Hypochaeris

Zidorn, Neela Enke Birgit Gemeinholzer Christian, 2012, Molecular and phytochemical systematics of the subtribe Hypochaeridinae (Asteraceae, Cichorieae), Organisms Diversity & Evolution (New York, N. Y.) 12 (1), pp. 1-16 : 10-13

Hypochaeris

Analysis of the nuclear marker ITS did not provide strong support for or against the monophyly of the genus Hypochaeris ( Figs. 1 , 2 ). Members of Hypochaeris clustered in two clades H I [ Figs. 1 , 2 ; including H. maculata (L.) Bernh., the designated type species of a putative segregate genus Trommsdorffia Bernh. ] and H II ( Figs. 1 , 2 ; including the Hypochaeris type species Hypochaeris radicata L.). Both clades H I and H II are supported by nuclear and plastid markers ( Cerbah et al. 1998, Samuel et al. 2003). This holds true also for the bifurcation that separated the two groups in the study by Samuel et al. (2003). The nuclear ITS data and the combined phylogeny of ITS and the plastid markers trnL and matK supported the monophyly of Hypochaeris in the study of Samuel et al. (2003). An individual assessment of each plastid marker suggests the following conclusions: matK ( Samuel et al. 2003) did not resolve the relationship between Hypochaeris clades H I, H II, and Scorzoneroides .; the trnL intron and the trnL / trnF spacer region ( Samuel et al. 2003) supported two independent genera Trommsdorffia and Hypochaeris congruent with clades Hypochaeris H I and H II, respectively.

Interestingly, an investigation on the geographical origin of Hypochaeris by Tremetsberger et al. (2005) based on ITS sequences, which included only one Leontodon species ( L. saxatilis ), did not support the monophyly of Hypochaeris s. l. Trommsdorffia was also treated as a separate genus by Tzevelev and Fedorov (2003).

Hypochaeris clade H I comprises the South American species of Hypochaeris section Achyrophorus as well as the European and Asian species of the Hypochaeris sections Achyrophorus and Metabasis . This is corroborated by the findings of Samuel et al. (2003). So far, only species with x 0 4 have been reported for the South American members of H I ( Fig. 1 ; see also Weiss et al. 2003, Weiss-Schneeweiss et al. 2003). For the subclade of clade H I, which encompasses the old world members of clade H I, chromosome numbers x 0 3 and x 0 5 have been reported ( Fig. 1 ).

Hypochaeris clade H II includes the old world Hypochaeris sections Hypochaeris and Seriola . These sections feature a pappus of two rows of hairs, whereas the other European sections Achyrophorus and Metabasis feature either one row of hairs or fimbricate scales. The basic chromosome numbers reported are x 0 4, x 0 5, and x 0 6 ( Fig. 1 ).

Whether the genus Hypochaeris is monophyletic or not should be the subject of further molecular and morphological analyses with an extensive taxon sampling before any taxonomic conclusions should be drawn.

Remaining taxa

The exact position of Robertia taraxacoides (synonym: Hypochaeris robertia ) within the Hypochaeridinae remains uncertain; nonetheless, the results presented here suggest reinstating the monotypic genus Robertia DC. instead of merging Robertia with Hypochaeris (synonym: Hypochaeris robertia ). This was also suggested by Siljak-Yakovlev et al. (1994) based on cytogenetic studies.

In contrast to Hypochaeris and Leontodon s.l., the genera Helminthotheca , Picris , Prenanthes and Urospermum can be maintained in their current circumscription. Picris and Helminthotheca , in particular, are monophyletic and share a basic chromosome number x 0 5 ( Fig. 1 ).

Phytochemical analysis

As discussed in some detail elsewhere ( Zidorn 2008b), a major problem with the application of literature data to the phytochemical characterization of taxa is the diverging degree of coverage and the varying quality of the phytochemical data in the literature. This problem is also present in the Hypochaeridinae . However, many of the published data in the Hypochaeridinae are derived from one of the authors of this study (C.Z.) and thus were produced using analytical procedures comparable to those used to generate the new phytochemical data here, in particular data on phenolic compounds contained in some species of the Hypochaeridinae .

Caffeic acid derivatives

The Cichorieae are generally a rich source of caffeic acid derivatives. However, while some compounds, such as chlorogenic acid and 3,5-dicaffeoylquinic acid, are virtually ubiquitous, others, such as as caffeoyltartaric acid and cichoric acid, have a more restricted distribution. In two extensive studies of the genera Crepis and Hieracium , respectively, caffeoyl tartaric acid and cichoric acid were found in nearly all investigated taxa of Crepis but in none of Hieracium ( Zidorn et al. 2002, 2008). Thus, in the present account, we investigated whether caffeic acid derivatives might also serve in the Hypochaeridinae as chemosystematic markers to either characterize the group as a whole or to distinguish between sub-groups within the Hypochaeridinae . As is evident from Table 4, the currently known distribution of caffeic acid derivatives in the Hypochaeridinae does not give a clear cut picture. The most parsimonious explanation for the observed pattern is that both caffeoyl quinic and caffeoyl tarataric were part of the secondary metabolite profile of the common ancestor of the Hypochaeridinae , and that the ability to synthesise caffeoyl tartaric acid derivatives was lost multiple times independently by some members of the subtribe. This loss is linked most probably to one or a few enzymes only. A similar mechanism was postulated by Wink (2003) to explain the distribution of particular classes of alkaloids in the Fabaceae .

Flavonoids

It is generally known that flavonoids are poor chemosystematic markers at higher taxonomic levels but excellent markers at the species level and below. Nonetheless, luteolin, the most common aglycon in the Asteraceae , seems also to be the most common aglycon in the Cichorieae tribe and the Hypochaeridinae subtribe. One aglycon of particular interest that occurs also in some members of the Hypochaeridinae is isoetin. This otherwise rare flavonoid has been found in some genera of the Cichorieae , Hieracium , and a number of genera of the Hypochaeridinae (see above).

Figures

Fig. 1 Maximum likelihood (ML) phylogram. Bootstrap support values of ML and posterior probabilities of the Bayesian Likelihood (BL) analysis are given above branches (ML/BL). H I and H II denote clades

Fig. 2 Maximum parsimony (MP) 50% majority rule consensus tree. Bootstrap support values given above branches. Clades contain species according to Fig. 1