A taxonomic study in the genus Hackelia in western North America Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/t435gg703

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  • A biosystematic study was made on the species of Hackelia of northwest America and adjacent Canada. During the course of the study 140 populations, representing all species and varieties, were transplanted to the greenhouse for study under controlled conditions. Chromosome counts were made for all 14 taxa studied, and intra- and interspecific hybridizations were attempted. For the study over 3000 specimens were borrowed from 21 herbaria in the United States and Canada. Only two chromosome levels were found: 2n=24 and 2n=48. Chromosome counts were obtained only from mitotic cell divisions, as some difficulty was encountered in making usable pollen-mother cell smears. This was especially true in the tetraploids, where normal chemical techniques for fixation of buds resulted in the chromosomes tending to stick together. Because none of the species have chromosome numbers higher than tetraploid, it was felt that polyploidy, although present, has not been a dominant evolutionary mechanism in this section of the genus. The tetraploid taxa under study probably evolved from one or two original tetraploid ancestors which underwent speciation during the Quaternary period. It was found that nutlet features were of limited value as taxonomic characters in some species of Hackelia. The nutlets of some species are highly variable with regard to surface texture, number and size of intramarginal prickles, and the length and degree of fusion of the marginal prickles, The features of the fornix of the corolla are also variable and must be used with care. The distinctness of the tetraploid taxa is maintained in part by their specific habitat requirements. They occur principally in open sites with rocky to sandy soil, where plant competition is minimal. An artificial key to the species and varieties is presented in the taxonomy section, together with complete synonymies, descriptions, lists of cited specimens, and maps of distribution. One new species is described from southeastern Oregon (Hackelia ophiobia) and one new variety from central Washington (H. hispida var. disjuncta), Hackelia diffusa (Lehm.) Johnst. is defined to include var. diffusa, var.arida (=H. arida (Piper) Johnst.) and var. cottonii (=H. cottonii (Piper) Brand).
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