An ITS-Based Phylogenetic Analysis of the Perennial, Endemic Apiaceae Subfamily Apioideae of Western North America

Phylogenetic analyses of 159 DNA sequences from the nuclear rDNA internal transcribed spacer regionwere conducted to evaluate the monophyly of the herbaceous, perennial genera of Apiaceae subfamily Apioideae endemic to North America (north of Mexico) and to determine the relationships of those elements that currently comprise Cymopterus within the group. The results of a previous phylogenetic study were equivocal in suggestingmonophyly for these perennial, endemic taxa and revealed Cymopterus to be polyphyletic, with its species closely linked with those of Aletes, Lomatium, Musineon, Oreoxis, Orogenia, Podistera, Pseudocymopterus, Pteryxia, and Tauschia. Herein, we expand sampling to include comprehensive representation of Aletes, Cymopterus, Musineon, Oreoxis, Orogenia, Podistera, Pseudocymopterus, and Pteryxia, and greater representation of Lomatium and Tauschia. We also include all members of two genera not examined previously,Glehnia and Oreonana, as well as additional outgroup genera from the Angelica clade of the apioid superclade. Our results indicate that the perennial, endemic apioid umbellifers of North America constitute a (weakly supported) monophyletic group, with Angelica and the meso-American Arracacia clade comprising two of several possible sister groups. The two subspecies of Glehnia littoralis ally with Angelica and Peucedanum japonicum; Oreonana shows afŽnity with several species of Cymopterus and Lomatium. The lack of resolution in the ITS trees precludes unambiguous hypotheses of relationship among these perennial, endemic umbellifers but does show that many of these genera, where resolved, are not monophyletic. Indeed, Cymopterus and Lomatium are highly polyphyletic and permeate all major clades resolved in the molecule-derived trees. Evidence from branch lengths and low sequence divergence suggests that this group of North American umbellifers underwent rapid radiation, likely during the geoclimatic events of the Late Tertiary and Quaternary. Cymopterus Raf. (Apiaceae subfamily Apioideae), the spring-parsleys, comprises some 35 species (Kartesz 1994) of herbaceous perennials distributed largely throughout western North America (NA). Approximately two-thirds of these species are restricted to the Great Basin region, roughly bounded by the SnakeRiver of Idaho, Sierra Nevada of California, Colorado River of Arizona, and the Rocky Mountains of Colorado (Mathias 1965). Many species are xerophytic or semixerophytic, being conŽned to dry, sandy, or alkaline habitats. They are low in stature, possess thickened, deep taproots, and have ternately cleft, compound or dissected leaves. The inorescence is an open compound umbel, and the owers are mostly yellow or white, opening from very early in the spring to throughout the summer. Most distinctive, however, is their fruit, for the two marginal (lateral), and usually one or more of the three dorsal ribs, are conspicuously winged. These wings may be membranous to spongycorky, and variously plane to wavy or corrugated. Indeed, the generic name is derived from the Greek kyma, a wave, and pteron, a wing, referring to the often undulate wings of the fruit. Much confusion exists with regard to the proper delimitation of Cymopterus and its relationship to the other indigenous umbellifers of western NA (whose ranges extend from southern Canada to northern Mexico). These genera include Aletes J.M. Coult. & Rose, Glehnia F. Schmidt ex Miq., Harbouria J.M. Coult. & Rose, Lomatium Raf.,Musineon Raf., NeoparryaMathias, Oreonana Jeps., Oreoxis Raf., Orogenia S. Watson, Podistera S. Watson, Pseudocymopterus J.M. Coult. & Rose, Pteryxia (Nutt. ex Torr. & A. Gray) J.M. Coult. & Rose, and Shoshonea Evert & Constance (Mathias 1930; Evert and Constance 1982; Downie et al. 2002). All are perennial taprooted herbs and many are similar to Cymopterus in their primarily low-growing and acaulescent or subcaulescent habit. Lomatium is the largest genus, with 78 species; Glehnia, Harbouria, Neoparrya, and Shoshonea are monospeciŽc, and the remainder comprise some 2–6 species each (Kartesz 1994).Considered collectively, these plants present such a confusing intergradation of similar characteristics that generic delimitation is made exceedingly difŽcult, and in the absence of mature fruits, many species are essentially indistinguishable (Jones 1908; Mathias 1930; Theobald et al. 1963; Weber 1984; Cronquist 1997; Downie et al. 2002). Cronquist (1997) included Oreoxis, Pseudocymopterus, and Pteryxiawithin a broadly circumscribed Cymopterus (Hitchcock and Cronquist 1961; Cronquist 1997). Cronquist (1997) also stated that the distinction between Cymopterus and Lomatium, i.e., the conspicuously winged dorsal fruit ribs of the former, ‘‘is subject to failure.’’ Phylogenetic studies of these endemic and largely cordilleran genera are few and have focused almost exclusively upon Lomatium (Schlessman 1984; Simmons 1985; Gilmartin and Simmons 1987; Soltis et al. 1995; Soltis and Novak 1997; Hardig and Soltis