Edaphic-endemic plant taxa are often interpreted as recently derived entities that evolved in situ, with genetic divergence driven by substrate specialization. However, little is known about the evolution of specific edaphic-endemic taxa, particularly the role that soil conditions may play in their initial divergence and continued persistence. Our study focuses on Ceanothus roderickii, a strict specialist on soils derived from a single outcrop of the geological material gabbro located in south-western El Dorado County, California. In order to elucidate the evolutionary history of C. roderickii we sequenced the third intron of the low-copy nuclear gene nitrate reductase (NIA) for individuals representing four populations of C. roderickii and a wide taxonomic and geographic sampling of closely related plants, including 37 populations of Ceanothus cuneatus and a single representative from 16 other taxa. Analysis of NIA shows that C. roderickii is closely related to C. cuneatus var. cuneatus, a widely distributed taxon found on a diversity of soils. Ceanothus cuneatus var. cuneatus is paraphyletic and comprises two major geographic groups, one coastal and one interior, the latter containing C. roderickii. Thirteen soil chemistry variables were assayed in 42 populations of C. cuneatus representing the wide geographic range of this species, and in 10 populations of C. roderickii. Analysis of these data indicates that evolution of C. roderickii was associated with specialization to nutrient-deficient forms of gabbro-derived soil. Soil chemistry associations of C. cuneatus var. cuneatus and C. roderickii are most divergent where the species come into close contact on gabbro, with C. cuneatus var. cuneatus occupying comparatively nutrient-rich forms of gabbro-derived soils, a result that is consistent with reinforcement.

The pollination ecology of Darlingtonia californica Torr., including especially the identity of its pollinators, has remained enigmatic for more than a century. The flowers of this well-known charismatic species are unusual in form and color, and have been the subject of much speculation. Accordingly, in this study we sought to identify D. californica's floral visitors and determine their potential effectiveness as pollinators, in the context of D. californica's unusual floral morphology. We also used hand-pollinations and emasculations to determine whether plants were pollen-limited at five study sites in northwest California, and to evaluate the potential for self-pollination in natural populations of D. californica. A generalist solitary bee, Andrena nigrihirta, visited and pollinated D. californica flowers at five sites in northern CA. Despite very low visitation rates, individual flowers at all study sites were predicted to receive at least one visit by A. nigrihirta. Other regular floral visitors included thrips and several species of spiders. Plants at all five study populations were found to be pollen-limited with respect to the number of seeds produced per capsule. Fruit and seed production by emasculated flowers indicated a large degree of cross-pollination. However, emasculated flowers did not produce as many fruits and seeds as unmanipulated flowers, suggesting that self-pollination contributes to D. californica reproductive success as well. Observations of A. nigrihirta on flowers revealed that the shape and orientation of D. californica's ovary and petals promote stigma contact both when pollinators enter and exit a flower, contrary to previous thought. Our findings provide evidence that D. californica is melittophilous, and suggest a resolution of the long-standing mystery surrounding the pollination of this rare species.

The aim of this study was to clarify the relationships between Elymus alaskanus and E. violaceus in northwest North America. We performed a morphological and biogeographic analyses of ca. 300 widely distributed herbarium specimens. Following a univariate analysis of morphological characters used in contemporary treatments, we found no clear character, or combination of characters, that differentiates unambiguously among the taxa at the specific level. However, glume and lemma trichome length reliably separated E. alaskanus subsp. hyperarcticus from other taxa. Specimens could not be differentiated at the specific level by habitat preferences or geographic distribution as described in the most current treatments. Further, principal components analysis and cluster analysis were unable to reliably segregate specimens into groups. Discriminant analysis reliably grouped E. violaceus and E. alaskanus subsp. hyperarcticus, but not E. alaskanus specimens. In the development of a relevant treatment for E. alaskanus and E. violaceus, we recommend that (i) E. violaceus be treated as a subspecies of E. alaskanus and called E. alaskanus subsp. latiglumis, and (ii) E. alaskanus subsp. alaskanus and E. alaskanus subsp. hyperarcticus continue to be recognized at the subspecific level.

The species Mentzelia thompsonii Glad was published in 1976 based solely on herbarium material, and it is the only species in Mentzelia section Trachyphytum that has not been examined cytogenetically. Here we report that M. thompsonii is diploid (2n  =  18), making it the easternmost diploid species in section Trachyphytum and the only one that does not occur in California. The diploid status and edaphic specialization of M. thompsonii suggest that it is a paleoendemic isolated from other diploids in Trachyphytum by specialization during Pleistocene climate change. Our investigations have also uncovered confusion in the literature and herbaria regarding the taxonomy of M. thompsonii and its overall place within Mentzelia. Mentzelia thompsonii has been synonymized with Mentzelia humilis (Urb. & Gilg) J. Darl. (a member of section Bartonia) in several prominent databases and herbaria. To the contrary, our studies reveal that M. thompsonii is distinct from M. humilis; furthermore, as a unique component of Colorado Plateau diversity, it is critical for inferences of biogeographic evolution in section Trachyphytum.

A new species Mentzelia monoensis Brokaw and Hufford, endemic to Mono County, California, is described. Mentzelia monoensis, a hexaploid, is most similar to two widespread species, M. montana (Davidson) Davidson (tetraploid) and M. albicaulis (Douglas ex Hook.) Douglas ex Torr. & A. Gray (octoploid). The three species can be distinguished based on differences in floral bracts, fruits, and seeds. Mentzelia monoensis is commonly found in volcanic soils derived from the eruptions of Mono Craters and may exhibit edaphic specializations that limit its distribution.