Dudley's Lousewort (Pedicularis dudleyi Elmer) is a rare and apparently declining species confined to two populations associated with Redwood forests in coastal California. In this study, we aimed to determine whether pollination, seed dispersal, or seed germination were important limiting factors for population growth of P. dudleyi at Portola Redwoods State Park, the northernmost of the two known populations. We conducted a full census of the population, performed pollinator and seed disperser observations, conducted a pollinator exclusion study, and conducted a litter removal experiment and a greenhouse seed germination study. Fewer than 500 reproductive individuals were found in the census, confirming the extremely small population size at the State Park. Both pollination by native bees (Bombus spp. Latreille 1802) and seed dispersal by yellowjackets (Vespula alascensis Packard 1870) appear to be robust. The litter removal results were inconclusive and no seeds successfully germinated. Combining age class data from the census, poor overall recruitment in the litter removal trial, and poor seed germination, we infer that low establishment of new individuals and populations is a primary threat to the species and should be the focus of future management goals.

Phacelia stebbinsii Constance & Heckerd, P. marcescens Eastw. ex J.F.Macbr., and P. quickii J.T.Howell are morphologically similar annual taxa endemic to the west side of the Sierra Nevada in California. Experimental crosses show P. quickii is reproductively isolated from the other two species, and that P. marcescens and P. stebbinsii readily produce fully fertile F₁ and S₂ hybrid progeny, but typically only when P. marcescens is the carpellate parent. The presence of geographic separation, habitat differences, unilateral crossability, pollen certation, and problems with cotyledon emergence in hybrid seedlings provide evidence P. stebbinsii is distinct from P. marcescens and they are maintained as separate species. Flower and fruit characters used to distinguish these three species from each other appear to be related to differences in seed dispersal and seedling establishment in different habitats.

Rio Grande Butterfly Bush, Buddleja sessiliflora Kunth (Scrophulariaceae), reaches its northernmost distribution in southeast Arizona, and herbarium records document seven historical localities from Pima and Santa Cruz counties. Between 2014–2020, we visited six of the documented historical localities, but could not access the seventh location reported from the Tohono O'odham Nation. We found one of these historical locations is no longer extant. Two recently discovered new sites were also visited. We verified a total of 30 plants, in nine populations, from seven distinct localities during this research, which included the two previously unknown sites. Five of the seven localities were restricted to 6–15 m diameter areas and contained between one and seven plants, while the other two localities each included two disjunct 5 m diameter clusters of plants. We only found two small plants, which are likely seedlings or propagules. It is unclear why these plants rarely reproduce in situ, either sexually or vegetatively. These isolated riparian populations experience environmental stress, including hotter drought, diminishing water resources, anthropogenic habitat disturbance, and invasive plant species. This study resulted in an Arizona state designation for B. sessiliflora of ‘S1: critically imperiled.’ Buddleja sessiliflora may be one of the rarest plants in southern Arizona, and these peripheral populations face an increased extirpation risk.

California, a hotspot of plant biodiversity, is projected to experience a significant increase in average temperature by the end of the century, from +1.5°C under low emissions to +4°C under medium-high emissions models. This warming could severely affect unique, endemic ecosystems like the chaparral. Phenotypic plasticity, the capacity of organisms to express different phenotypes in response to environmental cues, may be an important means by which plants adjust to climate change. Here, we examine differentiation in two traits related to climate adaptation, leaf length and trichome density, previously observed to differ qualitatively between coastal and inland populations of Eriogonum fasciculatum subsp. foliolosum (Nutt.) S.Stokes. We quantitatively verify these leaf trait differences, assess whether they are plastic to temperature, and also assess whether coastal and inland populations express this plasticity differently. We performed field collections, established a novel procedure for vegetative propagation of woody cuttings, and grew cuttings and germinated seeds in temperature treatments simulating current conditions and those projected by future climate models. Our results revealed that leaf traits of both populations respond plastically to temperature, and we also found differentiation for the plasticity expressed by the two populations. Population genetic analyses detected limited genetic differentiation and high gene flow between these two populations, indicating that the observed differentiation in plasticity may be locally adaptive. Together, these findings suggest that this system may exemplify genetic accommodation, in which the evolution of plasticity mediates adaptation, and imply that variation in plasticity is relevant to conservation strategies for this plant and other California native chaparral shrubs in the face of climate change.

Pollen morphology is species-specific and its identification can inform many different research objectives, including those focused on understanding pollinator niche breadth, pollen transfer dynamics, and factors driving plant community composition. Community-wide characterization of pollen can thus accelerate research on plant-pollinator interactions on both contemporary and historical time frames. Here we present descriptions, a dichotomous key, and reference set of light microscopy images of pollen from 70 species in 28 families of co-flowering plants growing in and around serpentine seeps at the McLaughlin Natural Reserve in Lake County, CA. This represents a reference and a tool for the study of species interactions in this unique biodiversity hotspot.

There are three species in the genus Fremontodendron in California, two of which are rare, narrowly distributed endemics. Of the three, F. californicum (Torr.) Coville is the most widely distributed. It is a facultative resprouter with dormant seeds stimulated to germinate by fire. In this study I monitored post-fire densities, mortality, and heights of F. californicum seedlings for four years after a stand-replacing fire in a Pinus monophylla Torr. & Frém. forest. Thousands of F. californicum seedlings established in the first-year post-fire. Initially, most germinated in seedling clumps rather than as single seedlings. Those establishing under resprouting shrubs consistently had higher densities, but generally were shorter than seedlings in transects. Camera trapping at two study sites revealed that Ammospermophilus leucurus (Merriam 1889), Dipodomys merriami (Mearns 1890), and Peromyscus truei (Shufeldt 1885) removed F. californicum seeds under shrubs and probably cached many of them. Caching rodents likely play a major role in the seed dispersal of F. californicum in the interval between fires, as suggested by the clumped distribution of seedlings. The ant Pogonomyrmex subnitidus (Emery 1895) removed seeds from beneath shrubs at the unburned site, but not in the burn area. Shrubs at both sites produced fruits that released seeds slowly. Even after a year, small numbers of seeds remained at the bottom of fruit locules in the canopy and on the ground. Only small mammals open fruits and remove seeds from the bottoms of locules.

The use of mechanical thinning as a restoration tool in second-growth Sequoia sempervirens (D.Don) Endl. forests is becoming increasingly common, yet little is known about how this treatment affects understory plant communities. The shade tolerant herbaceous species common to the Coast Redwood forest are known to be sensitive to disturbance and may provide a metric for assessing the recovery of the plant community as a whole. Stratified random sampling was used to compare understory composition in old-growth reference stands, naturally recovering forests (57–65 years old), and sites treated with variable density thinning (65 years old; 10–12 years post thinning) in Redwood National Park. Pairwise permutational multivariate analysis of variance (PerMANOVA) indicated greater abundance of native herbs, and lower abundance of non-natives, in old-growth and naturally recovering second-growth compared to thinned stands. Non-metric multidimensional scaling suggested that un-thinned sites were more similar to old-growth than thinned sites in regard to understory composition and abundance, and indicator species analysis returned a suite of indicator species shared between naturally recovering plots and old-growth plots (Pteridium aquilinum (L.) Kuhn; Trillium ovatum Pursh; Dryopteris arguta (Kaulf.) Maxon; Blechnum spicant (L.) Roth; Vaccinium ovatum Pursh; Gaultheria shallon Pursh; Rubus spectabilis Pursh; Rhododendron macrophyllum D.Don ex G.Don), while thinned plots shared only one indicator species with old-growth (Goodyera oblongifolia Raf.). In addition, both old-growth and naturally recovering un-thinned second-growth sites were dominated by residual species, while thinned plots were dominated by invader species.

As wildfires increase in extent and intensity and threaten local communities, active suppression tactics are becoming more common, including the creation of fire lines. Post-fire, these sites can become populated with non-native species and risk type conversion if native species recovery is lacking. Minimal research exists on the plant community trajectory of these mechanically disturbed sites. We studied the 32-Fire located east of Chico, CA. A fire line approximately 0.5 km long ranging in width from 6–12.2 m was created by a bulldozer. To assess plant recovery, we established plots in three pre-fire vegetation types: California Black Oak (Quercus kelloggii Newb.), Manzanita (Arctostaphylos manzanita Parry), and Wedgeleaf Ceanothus (Ceanothus cuneatus [Hook.] Nutt.) within three disturbance levels: burned, unburned (reference), and disturbed dozer line. Sites were sampled in 2018 (six-months post-fire) and in 2019 (18-months post-fire). In 2019, dozer line sites in the Manzanita and Wedgeleaf Ceanothus vegetation types did not have the dominant species found in similar unburned or burned sites. Across all vegetation types, dozer line sites had significantly higher average percent non-native species cover, compared with respective burned (P < 0.001, 95% C.I. = 33.2, 64.8) and unburned areas (P < 0.001, 95% C.I. = -77.2, -45.5). While unburned Wedgeleaf sites average non-native cover was 11% (SD = 9) in 2018 and 20% (SD = 5) in 2019, Wedgeleaf dozer line sites average non-native cover remained high between survey years at approximately 85%. Manzanita dozer line sites had average nonnative cover of 76% (SD = 16) and 57% (SD = 25) in 2018 and 2019, respectively, while unburned Manzanita had 9% (SD = 9) and 16% (SD = 16). Manzanita and Wedgeleaf Ceanothus species present on the study site are obligate seeders. Since neither species survived the implementation of the dozer line and no new recruitment of these species was observed, future recruitment of obligate seeders in these areas is unlikely. This suggests that dozer line sites with obligate seeders as dominant or co-dominant species are at risk of type conversion from native chaparral to annual grasslands dominated by non-native species.

A new white-rayed Layia, L. erubescens B.G.Baldwin, is described from the Central Coast of California. This species, previously not recognized as distinct from L. glandulosa (Hook.) Hook. & Arn., is evolutionarily and ecologically discrete, occurring in loose, fine sand of stabilized backdunes and sandhills from central San Luis Obispo to southern Santa Barbara counties. It differs from L. glandulosa and other members of Layia by the character-state combination of being strongly aromatic (resinous-spicy odor), with a central stem often strictly erect, proximal leaves often deeply lobed, sometimes with minor secondary lobes, ray corollas generally aging pink to rose, and pappus scales narrowly linear-attenuate, 0.8–0.13(0.19) mm wide. Previously published phylogenetic analyses indicated that L. erubescens is an evolutionary outlier to L. glandulosa in its newly restricted sense, which is more closely related to L. discoidea than to L. erubescens. Layia erubescens is declining and of major conservation concern as a result of habitat loss from development of coastal areas and aggressive invasion throughout its range by perennial veldt grass (Ehrharta calycina Sm.).

Allium incomptum J.A.Kierstead & L.Lindstrand III, sp. nov. (Alliaceae) is described as a new species of Allium from northern California. This new species is most similar to A. yosemitense Eastw., but differs by several features including its shorter pedicels, narrow, blunt tepals, and markedly exserted stamens, contrasted with the longer pedicels, acute tepals, and stamens not or barely exserted in A. yosemitense. The two species have widely disjunct geographic ranges in California, A. incomptum endemic to the eastern Klamath Ranges and A. yosemitense endemic to the central Sierra Nevada. We describe the morphological characters and habitat characteristics for A. incomptum, one in a series of recently discovered vascular plant taxa endemic to the eastern Klamath Ranges.

During the course of a floristic study of the Cal Poly Swanton Pacific Ranch, in Santa Cruz County, we observed and collected several specimens that keyed to Sanicula crassicaulis Poepp. ex. D.C. but were notably distinct from other S. crassicaulis that we collected in the area. On further investigation, we found that these plants match the type specimen of S. nudicaulis Hook & Arn., described in 1839 and later synonymized with S. crassicaulis. This taxon is distinguished primarily by its long, sinuate marginal leaf trichomes, in contrast to the short, straight marginal trichomes of S. crassicaulis. Additionally, the length of the most proximal prickles on the schizocarps is about the same as the length of the most distal rather than the distal prickles being much longer as in S. crassicaulis and the angle of attachment of the prickles is more or less perpendicular as opposed to acute in S. crassicaulis. The known range of this taxon is between the San Francisco Bay Area and Santa Barbara County, generally near the coast. Here we recognize this taxon as a variety in S. crassicaulis. We provide a diagnosis, a map of the known range of the taxon and a key to the varieties of S. crassicaulis in California.

Three new species of Cryptantha from the Channel Islands of southern California are described. Cryptantha clementina, endemic to San Clemente Island, was formerly identified as C. traskiae I.M.Johnst. It is distinct from that species in having a low, spreading growth habit, congested inflorescence cymules, wider corolla limbs, thicker and more swollen midrib calyx trichomes, and nutlets that are tuberculate throughout the dorsal and ventral surfaces. Cryptantha kinkiensis, also endemic to San Clemente Island, was previously identified as C. intermedia (A.Gray) Greene. It differs from that species in having bifurcate cymules and nutlets with denser, smaller tubercles. Cryptantha catalinensis, endemic to Santa Catalina Island, was previously identified as either C. intermedia or C. wigginsii I.M.Johnst. It differs from C. intermedia in having bifurcate cymules and nutlets with denser, smaller nutlet tubercles. It differs from C. wigginsii in having nutlets that are tuberculate apically and low-tuberculate to glabrate basally, as opposed to densely tuberculate apically (tubercles “wart-like” and generally abutted) and glabrous and shiny basally in C. wigginsii. Cryptantha catalinensis and C. kinkiensis are somewhat similar to one another, but distinct in nutlet sculpturing and midrib calyx trichome size. We note morphological similarities and some evidence for phylogenetic relatedness among Cryptantha clementina, C. traskiae, and C. foliosa (Greene) Greene, the last endemic to Guadalupe Island, Baja California, Mexico. We also point out morphological similarities among Cryptantha catalinensis, C. kinkiensis, and C. wigginsii. Detailed molecular phylogenetic studies are needed to evaluate the evolutionary and biogeographic history of these new insular species.