Scientist:
Dr. Fred Hrusa

Rhododendron occidentale is restricted to the west coast of North America from southern Oregon south through the California North Coast Ranges and Sierra Nevada, reaching the Peninsular Ranges of San Diego County. It is a long-lived shrub restricted to mesic habitats. Variation patterns among 36 populations were analyzed via principal components and clustering procedures using morphological characters and isozyme alleles separately and in combination. Four datasets were examined; 1) intra-population frequencies of 42 isozyme alleles at seven loci from four enzyme systems; 2) allele presence/absence; 3) 38 morphological characters; and 4) combined allele-frequency / morphology. Results show three allopatric groups representing respectively the Klamath Ranges, the California central coast from Humboldt County to Monterey, and the Sierra Nevada/Peninsular Ranges. Based on a diagnostic morphological character subset, discriminant functions were calculated capable of separating the populations into these three groups. 602 herbarium, personal, and previously synonymized specific and intraspecific nomenclatural type specimens were then classified. Results indicate the Azalea occidentalis T. & G. lectotype represents the California central coast form; the Rhododendron occidentale var. paludosum Jeps. holotype is a Klamath Range form, and the Azalea california T. & G. lectotype (ined.) is a Sierra Nevada/Peninsular Range form. These types are recognized here as varietas' within a broadly defined Rhododendron occidentale. Rhododendron sonomense Greene is a minor variant referable to var. occidentale, and thus remains in synonymy. Environmental, phenological, and population genetic parameters were examined for correlations among these taxa. Rhododendron occidentale varietas' occidentale and paludosum are confined to equable climates, regions of low evapo-transpiration and low and high precipitation respectively. Varietas occidentale has low heterozygosity and low allelic variation; var. paludosum has low heterozygosity and moderate allelic variation. Varietas californicum occurs in low equability high evapo-transpiration climates; it has high heterozygosity and high allelic variation. The putative history of Rhododendron occidentale and its variation sources are discussed. Morphologically and allelicaly variable populations in exposed, low-elevation serpentine habitats of the inner North Coast Range, originated as hybrids between vars. californicum and paludosum; they are currently isolated phenologically. Hybridization and its possible adaptive advantages in this habitat are discussed.

Scientist:
Dr. Dean Kelch

Scientist:
Dr. Dean Kelch

Scientist:
Dr. Fred Hrusa

Since its introduction to North America in the mid 19th century, the invasive weed Salsola tragus sensu auct. (russianthistle), has become a widespread and troublesome plant pest. Early biocontrol attempts had achieved only partial success. Efforts to improve chances for success in renewed biocontrol research efforts revealed that there are actually two distinct, often sympatric, genetic entities which comprise what has been called Salsola tragus. Recent publications have referred to these as Salsola tragus and Salsola ‘type B’. Continued biocontrol efforts required the identification and characterization of ‘type B’. In the process, a third form was recognized and called ‘type C’. We examined Salsola tragus and Salsola ‘type B’ using morphometrics and ‘type C’ using DNA sequence data and morphometrics. Salsola tragus and ‘type B’ were morphologically distinct; ‘type C’ was morphologically intermediate between them and contained a combination of DNA sequence haplotypes mostly exclusive to S. tragus and exclusive to ‘type B’. We present a taxonomic and morphological characterization of Salsola tragus, Salsola ‘type B’ and ‘type C’ using discriminant analysis with DNA sequence genotypes as its taxonomic framework. We provide a pre-existing name, Salsola australis R. Br. for ‘type B’ and propose Salsola ryanii sp. nov. for ‘type C’. Morphological variation, habitats and dispersal behaviors among these Salsola taxa were examined in the herbarium and in the field. These are compared and discussed from both ecological and biocontrol viewpoints.

Fred Hrusa's Crosswalk

Scientist:
Dr. Fred Hrusa

This is an interface to the 2005 version of the nomenclatural crosswalk compiled by Dr. Fred Hrusa. The crosswalk is a database that accounts for the application of names of California plants. For the most part, The Jepson Manual of 1993 is the source of accepted names. The crosswalk is Dr. Hrusa's attempt to determine the Jepson name for names occurring in previous literature.

The crosswalk is neither exhaustive nor peer-reviewed (yet). It is made available by Dr. Hrusa with the hope that it will facilitate understanding of nomenclature of California plants.

CalFlora G.F. Hrusa Checklists

Scientist:
Dr. Fred Hrusa

This dataset of nearly 30,000 records is a collection of checklists from various authors, transcribed by Fred Hrusa as an ongoing project. The collection currently includes checklists for 126 locations around the state, with dates ranging from 1927 to 2005. As well as transcribing species lists and location information, Dr. Hrusa has evaluated documentation level and ID reliability, as well as brought older scientific names into a current nomenclatural usage. The individual checklists exist in hard copy form at various locations.

The data from this source can be searched via CalFlora by selecting the Data Contributor as "G.F. Hrusa Checklists" from the drop-down menu. Additional weed data from the CDFA Herbarium were also made available by Dr. Hrusa's contributions to CalFlora, and can be searched via CalFlora by selecting the Data Contributor as "California Department of Food and Agriculture" from the drop-down menu.

CDFA rated weeds location database

Scientist:
Dr. Fred Hrusa

Will be served here in the near future.