American Journal of Botany 96(10): 1907–1921. 2009. T HE EVOLUTIONARY ORIGIN OF A SECOND RADIATION OF ANNUAL C ASTILLEJA (OROBANCHACEAE) SPECIES IN SOUTH AMERICA: THE ROLE OF LONG DISTANCE DISPERSAL AND ALLOPOLYPLOIDY 1 David C. Tank 2,3,4 and Richard G. Olmstead 3 2 Department of Forest Resources & Stillinger Herbarium, College of Natural Resources, University of Idaho, P.O. Box 441133, Moscow, Idaho 83844-1133 USA; and 3 Department of Biology & Burke Museum of Natural History, University of Washington, Box 355325, Seattle, Washington 98195-5325 USA Considerable attention has been directed toward understanding the wide gaps in range that are common among many groups of closely related organisms. By placing their biology and geography in a phylogenetic context, we may gain a broader knowledge of the series of historical events that have led to present species distributions. In addition to the North American annuals, a second radiation of annual Castilleja species is in Andean Peru and central Chile. Phylogenetic analyses of chloroplast and nuclear DNA regions revealed a complex history for the origin and diversifi cation of annual Castilleja species in South America. In addition to at least three independent long-distance dispersal events from North America, allopolyploidy has played a signifi cant role in this disjunct radiation. Only C. attenuata occurs in both California and South America, and these results support its recent arrival to central Chile. Two Peruvian species are inferred to be allopolyploids; hybridization between annual lineages derived from inde- pendent long-distance dispersal events from North America gave rise to C. profunda , and hybridization between South American annual and perennial species gave rise to C. cerroana . The relative importance these events are discussed with reference to the observed morphological, ecological, and distributional patterns. Key words: amphitropical disjuncts; biogeography; Castilleja ; GBSSI; granule-bound starch synthase/invertase; Indian paintbrush; Orobanchaceae; Peru; waxy . Geographic disjunctions have intrigued biogeographers and disjunctions: “ The new data have, moreover, served to broaden evolutionary biologists and have often been the source of imag- the parameters of taxonomy, at the same time strengthening its inative explanations for the wide gaps in range that are common framework and providing new clues that help to untangle knotty among many groups of closely related organisms. Early work- evolutionary problems. ” ers in plant biogeography (e.g., Axelrod, 1958 ; Florin, 1963 ; Temperate plant groups that are distributed primarily in Raven, 1963 ; Good, 1964 ; Cruden, 1966 ; Thorne, 1972 ) recog- western North America, but are also represented in part in the nized the role that present distributional patterns play in our South American fl ora, are likely to be the result of two basic interpretations of the past history of organisms and the regions distributional pathways. First, there are those montane groups that they occupied. However, to correctly interpret the series of that are more or less continuously distributed at high elevation events that have led to present species distributions, we must across the American tropics and found in Andean South Amer- place the biology and geography of the group of interest in a ica, e.g., Lupinus ( Hughes and Eastwood, 2006 ), Viburnum phylogenetic context. Although he did not use the term phylo- ( Winkworth and Donoghue, 2005 ), Valerianaceae ( Bell and genetic, Wood (1972, pp. 107 – 108 ) recognized that new sources Donoghue, 2005 ), to name a few. This type of distribution is of data brought to plant taxonomy by the then emerging fi eld of likely the result of the continuous or “ stepping stone ” migration biosystematics would be essential to understanding biological and diversifi cation of these taxa through the western mountain systems that connect the two continents ( Thorne, 1972 ). In ad- dition, there are other groups that are disjunctly distributed in 1 Manuscript received 9 December 2008; revision accepted 27 May 2009. the temperate regions of both continents. Amphitropical tem- The authors thank J. Ammirati, T. Bradshaw, J. M. Egger, B. Moore, and two anonymous reviewers for critical comments on the manuscript, and J. perate disjunctions are well known between North and South M. Egger, M. Zapata, S. Leiva, A. Sagastegui, and M. Dillon for assistance America, and there are at least 65 genera representing ~130 facilitating fi eldwork in Peru. This research was supported by a Graduate species, species pairs, or species complexes in the Americas Fellowship in Molecular Systematics from the University of Washington that correspond to this distribution ( Raven, 1963 , 1972 ; Thorne, Department of Botany, the Research Award for Graduate Students from the 1972 ). Most species with this type of distribution are restricted American Society of Plant Taxonomists, the Karling Graduate Student to the mediterranean climates of the Pacifi c coast and are most Research Award from the Botanical Society of America, the Award for frequent between California and Chile ( Raven, 1963 ). Because Graduate Student Research from the Society of Systematic Biologists, the these temperate amphitropical disjuncts are mostly not montane Sigma Xi Grants in Aid of Research from the University of Washington in their distributions, migration via long-distance dispersal has Chapter, and the Giles Award for Graduate Student Field Research from been the preferred hypothesis to explain their disjunct distribu- the University of Washington Department of Botany to D.C.T., the NSF Doctoral Dissertation Improvement Grant DEB-0412653 to R.G.O. for tions (e.g., Raven, 1963 , 1972 ; Thorne, 1972 ). Furthermore, D.C.T., and the NSF grant DEB-0090313 to R.G.O. Raven (1963) concluded that the recurrent pattern of closely 4 Author for correspondence (e-mail: [email protected]) related disjunct species in western North and South America was the result of long-distance dispersal of seeds via migratory doi:10.3732/ajb.0800416 birds. However, disjunct distributions between the hemispheres 1907 1908 American Journal of Botany [Vol. 96 could also arise through a series of short dispersals over time history of this species is poorly understood. Our own observa- following the mostly continuous western American mountains tions suggest that this species may in fact be annual, but may be through the tropics, accompanied by extinction in the tropics able to persist given the right environmental conditions. Al- and diversifi cation in the temperate regions ( Cruden, 1966 ; though the root of this species is robust in some individuals, Thorne, 1972 ). In this paper, we examine a complex distribu- observation of plants in the fi eld, as well as numerous herbar- tional pattern among annual and perennial Castilleja species ium specimens, has revealed no conclusive evidence of peren- (the paintbrushes) in North and South America that includes niality (i.e., ± woody caudex or old stems from previous years). both widely disjunct annuals and continuously distributed mon- The corolla morphology of C. cerroana is very similar to the tane perennials, and we provide a framework for the origin of annual Castilleja species (i.e., well-developed lower corolla lip the present distributional patterns in the context of a robust phy- with a more or less infl ated pouch that is evidently toothed); logenetic hypothesis. however, the calyx of C. cerroana is more similar to many pe- rennial Castilleja species ( Fig. 1C ). Members of the Onco- Biology and distribution of South American Castilleja— Cas- rhynchus grade have a calyx that is cleft more or less equally on tilleja comprises approximately 180 mostly perennial species all sides (i.e., subequally cleft; Fig. 1A and 1B ), while the ma- found primarily in western North America and Mexico, but with jority of perennial Castilleja species have an unequally cleft about 20 species distributed in Central and South America, in- calyx (i.e., cleft deeper in the front and back than on the sides; cluding a small group of annual species distributed primarily in Fig. 1D ). The unequally cleft calyx of C. cerroana is unique Andean Peru. This large and taxonomically complex genus rep- among the group of closely related species in northern Peru; resents the majority of the hemiparasitic subtribe Castillejinae G. however, this feature is also seen in C. laciniata , one of two Don (tribe Pedicularideae Duby, Orobanchaceae Vent.). Within more southerly distributed South American annual species. Castillejinae, perenniality is restricted to Castilleja , where the The remaining South American species assigned to sect. On- large majority of species (~160 spp.) are perennial herbs. Con- corhynchus were all newly described by Chuang and Heckard trary to the commonly held view that annuals are derived from (1992) . These four species, C. alpicola , C. peruviana , C. pro- perennials (e.g., Stebbins, 1957 ), phylogenetic relationships in- funda , and C. vadosa , are primarily restricted to the open, high ferred from separate and combined analyses of chloroplast (cp) elevation Jalca habitat (i.e., semiarid Andean grasslands) that and nuclear ribosomal (nr) DNA regions have revealed that the dominates the Peruvian highlands ( Fig. 1 ). Of these species, C. perennial Castilleja species evolved from a grade of annual lin- alpicola is the most restricted in its range and is only known eages in Castillejinae, including the majority of the annual Cas- from the type locality