Island systems are generally more sensitive to the introduction of non-native species than comparable mainland systems and are particularly vulnerable to disturbances that create opportunities for invasion. We examined the impact of browsing by introduced deer on seedling establishment and physiology in three obligate seeding (i.e., non-resprouting) species on Santa Catalina Island for two years following a large fire in 2007: Arctostaphylos catalinae P. Wells (Ericaceae), Ceanothus arboreus E. Greene (Rhamnaceae), and Ceanothus megacarpus Nutt. var. megacarpus (Rhamnaceae). Four post-fire sites were established, with each site containing 12-20 plots exposed to browsing and 12-20 control plots protected from deer browsing. Browsing did not significantly affect seedling survival or physiology in C. arboreus, the only species to experience significant browsing; browsing did, however, significantly reduce seedling height. Predawn and midday water potentials, stomatal conductance, and growth differed among species during their first post-fire dry season. Arctostaphylos catalinae experienced the lowest dry season predawn water potentials (-3.3 MPa compared to -1.7 MPa for C. arboreus and -2.2 MPa for C. megacarpus). Ceanothus arboreus and C. megacarpus exhibited relatively high seedling survival (56% and 69%, respectively) and high resistance to xylem cavitation of stems (P₅₀ = -6.0 and -6.7 MPa, respectively), compared to A. catalinae which had lower seedling survival (30%) and was less resistant to cavitation (P₅₀ = -4.2 MPa). Browsing significantly impacted seedling height, which could impact stand structure. Differential browsing pressure and seedling resistance to water limitation may have important consequences for long-term distribution and abundance of these island endemics on Santa Catalina Island.

Del Mar manzanita (Arctostaphylos glandulosa Eastw. subsp. crassifolia (Jeps.) P.V. Wells) is a federally listed endangered shrub found in San Diego County, California and Baja California, Mexico. This manzanita forms part of the imperiled southern maritime chaparral of southwestern California and adjacent Baja California, Mexico. Del Mar manzanita is problematic to identify because of morphological intergradation with other subspecies of A. glandulosa. Such intergradation could result from biological phenomena, such as gene flow among subspecies. Alternatively, it could be that the current circumscription of the Del Mar manzanita is not correct, and that the morphological characters used to diagnose this subspecies are inaccurate indicators of underlying genetics. This situation leads to problems for conservation planning, where accurate identification of individual plants is essential. Here, we used high-throughput sequencing of restriction-site associated DNA markers (RADseq) to develop single nucleotide polymorphism (SNP) data for a large sample of putative Del Mar manzanita, and a small sample of closely related subspecies of A. glandulosa. We analyzed genetic relationships using a total of 65,964 SNPs, with the aim of testing whether morphological traits used to identify Del Mar manzanita are an accurate reflection of underlying genetic patterns. We conclude that vegetative morphology is a poor predictor of genetic patterns, and that the current morphology-based circumscription of Del Mar manzanita is probably in need of some change. However, due to the limited sampling of A. glandulosa subspecies in this study, it is not possible to determine the taxonomic limits of Del Mar manzanita using our SNP data.

The conservation status of the northern California black walnut (Juglans hindsii (Jeps.) Jeps. ex R. E. Sm.) has been a source of considerable confusion and controversy. Although not currently legally protected by either Federal or State Endangered Species Acts, this species is given conservation status by the California Native Plant Society and the California Department of Fish and Wildlife, and some California counties require mitigation for removal of individuals of this species, especially older trees. Despite the current widespread distribution in northern California and southern Oregon of trees that match J. hindsii morphologically, there are only three or four sites where the species is known to have occurred prior to extensive settlement of California by Europeans in the mid-19^th century. This has led to the suspicion that trees found in other places may not be genetically pure J. hindsii but may instead be descendants of lineages that experienced past gene flow from one or more other species. In addition, despite its more distant relationship, the cultivated walnut (J. regia L.) readily hybridizes (as the male parent) with J. hindsii, producing morphologically identifiable ‘Paradox' hybrids, which occur spontaneously and are widely planted as rootstocks and street trees. Finally, recent collections of J. hindsii from southern California have raised questions about the respective geographic distributions of J. hindsii and southern California black walnut (J. californica S. Watson). We analyzed genotypes at 10 microsatellite loci for 158 mostly wild J. hindsii trees, as well as some orchard waifs, from 10 counties in northern and southern California and one county in southern Oregon, including representatives of putative original native populations. We also sampled several Paradox hybrids, 10-20 standards for each of the five North American black walnut species, and six standards for J. regia. Bayesian cluster analyses with the program STRUCTURE revealed that at least 71.5% of the putatively wild J. hindsii represent genetically pure members of that species, while the remaining trees show evidence of past hybridizations with one or more of the other North American black walnut species. We found no evidence of introgression of J. regia into J. hindsii. The results suggest that individual J. hindsii trees should not have conservation status.

Two related species of Trifolium L. endemic to western North America, T. variegatum Nutt. s. l. and T. polyodon Greene, are studied. Multivariate analyses and morphological differences suggest that three species should be recognized instead of two. Trifolium variegatum is divided into two species: T. appendiculatum Lojac. and T. variegatum. Trifolium appendiculatum (including T. rostratum Greene) is a large-flowered species endemic to California and southern Oregon. Trifolium variegatum is found throughout western North America and remains the most diverse, but is now circumscribed by a consistent floral morphology. Trifolium polyodon is restricted to the Monterey peninsula and has distinctive calyx lobe teeth; its circumscription remains unchanged.