Wyethia

Abstract: Genetic structure arises when limited gene flow between populations favours the development of distinct arrays of genetic characters within each population. Determining the spatial scale at which this differentiation occurs is critical to our understanding of population biology and microevolution of species. The genetic structure and spatial pattern of genetic variation in an endemic, clonal perennial, Wyethia reticulata E. Greene, was investigated using random amplified polymorphic DNA (RAPD) markers and allozyme alleles. Large stands (250–360 m2) were found to contain few genetic individuals. Despite the small population sizes and endemism of the species, W. reticulata was highly diverse genetically, with most of the variation (75–81%) distributed within populations. A population structure in full agreement with spatially defined populations was achieved only by combining RAPD and allozyme markers. Analysis using both types of markers appeared to provide estimates of genetic similarity between individuals that were most consistent with empirical data on plant distributions. We postulated that large, long-lived clones dominated genetic relationships within populations but also provided opportunities for gene flow between populations on a longer time scale. The two marker types yielded different estimates of between-individual similarity and revealed disparate patterns of population structure. This result will arise because allozymes and random DNA segments have dissimilar evolutionary dynamics with respect to mutation and selection.

Abstract: Phylogenetic analysis of chloroplast DNA restriction site data for 76 of the 302 genera of Heliantheae sensu lato using 16 restriction endonucleases reveals that subtribe Ecliptinae is polyphyletic and that its genera are distributed in four different lineages. The ecliptinous genera Squamopappus, Podachaenium, Verbesina , and Tetrachyron (of the Neurolaeninae), along with other members of subtribe Neurolaeninae are the basalmost clades of the paleaceous Heliantheae. The mostly temperate species of subtribe Ecliptinae (exemplified by Balsamorhiza, Borrichia, Chrysogonum, Engelmannia, Silphium, Vigethia, and Wyethia) are strongly nested in a clade with the Mesoamerican monotypic genus Rojasianthe as basal. The genera characterized by marcescent ray corollas traditionally classified in subtribe Zinniinae constitute a strongly supported group sister to Acmella, Spilanthes, and Salmea. The largest clade of ecliptinous genera is the most recently derived group within Heliantheae sampled. This large group of mostly Neotropical lowland genera (variously characterized by their winged cypselae, foliaceous phyllaries, and opposite phyllotaxy and exemplified by Perymenium, Wedelia,and Zexmenia) has been and continues to be the most challenging group from a taxonomic standpoint. The study provides new insights as to their relationships that will have a positive impact in future monographic studies of the group. The genera of the Espeletiinae form a monophyletic clade and are sister to members of the Milleriinae and Melampodiinae. This result is consistent with their traditional taxonomic placement with genera such as Smallanthus with which they share a tendency for functionally staminate disc flowers. The phylogenetically enigmatic genus Montanoa is sister to Melampodium. Members of subtribe Galinsoginae are clustered in two main lineages that correspond to the traditional division of the subtribe based on pappus characteristics. There is no support for the monophyly of subtribe Galinsoginae, and the same results indicate some of its genera are paraphyletic. Tribe Heliantheae sensu lato includes ;3500 species classified in 302 genera (Robinson, 1981; Karis, 1993; Karis and Ryding, 1994). The tribe includes many wellknown plants such as the commercial sunflower cultivars of several Helianthus species, and many ornamentals including members of Cosmos, Coreopsis, Dahlia, and Tagetes. Its distribution is essentially New World with a few genera extending into the Old World tropical and subtropical regions. The tribe is predominantly North American with a high number of species concentrated in the highlands of Mexico and the southwestern United States, and comparatively smaller numbers in the Andes and southwestern Brazil. The highest generic diversity is in Mexico. The taxonomic circumscription of the Heliantheae has been modified through time to include all genera with mostly trinerved leaves, yellow corollas, and radially or laterally flattened cypselae. This general taxonomic con1

Abstract: Reference is made with increasing frequency in plant taxonomic literature to the occurrence in nature of interspecific hybrids: Ceanothus (McMinn, 1942), Sctlvza (Epling, 1942), Balsamorhiza (Ownbey and Weber, 1943), Clematis (Erickson, 1945), Wyethia (Weber, 1946), and Aquilegia (Munz, 1946), to cite some of the more recent. In these examples, so far as the reader is able to judge, F1 hybrids, backcrosses and even hybrid swarms may occur. Because of the weak intrinsic barriers between species. which characterize these and many other plant groups, the assumption might logically be made that gene flow between the species concerned would obliterate or blur the specific morphological differences if long continued. Yet the taxonomic treatment in such papers suggests that the constancy of the species concerned has not been materially affected. The observations which follow seem to confirm this latter view and to indicate that gene flow from species to species does not ordinarily occur, or if so, at a level difficult to distinguish from expected intraspecific variation, even though continued hybridization may seemingly provide a channel.