Thesis (M.S.)--Miami University, Dept. of Botany, 2003. / Title from first page of PDF document. Document formatted into pages; contains v, 53 p. : ill. Includes bibliographical references (p. 24-26).

This study is a taxonomic monograph of the Phacelia Crenulatae group for North America and recognizes thirty-three species and six varieties. A brief discussion of the history, general morphology, phylogeny and cytology is given. All entities are separated by a comprehensive key, followed by a list of types, synonyms, descriptions and general habitat. Distribution maps and illustrations are included. The body of this work is based on herbarium specimens and extensive field observations and collections made throughout much of western North America. These studies have resulted in the description of five new species and several nomenclatural changes.

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Tests for adaptation to three different soils inhabited by subspecific taxa within Phacelia dubia and for preadaptation to a serpentine soil were conducted to examine the plausibility of an endemic-to-endemic evolutionary pathway. Each taxon performed optimally on its home soil, demonstrating edaphic specialization. None survived on the serpentine. Hydroponic assays for tolerance to two serpentine factors, elevated magnesium: calcium and elevated nickel, were conducted on population samples and maternal half sib families. Performance was estimated by root length and rosette diameter while leaf dissection served as an indicator of developmental maturity. Both nickel and magnesium: calcium of typical serpentine inhibited all three taxa. However, the granite outcrop endemic var. georgiana tolerated higher magnesium: calcium than other taxa, its tolerance exceeded that found on its home soil, and there was developmental variation among sibships. The tolerance uncovered in the endemic var. georgiana suggests that a specialized endemic taxon may encompass variation that could lead to preadaptation to a novel habitat and therefore serve as the raw material for speciation rather than represent an evolutionary dead end.

The goal of this study was to examine the taxonomy, ecology, molecular phylogenetics and biosystematics of two apparently closely related species and to elucidate congruent patterns from these often divergent sub-disciplines of systematics. Phylogenetic analysis of DNA sequences showed that Phacelia fimbriata and Phacelia purshii are sister species that demonstrate species-specific differences in germination but little morphologic or genetic differentiation. While a geographic region of sympatry exists, elevation differences preclude co-occurrence. The widespread P. purshii supports higher levels of morphological and genetic diversity compared to the narrow endemic, P. fimbriata. Gene flow between members of this closely related species pair is blocked by hybrid inviability whose expression occurs following normal pollen tube growth and apparent fertilization. Hybrid seeds are inviable, an effect likely caused by an embryo-endosperm incompatibility that, following fertilization, permits development of maternal, but not hybrid fruit and seed tissues. This reproductive barrier adds to our knowledge of an already diverse suite of isolating mechanisms in Phacelia subgenus Cosmanthus.

Phacelia purshii, one of a few phacelias with fringed corolla lobes, has historically been described as a variety of Phacelia fimbriata or as a distinct species. The geographical range is centered on the Ohio River Valley extending north to Pennsylvania, east to the Blue Ridge, and south to Alabama. Two related species were described, Phacelia bicknellii and Phacelia boykinii, but these names were rarely used in floras or applied to herbarium specimens. A morphometric and geographic analysis of herbarium specimens showed that the description of P. bicknellii corresponds to male sterile plants and therefore does not warrant taxonomic recognition. In a sample of 280 specimens, latitudinal variation was evident in a suite of characters, some of which were associated with the historical distinction between P. purshii and P. boykinii. Two previously unrecognized diagnostic characters, pubescent ovaries and pubescent abaxial surfaces of corolla lobes, distinguished plants from the southern part of the geographic range. Both pubescence characters had a relatively abrupt transition from more or less present to absent and these corresponded to southern and northern localities, respectively. Pedicel length, the historical diagnostic character for P. boykinii, had a bimodal distribution. A discriminant function correctly assigned > 94% of specimens to northern and southern morphs when the morphs were defined by ovary pubescence. The morphological and geographical data provide for accurate diagnosis of specimens and therefore support taxonomic recognition of the southern form. That form is recognized not as a distinct species, but as a variety of P. purshii, Phacelia purshii var. boykinii.

Conservation and recovery plans for rare species require biological and ecological information to discern how they may be susceptible to human disturbances. Phacelia submutica is a threatened annual species in western Colorado. Human activities including energy development, recreation, and livestock grazing are occurring within the species’ range. To provide conservation practitioners with a scientific basis for management, this research aimed to elucidate elements of the species’ ecology. Chapter 2 describes the reproductive biology of P. submutica. Potential insect pollinators were not observed during two years of observations. Floral traits and development ensure self-pollination and reduce the likelihood that insects would be effective pollinators. Hand pollination experiments using varying pollen sources did not result in significant differences in seed number and mean mature seed weight per fruit, two metrics of reproductive success. These results indicate that the species is habitually autogamous. Conservation of this species will not require the protection of pollinators and their habitat, but should consider the potential impacts of autogamy on the species’ genetic diversity. Chapter 3 examines aspects of P. submutica’s seed ecology as they relate to the development and maintenance of the seed bank. Observations suggest seeds are limited in their long-range dispersal capacity. Average seed bank density was low (74 seeds per m2) and seeds were highly aggregated within sites. Based on three years of seed burial data, the species forms a long-term persistent seed bank that maintains high proportions of viability in drought years, but germinates prolifically in favorable years. Projections of seed depletion rates from this dataset predicted longevity to be between four and six years. Finally, seeds were generally unresponsive to germination trials involving varying degrees of cold-moist stratification, incubation temperatures, and scarification. P. submutica shows adaptations that promote its persistence in an arid environment characterized by climatic variability. Appropriate management of this species will require protection of the seed bank and the dynamics involved in its replenishment and maintenance. Chapter 4 presents implications of the two major studies and provides conservation practitioners with an integrated assessment of the results and how they relate to management.

For neutral genes, uniparental inheritance is expected to reduce effective population size relative to biparentally inherited genes. In finite populations, the ensuing genetic drift can cause stronger spatial and temporal differentiation. An intrapopulation polymorphism in chloroplast DNA was used to examine relative spatial and temporal population structure of chloroplast and allozyme markers in the annual plant Phacelia dubia. There was significant differentiation among populations at chloroplast markers but not for allozyme loci. A fine-scale analysis showed significant structure among sites within populations for chloroplast markers and local heterozygote deficiencies at allozyme loci. These spatial analyses suggest that gene flow via pollen exceeds that via seed. Temporal variation in chloroplast markers, assessed over a 10-year period, was evident in two of four populations, and allozyme loci were characterized by temporal variation in rare-allele frequencies. Population structure appeared to be related to the intensity and type of human disturbance influencing each population. Habitat destruction promoted isolation and enhanced differentiation, whereas mowing increased seed dispersal and reduced differentiation for chloroplast markers. At this time, genetic drift appears to be the primary force shaping chloroplast gene frequencies.

Occurrences of Phacelia dubia in the Piedmont of South Carolina have been taxonomically enigmatic. Prior work had shown that there was partial reproductive isolation when plants from South Carolina were hybridized with any of the other varieties but evidence of morphological differentiation was lacking. In this study, a new morphological analysis showed South Carolina plants differed significantly in corolla lobe size, sepal size, and leaf dissection in comparisons with neighboring varieties, P. dubia var. dubia and P. dubia var. georgiana. A preponderance of evidence showing differentiation from all other varieties supports recognition of a new variety, P. dubia var. rionensis. Field work and an updated analysis of herbarium records showed the new variety is found in nine contiguous counties in the central and northern Piedmont of South Carolina and two counties in the inner Coastal Plain. We posit a hypothesized biogeographic pathway based on migration of a P. dubia ancestor from the Great Plains or Mexico to the Nashville Basin cedar glades, then to South Carolina piedmont granite outcrops, followed by a migration south to Georgia and Alabama piedmont granite outcrops and a separate migration north to rocky woodlands in North Carolina.

Phacelia purshii Buckley and P. fimbriata Micheaux are two species that are nearly morphologically indistinguishable. Seed germination experiments showed that the high elevation endemic, P. fimbriata requires lower temperatures to trigger germination. Following interspecific crosses, pollen tubes enter ovules and maternal tissue of the gynoecium matures but hybrid diploid and triploid organs fail to develop. DNA sequences from the ribosomal DNA internal transcribed region showed that P. fimbriata and P. purshii comprise a monophyletic clade but that P. fimbriata is more differentiated from related species. In contrast, P. purshii supported significantly higher levels of intraspecific polymorphism. Phacelia fimbriata and P. purshii are sister species with similar morphology but they are unable to hybridize, they are differentiated in physiological characteristics related to environment, and they inhabit different elevations. This pattern of relationship and differentiation suggests P. fimbriata may be the product of ecological speciation.