A fossil-calibrated phylogenetic framework based on exemplars from each of the four taxonomic sections within Pinus was created using multiple nuclear and chloroplast loci. Calibration at the well-defined subgeneric split within Pinus with either fossil leaves and cones (ca. 45 million years ago) or fossil wood (ca. 85 million years...
In addition to its longstanding recognition as an influential evolutionary process, interspecific hybridization is increasingly regarded as a potential threat to the genetic integrity and survival of rare plant species, manifested through gamete wasting, increased pest and disease pressures, outbreeding depression, competitive exclusion, and genetic assimilation. Alternatively, hybridization has also...
The thesis begins with an introduction to signal transduction
and an analysis of current understanding of plant signal
transduction. There are similarities between plants and animals,
but also key differences, including lack of protein kinase C and of a
cAMP signaling pathway in plants, and presence in plants of
calcium...
Eight species of Lathvrus (Fabaceae, Faboideae) endemic to the
Pacific Coast of North America were the subject of a systematic
investigation. Taxa studied included Lathvrus vestitus, Nutt. ex T.
& G., L. laetif lorus Greene, L.. iepsonii Greene, £,. splendens
Kellogg, L. polvphvllus, Nutt. ex T. & G., L. holochlorus...
The study of the infra-specific ranks (i.e., subspecies and variety) can be considered
the study of the process of speciation. Astragalus lentiginosus Douglas ex Hooker
(Fabaceae) is the most taxon rich species in the U.S. flora currently including 40
taxonomic varieties. These varieties were described using traditional taxonomic
methods primarily...
The relative role of cospeciation and host switching in the phylogenetic history of
ascomycete foliar symbionts is addressed in the orders Leotiales and Rhytismatales, fungi
associated predominantly with Pinaceae (Coniferales). Emphasis is placed on comparing
the evolution of the sister genera Pseudotsuga and Larix (Pinaceae) with that of the
pathogenic...
Managers of forest and plantation ecosystems are encountering growing problems involving plant pathogens and the expanding geographic ranges of these pathogens. Historically unexposed stands are exceptionally vulnerable when a non-native pathogen is introduced because these pathogens can cause devastating disease in a host population that lacks co-evolved resistance mechanisms. One...
Plant sexual reproduction requires a broad array of molecular mechanisms to proceed successfully. Some of these mechanisms are well-studied, but our knowledge of them as a whole is fundamentally incomplete. Pollen tube growth is a key part of this process, facilitating the delivery of the sperm cells to the female...