An identifying feature of Quercus agrifolia Née (Fagaceae) is the presence of hair tufts on lower leaf surfaces. In other plant species, hair tufts act as domatia for arthropods such as mites, which in turn feed on leaf fungi or small herbivores and possibly benefit plant health. However, this mutualistic relationship remains untested in Q. agrifolia. In this study two primary questions were addressed within a natural stand of Q. agrifolia in San Luis Obispo, CA: 1) Do hair tufts act as domatia for mites? and 2) Does the removal of hair tufts impact mite abundance, herbivory or fungal pathogens on leaves? In an observational study of 377 leaves from 20 trees, we found a significant association between the presence of hair tufts and the presence of mites. When we experimentally removed hair tufts, we found a significant reduction in mites, yet there was no impact on leaf herbivory or necrosis. We conclude leaf hair tufts on Q. agrifolia serve as domatia for mites, but we found no evidence that mites reduce herbivory or fungal pathogens. Thus, while mites likely benefit from housing provided by hair tufts on Q. agrifolia, it is unclear that the tree benefits from the mites, i.e., whether this is a mutually beneficial relationship.

Results from molecular phylogenetic analyses have indicated that the two southernmost species in Mentzelia section Bicuspidaria, M. hirsutissima sensu lato and M. involucrata, form a clade in which M. hirsutissima is paraphyletic with respect to M. involucrata. Here we elevate M. hirsutissima S.Watson var. nesiotes I.M.Johnst. to specific rank, recognizing it as M. nesiotes (I.M.Johnst.) Brokaw & J.J.Schenk, thus rendering all three taxa monophyletic. Mentzelia nesiotes is allopatric relative to M. involucrata and M. hirsutissima sensu stricto, with all known populations of M. nesiotes occurring in northern Baja California Sur and nearby Pacific islands. Multivariate analyses of morphological differences determined that M. nesiotes and M. hirsutissima are best distinguished by capsule length, calyx length, and leaf intersinus width. Estimation of climate niches with MaxEnt inferred that M. nesiotes and M. hirsutissima showed minimal overlap in climate tolerances, with M. nesiotes inhabiting the Vizcaíno fog desert west of the Peninsular Ranges and M. hirsutissima inhabiting areas further north with higher precipitation and temperature fluctuations primarily east of the Peninsular Ranges. We provide updated circumscriptions of all three species, reduce M. hirsutissima var. stenophylla and M. involucrata var. megalantha to synonymy with their respective species, and designate the lectotype of M. hirsutissima.

A population of Vaccinium from San Bruno Mountain in San Mateo County, California has been confused with V. cespitosum Michx. (V. sect. Myrtillus), a species documented from the mountain, since its initial collection in 1961. These plants resemble V. cespitosum and other species in V. sect. Myrtillus in several characters, but differ most notably in their evergreen habit and well developed calyx lobes. The latter characters are shared by V. ovatum Pursh (V. sect. Pyxothamnus), the only other species of Vaccinium known from San Bruno Mountain, suggesting that the population is a hybrid between V. cespitosum and V. ovatum. We used data from gross morphology, leaf anatomy, and DNA sequences from the nuclear ribosomal internal transcribed spacer (ITS) and plastid matK and ndhF regions to test the hybrid status of this population. Hybrid status is supported by: 1) a plastid sequence profile identical to that of V. cespitosum from San Bruno Mountain and different from the profiles of all other Vaccinium samples in the study, 2) an ITS profile that differs from V. cespitosum from the mountain by only two polymorphic sites, and 3) the possession of gross morphological and anatomical characters that are either shared with one putative parent or the other, or are intermediate between them. Although ITS variation was non-additive and closely matched one of the putative parents, uniparental inheritance has been observed in other hybrids. Two novel gross morphological characters were also observed in the hybrid. The study documents a case of likely intersectional hybridization within Vaccinium, only rarely observed under natural conditions. Vaccinium cespitosum may have been outcompeted by the hybrid to the point of its extirpation from San Bruno Mountain. The population is here newly described as the nothospecies Vaccinium ×brunoense P.W.Fritsch, occurring in an area of only ca. 200 m² with the number of individuals remaining uncertain because of clonal growth.

Astragalus tricarinatus A.Gray (triple-ribbed milkvetch) is a rare perennial herb endemic to southern California and is listed as endangered under the Federal Endangered Species Act. Field surveys conducted between 2014 and 2017 relocated A. tricarinatus at one of three historical occurrences in the southern portion of its range in Riverside County, California. Surveys in the Chuckwalla Mountains and Orocopia Mountains were not successful in relocating historical occurrences; however, new occurrences were documented in the Santa Rosa Mountains. Plants in the Santa Rosa Mountains were growing on carbonate soils, a substrate that had not been previously associated with A. tricarinatus, which typically occurs on metamorphic rock of granitic origin.

The ability of plants to tolerate and recover from periodic water stress affects their competitive ability, survival, and distribution, leading to shifts in plant communities as environmental conditions change. We investigated the hydraulic traits of two closely related Pinus taxa to assess population and taxonomic variability in plant hydraulic traits. We hypothesized that traits would vary with elevation but exhibit similar traits where taxa co-occurred. We measured predawn and midday leaf pressure potential (Ψ_p) across three seasons, xylem specific hydraulic conductivity (K_s), and vulnerability to xylem embolism (P₅₀). These were measured on Pinus ponderosa var. brachyptera (Engelm.) Lemmon that occurred at a high elevation site (2770 m), P. arizonica Engelm. at a low elevation site (2135 m), and both species where they co-occurred at the mid-elevation site (2475 m) in the Santa Catalina Mountains of southern Arizona. Plants from the high elevation site had the least negative Ψ_p and the highest K_s. The two taxa differed from one another when compared between the high and low elevation sites, but they were not different where they co-occurred. The two Pinus taxa show plasticity in their hydraulic traits across sites. Conditions across the elevational gradient appear to lead to a convergent solution in hydraulic traits for these taxa where their ranges overlap but differences in traits where they do not overlap. Increasing aridity in the region could lead to shifts in suitable habitat, reduced water transport ability at range margins, and shifts in population distributions.