriphidium species are monophyletic (96% probability), but should also be subsumed within Artemisia subg. Artemisia.

Previously, the origin of the Tridentatae was unresolved with competing hypotheses from the New World Artemisia species vs. Old World Seriphidium species being equivocal 3435. The current ITS phylogeny suggests that the closest relatives of Tridentatae lie among the New World species of Artemisia, in agreement with McArthur and Plummer 20, perhaps sharing a common ancestry with A. filifolia and A. californica, in addition to Sphaeromeria, although monophyly for this subclade is unsupported by the ITS data. Seriphidium sect. Tridentatae does not share a most recent common ancestor with Old World Seriphidium species, and it should not be treated with the Old World woody artemisias, as we and others have previously suggested 343536.

Seriphidium sect. Tridentatae is characterized by discoid-homogamous capitula, with the exception of S. bigelowii, which has occasional heterogamous-disciform capitula of one pistillate ray floret and two perfect disk florets – a character that was previously considered a plesiomorphy or secondary reversal in S. bigelowii 2. Based on ITS and chloroplast phylogenies of sect. Tridentatae, we previously concluded 3435 that S. bigelowii was perhaps misplaced and should be excluded from the Tridentatae. In addition, we explained 3435 an unexpected relationship between it and A. filfifolia as possible hybridization and introgression involving bidirectional gene flow rather than recent common ancestry because heterogamous-disciform A. bigelowii differs from heterogamous-disciform A. filifolia by perfect disk florets instead of female-sterile disk florets. Sphaeromeria also has heterogamous-disciform capitula with pistillate ray and perfect disk florets, as does heterogamous-disciform S. bigelowii, suggesting that it is indeed a plesiomorphy. The occasional appearance of disciform capitula in S. bigelowii might be explained by introgression of genes or alleles from A. filfolia that control ray expression, a phenomenon observed in discoid Senecio squallidus and radiate S. vulgaris in Europe 67. While this is speculative, it is consistent with hypotheses that hybridization and introgression are widespread in sect. Tridentatae 68, and may explain occasional heterogamous disciform capitula in S. bigelowii 3435. However, there may be many genetic and developmental mechanisms that affect ray formation and control floret fertility 6970.

Artemisia subg. Drancunculus is monophyletic and is sister to all remaining Artemisia species. It, perhaps combined with Filifolium, Mausolea, and Picrothamnus, could be treated as a separate genus, Oligosporus (following Cassini), or as one of two subgenera of Artemisia. In the latter case, all remaining species of Artemisia (including subg. Absinthium and Artemisia) and Seriphidium (including sect. Tridentatae) would collectively form a much expanded subg. Artemisia. Thus, Artemisia s.l. should either be treated as two subgenera, i.e., a largely expanded subg. Artemisia (Clade 1 of Fig. 1) and Dracunculus (Clade 2 of Fig. 1), or as two distinct genera, Artemisia and Oligosporus. Both clades are moderately supported at 77 and 74% probabilities, and include several segregate genera as well. Therefore, we favor retaining the Linnean concept of the genus with subg. Dracunculus conserved, and the numerous segregate genera eventually being subsumed within Artemisia s.l.

Sister group relationships of Subtribe Artemisiinae were unresolved on the basis of morphology 2. However an ITS phylogeny of Francisco-Ortega et al. 62 that primarily focused on the origin of Macaronesian endemic genera of Anthemideae revealed a possible sister group relationship of Leucanthemella and Nipponanthemum (Subtribe Leucantheminae) to Subtribe Artemisiinae. Monotypic Nipponanthemum occurs in Japan and the two species of Leucanthemella occur in Eastern Europe and the Far East in Manchuria, Korea, and Japan. An ITS phylogeny of Subtribe Leucantheminae 71 also excluded these two genera from that subtribe, which is otherwise Mediterranean in distribution, congruent with a chloroplast phylogeny based on ndhF for the entire tribe 64. The ndhF phylogeny failed to support the subtribal classification of Tribe Anthemideae sensu Bremer and Humphries, and failed to resolve the intergeneric relationships or support the monophyly of Subtribe Artemisiinae. However this study resulted in the recognition of the importance of biogeography in the evolution of the tribe as a whole, with a major divergence between relictual South African genera and Northern Hemisphere Eurasian genera where members of Subtribe Artemisiinae were placed. Our ITS phylogeny of Subtribe Artemisiinae that included 40 outgroup genera from seven Anthemideae subtribes also supports a sister group relationship of Nipponanthemum and Leucanthemella to Subtribe Artemisiinae (Fig. 1).

A close resemblance of Nipponanthemum and Leucanthemella to the Asian genus Dendranthema of Subtribe Artemisiinae was previously noted by Bremer and Humphries 2, when they provisionally placed these genera in Subtribe Leucantheminae. The ITS data clearly support a sister group relationship between these two genera and subtribe Artemisiinae and their exclusion from Subtribe Leucantheminae. Both Leucanthemella and Nipponanthemum are radiate, supporting a radiate ancestry for Subtribe Artemisiinae.

The genera that comprise the Artemisia-group are closely related and were considered monophyletic on the basis of ancestrally, disciform-heterogamous capitula and spineless pollen, with discoid capitula secondarily derived by the loss of ray or marginal florets (Fig. 2). Phaeostigma and Ajania, which are sister to the Artemisia-group in the Bremer and Humphries 2 cladogram, contain some species that were once classified as Artemisia s.l. since they are also disciform. However, these two genera were removed from Artemisia s.l., and on the basis of spiny pollen have been considered transitional between the Artemisia-group and four radiate genera: Tridactylina Arctanthemum, Brachanthemum, and Dendranthema. Our ITS phylogeny places disciform Ajania sister to radiate Arctanthemum derived from within the Arctanthemum-Dendranthema clade, rather than sister to the Artemisia-group. Thus, disciform Ajania does not appear to be intermediate between radiate Artemisiinae and disciform Artemisia and allies. Furthermore, the tentative placement of disciform Kaschgaria and discoid Stilnolepis sister to the entire subtribe suggests that there may have been multiple origins for disciform, as well as discoid capitula.

A complex scenario for the origin and diversification of Artemisia and Seriphidium, and subsequent parallel evolution of the two genera in the Old and New Worlds, was proposed by Ling 3949. The putative common ancestor to both "sister genera" was hypothesized to have existed in northern Asia, based on reported fossil pollen records that date the taxa to the early Oligocene or lower Eocene of the lower Tertiary, with speciation accompanied by migrations during the Tertiary and Quaternary periods – forced southward by the advancing polar ice sheets. Hypothesized migrations out of northern Asia purportedly occurred along three lines: 1) westward into Europe, with gradual migration into North America, western Asia, Asia Minor, the Mediterranean, and Africa; 2) eastward into Siberia into western North America, and into eastern Europe; and 3) further south into Asia primarily during the Quaternary. Seriphidium is clearly embedded as two distinct clades within Artemisia in the molecular phylogenies, making a sister group relationship unlikely.

According to Ling 3949, a 'pro-Absinthium' ancestor in northern Asia gave rise to members of Absinthium, which directly gave rise to Abrotanum, which subsequently gave rise to Seriphidium. An Absinthium origin for Seriphidium has also been proposed on the basis of flavonoid data 72. The ITS data do not support a sister group relationship of members of subg. Absinthium to the remainder of Artemisia s.l. In contrast, Absinthium is embedded within a derived clade composed of both Old and New World members of subg. Artemisia. A proposed secondary diversification occurred during the Himalayan uplift in the late Tertiary, and resulted in a center of diversity that today harbors 116 species of regional endemics of Artemisia s.s. A more detailed examination of Artemisia s.l. is necessary to more fully evaluate this hypothesis.

Hall and Clements 44 proposed a sister group relationship of subg. Artemisia to remaining subgenera. This hypothesis is also not supported because subg. Artemisia is not monophyletic. In contrast, the ITS phylogeny supports an early divergence of subg. Dracunculus from the remaining Artemisia subgenera.

It appears that the New World species of Artemisia s.l. are paraphyletic and that the North American lineages arose once with at least one back migration to the Old World by some members of subg. Artemisia and Absinthium (Fig. 2). Alternatively, the North American lineages may have arisen twice, independently. Graham 73 suggested that the most convincing earliest fossil pollen records for Artemisia are late Oligocene from Central Europe. In all likelihood, Subtribe Artemisiinae and Artemisia s. l. originated in Eurasia sharing a relatively ancient common ancestry with Asian members of Leucantheminae and South African members of Subtribe Matricariinae 64.