141 Xiang & al. • Phylogeny of Abies TAXON 58 (1) • February 2009: 141–152 INTRODUCTION The fir genus Abies Miller consists of ca. 48 species naturally occurring in the cool temperate and boreal re- gions of the Northern Hemisphere. The genus is economi- cally important for its timber and widely cultivated as pure stands for Christmas trees in North America and Europe (Liu, 1971). It is also ecologically important for being a major component of the cold temperate forests character- izing the high altitudes and boreal regions of the Northern Hemisphere (Liu, 1971; Farjon, 1990; Farjon, 2001). As the second largest genus of Pinaceae, Abies is char- acterized by the female cones being erect on branches of the upper canopy; the seed scales and bracts falling off at cone maturity to facilitate the spreading of seeds while the cone axis remains; and lateral branchlets terminated by three hastately arranged vegetative buds from which foli- age shoots are produced (Liu, 1971; Farjon & Rushforth, 1989; Robson & al., 1993). This combination of characters is unique in Pinaceae. Cladistic analyses of Pinaceae using morphological and molecular data confirmed the mono- phyly of Abies and identified the eastern Asian genus Ketel- eeria as its closest relative (Hart, 1987; Wang & al., 2000). Keteleeria is in general very similar to Abies in morphology and anatomy (Liu, 1971), but different in a few important features. In Keteleeria, leaves are keeled on both surfaces; male cones are clustered, and seed cones are persistent on branches. Whereas in Abies, leaves are usually keeled only on the lower surface and grooved on the upper surface; male cones of Abies are solitary and mature seed cones are deciduous, with only the rachis being persistent. Although there is no disagreement regarding the monophyly of Abies, the classification within the genus has been debated among taxonomists (Engelmann, 1878; Hickel, 1906–1908; Matzenko, 1968; Liu, 1971; Farjon & Rushforth, 1989). Two different infrageneric taxonomic schemes were proposed in the most recent taxonomic re- visions of Abies (Liu, 1971; Farjon & Rushforth, 1989). Liu recognized two subgenera: Abies and Pseudotorreya. The latter includes only A. bracteata, the Santa Lucia fir, a relict species limited to the central Coast Range of California with unique morphological characters (e.g., non- resinous vegetative buds and the elongated, needle-like cusp of the seed cone bracts). The remaining species were grouped into 14 sections in subgenus Abies primarily based on morphological characters and regions of geographi- cal distribution (Table 1). Liu’s comprehensive revision of Abies was considered to represent a significant advance in understanding the systematics and classification of Abies, but was criticized for over-emphasizing the geographic distribution (Farjon & Rushforth, 1989). Farjon & Rush- forth, therefore, revised Liu’s classification and produced a subdivision scheme of the genus based on characters of female cones and vegetative structures. In contrast to Liu (1971), they did not recognize subgenera and divided the genus into 10 sections. The two schemes also differ con- siderably in their circumscriptions of sections (Table 1). For example, sect. Balsamea of Farjon & Rushforth (1989) Phylogeny of Abies (Pinaceae) inferred from nrITS sequence data Qiao-Ping Xiang 1 , (Jenny) Qiu-Yun Xiang 2 , Yan-Yan Guo 1,3 1,3 & Xian-Chun Zhang 1 * 1 1 State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, People’s Republic of China. * zhangxc@ibcas.ac.cn (author for correspondence) 2 2 Department of Plant Biology, North Carolina State University, Raleigh, North Carolina 27695-7612, U.S.A. 3 3 Graduate School of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China Abies comprises ~48 species with a disjunct distribution in the Northern Hemisphere. Despite the economic and ecological importance of the genus, phylogenetic relationships among the species remain unclear. The complete nuclear ribosomal internal transcribed spacer (ITS) region was sequenced for 31 species of Abies and its outgroup Keteleeria to reconstruct the phylogeny of the genus. The results revealed three small subrepeats with a motif (5′ -GGCCACCCTAGTC-3′ ), that is conserved across Pinaceae, and the 298 bp large subrepeats, specific to Abies occurring in all firs. Phylogenetic analysis of ITS recovered nine of the ten formerly recog- nized sections (sects. Abies, Amabilis, Balsamea, Bracteata, Grandis, Momi, Nobilis, Piceaster , Pseudopicea). The results suggest merging sect. Oiamel and Grandis. The monophyly of western North American species is suggested with robust support by ML and MP analysis. A close relationship between European and Asian species is also inferred, but with weak support. KEYWORDS: Abies, large subrepeats, nuclear ribosomal internal transcribed spacer, phylogeny, small subrepeats