Phylogenetic Relationships of Geum (Rosaceae) and Relatives Inferred from the nrITS and trnL-trnF Regions

This is a molecular phylogenetic study of the group formerly known as Dryadeae, based on DNA sequences from the internal transcribed spacers, ITS, of nuclear ribosomal DNA and the trnL intron and the trnL-trnF intergenic spacer of the chloroplast. A total of 1.9 kb, for 26 ingroup species, were analyzed using parsimony and model-based Bayesian inference. Some clades are well supported by both data sets: the ingroup, with Fallugia as the sister to the rest of the clade; Sieversia in a strict sense; a clade consisting of all the herbaceous perennials, and some clades within this last group. Other clades, within the group of herbaceous perennials, differ between the analyses. The data sets in the present study do not support any previous circumscriptions of Geum nor any of the suggested segregate genera, except for the southern hemisphere Oncostylus. Morphological characters, notably fruit characters, mapped onto the combined tree show patterns of widespread parallel evolution and reversals—or possibly the effects of reticulations. Allopolyploidy has been suggested by previous workers and there are some indications of this in our results. Geum andicola appears in different well supported groups in the two separate analyses. This may be caused by inheritance of chloroplast DNA from one parental species and homogenization of ribosomal DNA from the other. Also, the intricate fruit type present in, for example, the type species of Geum, G. urbanum, appears to have evolved twice from progenitors with plumose styles. We propose the name Colurieae for this entire clade and the name Geinae for the group of herbaceous perennials. The delimitation of Geum has varied greatly over the last century and several segregate genera have been described. Geum belongs in the Rosoideae, in the group formerly known as Dryadeae. Dryas L., however, is no longer considered to be closely related to Geum, despite similarity in fruits and embryology, but actually belongs outside the Rosoideae (Wallaart 1980; Morgan et al. 1994; Eriksson et al. 1998). The remainder of Dryadeae, about 75 species in Fallugia, Sieversia, Geum (including segregates), Coluria, Waldsteinia, and Taihangia, is the focus of this paper. This group of plants occur in temperate and Arctic regions all over the world, often at high elevations, and are most frequent in the northern hemisphere, with a few representatives occurring in South America, New Zealand, Australia, and Tasmania. Most of the species are herbaceous perennials with a rosette of imparipinnate leaves and a thick caudex, but a few species are small shrubs. The petals are yellow, white, orange, red, or purplish and the fruits are achenes. In some species the style persists on the fruit and is either hooked at the apex (Fig. 1G) or straight (Fig. 1A, D), often becoming elongate and plumose (Fig. 1A). It may also be wholly or partly deciduous (Fig. 1B, C, E, F). The length of the segment remaining on the fruit varies and it is sometimes equipped with various means of adhesion, such as bristles (Fig. 1C) or a hook at the apex. Some species (e.g., the type species of Geum, G. urbanum) have a jointed style where the terminal segment is deciduous, leaving a hooked lower segment that attaches to animals, thereby dispersing the fruit (Fig. 1E). This has been called the fish-hook fruit type (Iltis 1913). So far no morphological synapomorphies have been identified for the remainder of Dryadeae. Several species are popular garden ornamentals, such as G. coccineum Sibth. & Sm., G. triflorum Pursh, G. rhodophaeum Stoj. & Stefanov, and Waldsteinia ternata Fritsch. Some species have been used in folk medicine to treat various diseases. Pliny (77) wrote in his Natural History: ’’Geum has little roots, slender, blackish and with a pleasant smell. It not only is a cure for pains in the chest or side, but also dispels indigestion, having besides a pleasant taste’’. Recent studies have shown that the underground stems contain compounds which are effective against inflammatory diseases (Tunon et al. 1995), herpes virus infection (Kurokawa et al. 1995) and fungal diseases (McCutcheon