The San Francisco Volcanic Field lies near the southern edge of the Colorado Plateau in north-central Arizona, and is dominated by an extensive Pinyon-Juniper woodland. During 2004 and 2005, a floristic inventory vouchered 487 taxa from 74 families and 268 genera, including eight species endemic to Arizona. The Asteraceae, Poaceae, Fabaceae, Brassicaceae, and Scrophulariaceae comprised 51% of the total flora. Eriogonum, Muhlenbergia, Penstemon, Aristida, Astragalus, and Cryptantha were the best represented genera. Nonnative taxa accounted for ten percent of the total flora. Cryptantha minima and Suckleya suckleyana were vouchered as new records for Arizona.

A long-term history of water table fluctuations, from alternating periods of drought and abundant precipitation, can be preserved in the stratigraphy of wetland sediments. We examined the middle to late Holocene history of vegetation and climate change from a small wetland on the Modoc Plateau in Shasta County, northeastern California. This site is at a transition between the Great Basin and the Californian Floristic Provinces, and the paleoecological record from Flycatcher Basin exhibits affinities to both. Although the sedimentary record extends back to ca. 8300 cal yr BP, organic sediment did not form until ca. 4500 cal yr BP, indicating that water was probably absent in the basin during the middle Holocene. Pollen and plant macrofossils deposited after 4500 cal yr BP suggests a mixed conifer – Quercus forest grew around Flycatcher Basin. Charcoal is abundant in these sediments, indicating periodic forest fire. Distinctly modern forests developed by about 2200 cal yr BP, when Pinus became the dominant conifer with Quercus, in a more closed forest, perhaps with more frequent fire. The record from Flycatcher Basin provides no evidence for change in the boundaries between the Great Basin and California (Cascadian) floristic provinces during the period of record. The late Holocene is interpreted as a generally increasingly mesic sequence, with a long-term increase in groundwater recharge, yet interspersed by extended drought during the last 2000 yr. Extended droughts occurred from ca. 1125 AD to 1450 AD, with an earlier protracted dry period from ca. 100 AD to ca. 900 AD. Generally wetter periods occur from ca. 1000 to 1125 AD, and after ca. 1450 AD. The paleoenvironmental changes in the Flycatcher Basin wetland are a local expression of a much broader climatic pattern, as shown by several studies of higher resolution proxies. The record from Flycatcher Basin wetland is important in demonstrating the centennial to millennial-scale fluctuations in water availability in a region of rapidly expanding human population, with an increasing need for water resources.

Plant communities in the southern Coast Range of California form a mosaic with discrete to gradual transitions between multiple vegetation types. To accurately portray this pattern and to quantify the areal coverage of ecotonal space, a new method of mapping vegetation was developed. Vegetation stands were classified and mapped in separate GIS layers to the full extent of their respective suite of indicator species. Since all stands were mapped in this way, the overlap of different communities in the GIS represents ecotonal space. Vegetation mapping was entirely ground-based using a GPS receiver. Vegetation classification followed the Holland and Keil scheme. Eleven plant communities were identified within the 92.6 ha study area. This mapping method revealed that 32% of the total area was ecotonal and that the majority of plant communities exhibited a greater portion of their total area as ecotone than as discrete space. This finding suggests that typical vegetation maps depicting discrete boundaries between all vegetation types may misrepresent a nontrivial proportion of the area mapped. In addition, because ecotones are ecologically significant and important to conservation, the portrayal of transitional space between communities is worth consideration in the future creation of vegetation maps within California.

Mount Pinos at the western margin of the Transverse Ranges of Southern California. reaches 2692 m in elevation at its peak. The broad summit of the mountain supports an area of subalpine fellfield vegetation, as well as an unusual low elevation occurrence of limber pine (Pinus flexilis). We describe the summit area of the mountain and characterize the community structure and ecophysiology of the fellfield community and associated pines. The fellfield community, dominated by low mats and cushions of Eriogonum kennedyi, Phlox diffusa, and Lupinus breweri var. bryoides, has a mean plant cover of 44%. These fellfield species have amphistomatic leaves with abundant, slender palisade cells on both sides of the mesophyll. These traits represent a strategy shared with desert plants. Amphistomaty helps to increase assimilation by maximizing stomatal conductance to CO₂ during the gas phase of diffusion, and the isolateral mesophyll maximizes diffusion of CO₂ by exposing a very high mesophyll membrane area per leaf surface area. However, the mean maximum rates of assimilation measured for Phlox diffusa, Eriogonum kennedyi, Astragalus purshhii var. tinctus, and Lupinus breweri var. bryoides were 6.8 to 13.9 µmol CO₂ m⁻² s⁻¹, placing them in the lower range of those measured in alpine areas of the world.

Euphorbia terracina L., also known as terracina spurge, is a Mediterranean Basin perennial that has recently become invasive in southern California and is actively spreading at a virtually exponential rate along coastal areas in Los Angeles County. The National Park Service (NPS) is undertaking measures to treat and control further spread of current populations, but little is known about the plant's ecology and impact on native plant communities. This study reviewed the existing information on E. terracina and investigated populations established in Solstice Canyon in coastal Los Angeles County. Populations of E. terracina were compared in two different habitats in Solstice Canyon: in an open site along an old road and a shaded riparian site subject to past disturbance. Both open-disturbed and shaded sites had high aboveground biomass densities, with the highest density in the open, disturbed site. Sites differed in biomass allocation and specific leaf area (SLA) between sites, with plants at the open site having significantly lower specific leaf area than those at the shaded site. Open site plants also had high SLA compared to native coastal sage scrub species. Euphorbia terracina produces large quantities of seeds that do not show dormancy. Seeds germinated well under low light intensities without mechanical or chemical treatment. Euphorbia terracina possesses numerous traits — success in disturbed sites, phenotypic plasticity, high SLA compared to native species, high reproductive output, and seeds lacking dormancy — that have been associated with invasive species and likely contribute to both its success and the difficulty in treatment and control of established populations.

Dissanthelium californicum (Nutt.) Benth. (Poaceae) is an annual grass known only from Santa Catalina and San Clemente Islands, off the coast of Southern California, USA, and Guadalupe Island, off the coast of Baja California, Mexico. It had not been recorded since Blanche Trask collected it in 1903 on San Clemente Island, and was therefore considered to be extinct, possibly as a result of overgrazing by introduced goats on these islands. During monitoring by the Catalina Island Conservancy from March through July 2005, D. californicum was discovered growing in seven diverse and widely spread locations on Santa Catalina Island. The rediscovery may be a result of the removal of feral goats and pigs from the island, record-breaking rainfall, and increased exploration of remote areas. A revised description of the species and a summary of its habitat preferences are provided. Thorough monitoring and surveying of known and potential locations will be necessary to better determine the conservation status of the species.

Relocation and further study of the local endemic Asclepias zacatecana McVaugh showed that it is conspecific with A. schaffneri A. Gray, a distinct species that previously had been synonymized with A. quinquedentata A. Gray. However, we consider a recently described species, A. rzedowskii W.D. Stevens, to be conspecific with A. quinquedentata. Asclepias schaffneri is lectotypified.

Cryptantha crinita Greene (silky cryptantha) is a rare native annual plant previously known solely from alluvial soils of the northern Sacramento Valley in California. It has been considered a lowland species (85–300 m) associated with creekbeds. Several recent collections (1990–2004) made in upland habitats at 850–1200 m show that the species is more common and has a wider ecological amplitude than previously thought. Although the habitats of the upland and valley sites differ, they are both characterized by a sparse vegetative cover which appears to be a key factor for establishment and growth of C. crinita.

A new species, Eriastrum signatum D. Gowen, is described for most plants previously identified as E. sparsiflorum, and a new combination, E. harwoodii (T. T. Craig) D. Gowen, is proposed for densely woolly plants having apiculate corolla lobes found in the eastern Mojave Desert. Additionally, both E. sparsiflorum and E. tracyi are discussed, and a key to Eriastrum with small stamens is provided.

Eriastrum sparsiflorum is a minutely glandular-pubescent annual plant limited to small areas in the southern Sierra Nevada, and along the eastern base of the Sierra in California and western Nevada. Eriastrum sparsiflorum has been misapplied to Eriastrum signatum and E. tracyi. Eriastrum signatum ranges from Oregon to southern California and western Nevada, and differs from E. sparsiflorum by having a dark maroon colored spot at the base of the corolla lobes and lacking glandular hairs. Eriastrum tracyi, which is presently placed in synonomy under E. brandegeeae, warrants recognition as a distinct taxon. It occurs on coastal ranges of California, the western edge of the Modoc Plateau in northeastern Shasta County, as well as the southwestern Sierra Nevada.