Thomas Nuttall

Abstract Trichomes are diverse and functionally important plant structures that vary in response to selection pressures across ecological gradients and evolutionary timescales. Classic hypotheses predict higher investment in trichomes in arid environments, at lower latitudes, and in long-lived species, as well as shifts in trichome production to reduce conflict between defense traits and mutualisms. However, tests of these hypotheses often rely on aggregate trichome metrics and neglect the rich diversity of trichome phenotypes. Here, we collected data on fine-scale patterns of trichome length, density, and type in 52 species of blazingstars (Mentzelia: Loasaceae) and tested whether individual trichome traits were consistent with existing adaptive hypotheses. Contrary to longstanding hypotheses, we found that Mentzelia species tend to display greater trichome investment in less arid environments and at higher latitudes. Barbed trichomes are significantly less common on the upper surface of the leaf, possibly reducing defense-pollination conflict. Species with larger petals (a proxy for reliance on insect pollinators) also shift investment away from insect-trapping hairs on the underside of the leaf. Examining trichome types separately revealed that different morphologies show distinct responses to abiotic and biotic factors, demonstrating the need to consider multiple axes of diversity when testing adaptive hypotheses for complex traits.

AbstractPremiseBiotic disjunctions have attracted scientific attention for the past 200 years. Despite being represented in many familiar plants (such as bald cypress, flowering dogwood, sweetgum, partridgeberry, etc.), the eastern North American (ENA)–Mexican (M) disjunction remains poorly understood. Major outstanding questions include the divergence times of taxa exhibiting the disjunction and environmental/geological processes that may underlie the disjunction. Symphyotrichum Nees (Asteraceae), one of the most diverse genera in the eastern USA, displays several examples of disjunct ENA–M taxa.MethodsWe generated target capture data using the Angiosperms353 baitset and generated the first well‐sampled phylogenomic hypothesis for Symphyotrichum and its close relatives. Focusing on S. subgenus Virgulus, we used MCMCTREE to perform divergence time estimation and the R package BioGeoBEARS to infer ancestral regions and biogeographic transitions between North America and Mexico. Finally, we used the ancestral niche reconstruction method Utremi to test for a role of historical aridification in generating the disjunction.ResultsOur molecular data suggest a recent radiation of Symphyotrichum at the Plio‐Pleistocene boundary (~2.5 mya), with early connections to Mexico in ancestral lineages that closed off shortly after and were followed by vicariance across this region. Except for some present‐day broadly distributed species, there is a complete lack of movement between ENA and M after ~0.5 mya.ConclusionsA reconstructed disjunct distribution of suitable habitat in Pleistocene climatic models corroborates results from biogeographic modeling and confirms glacial cycles are more likely to be associated with the breakup of ENA–M biogeographic connections.

Distributions of plants are expected to change in response to climate change, but the relative probability of that change is often unknown. Curl-leaf mountain mahogany (Cercocarpus ledifolius), an important browse species used by ungulates as forage and cover across the western US, is thought to be moderately to highly vulnerable to climate change this century, and a reduction in curl-leaf mountain mahogany occurrence may negatively impact ungulates reliant upon it. A combination of probability density estimation and vector analysis was used to predict curl-leaf mountain mahogany distribution across the species range relative to climate space and how that relationship would affect curl-leaf mountain mahogany at a local scale. Locally, we used the curl-leaf mountain mahogany population at the Bighorn Canyon National Recreation Area (BICA) in Montana and Wyoming for comparison. We modeled the probability of curl-leaf mountain mahogany occurrence across its distribution using water balance data to spatially and temporally assess the vulnerability of a population at a local scale. Modeled probabilities of occurrence and vector analysis indicated the species to remain in some areas within BICA but will be vulnerable in others given the predicted changes in temperature and precipitation in BICA if historical trajectories continue. This information allows managers to direct limited resources to other management actions by using the best available science to inform decisions. Other curl-leaf mountain mahogany populations currently inhabiting wetter, drier sites may follow a similar trajectory as the effects of climate change manifest. The approach used serves as a model to assess the predicted trend for species-specific plant communities of concern that may be adversely affected by climate change.

The Pan‐Himalaya, known as the “Roof of the World”, forms a natural geographic unit covering the entire range of the Himalaya and the Hengduan Mountains in addition to Karakorum and the northeastern extreme of Hindu Kush. The region possesses three biodiversity hotspots and harbors a rich and distinctive flora. Here, we review the history of plant diversity surveys and monographic studies in the region. The contributions of outstanding collectors of Pan‐Himalaya are also reviewed, as well as the ongoing international project on the Flora of Pan‐Himalaya (FPH). As the main concern of the present review, we showed that the development of botanic survey is uneven among different areas in the Pan‐Himalaya region, and that a special concern should be given to northern Myanmar and Yarlung Zangbo–Brahmaputra.

Before European contact, natural grasslands covered relatively little of Hawai‘i, with a grass flora composed of ∼48 species including 40 endemics. Following the proliferation of cattle ranches after the Great Mahele (land division) in the 1840s, it was quickly realized that the native grasses were not suitable for high intensity grazing. This sparked the importation of “improved” pasture grasses and set the path toward the contemporary dominance of foreign grasses across Hawai‘i. The importation of foreign grasses for forage accelerated dramatically in the early 1900s with the establishment of the Hawai‘i Agriculture Experiment Station (HAES) on O‘ahu by the United States government. The HAES imported seed, trialed grasses in introduction gardens, and distributed seed to ranchers across the islands. I performed a systematic review of literature produced by the HAES and similar organizations, newspapers, herbarium specimens, and floristic treatments to compile a record for the timeline of grass introductions, provide detailed historical context surrounding the introduction of these grasses, and reassess the status of species of controversial nativity. In total, 577 grasses were introduced post-1778, 158 of which were likely accidental introductions whereas 419 were deliberately imported. There are 232 species of grasses naturalized in Hawai‘i, including 102 deliberately introduced and 130 likely accidental. Deliberate introductions comprise the majority of invasive species which invade natural areas, whereas most accidental introductions are weeds associated with human disturbances. While deliberate introductions largely plateaued after 1970, new accidental introductions and some deliberate introductions with long lag periods continue to naturalize, with 30 newly naturalized grass species recorded between 2000 and 2023.

To understand how and where biodiversity is threatened, it is imperative to build historical baselines that accurately characterize the present and past states of biodiversity across environments. Botanical collections provide important ecological, evolutionary, and biogeographic information on the diversity and distributions of plant taxa, yet biases in collection efforts across spatial, temporal, and taxonomic scales are well known. Here, we characterize and quantify trends in botanical collections made from across different abiotic, biotic, and sociopolitical boundaries within the present‐day state of New Mexico. Using a biodiversity informatics approach applied toward a regional case study, we identify opportunities for efficiently improving natural history collection coverage and analyses of botanical diversity. Accurate representation of botanical biodiversity, preserved for future generations through vouchered plant specimens deposited in herbaria, depends on collection decisions made now. This work aims to provide a useful workflow for synthesizing digitized regional botanical collections as researchers prioritize current and future resources in the face of global change.

Globally, vector‐borne diseases are increasing in distribution and frequency, affecting humans, domestic animals, and wildlife. Science‐based management and prevention of these diseases requires a sound understanding of the distribution and environmental requirements of the vectors and hosts involved in disease transmission. Integrated Species Distribution Models (ISDM) account for diverse data types through hierarchical modeling and represent a significant advancement in species distribution modeling. We assessed the distribution of the soft tick subspecies Ornithodoros turicata americanus. This tick species is a potential vector of African swine fever virus (ASFV), a pathogen responsible for an ongoing global epizootic that threatens agroindustry worldwide. Given the novelty of this method, we compared the results to a conventional Maxent SDM and validated the results through data partitioning. Our input for the model consisted of systematically collected detection data from 591 sampled field sites and 12 historical species records, as well as four variables describing climatic and soil characteristics. We found that a combination of climatic variables describing seasonality and temperature extremes, along with the amount of sand in the soil, determined the predicted intensity of occurrence of this tick species. When projected in geographic space, this distribution model predicted 62% of Florida as suitable habitat for this tick species. The ISDM presented a higher TSS and AUC than the Maxent conventional model, while sensitivity was similar between both models. Our case example shows the utility of ISDMs in disease ecology studies and highlights the broad range of geographic suitability for this important disease vector. These results provide important foundational information to inform future risk assessment work for tick‐borne relapsing fever surveillance and potential ASF introduction and maintenance in the United States.

AbstractPremiseClines—or the geographic sorting of phenotypes across continual space—provide an opportunity to understand the interaction of dispersal, selection, and history in structuring polymorphisms.MethodsIn this study, we combine field‐sampling, genetics, climatic analyses, and machine learning to understand a flower color polymorphism in the wide‐ranging desert annual Encelia farinosa.ResultsWe find evidence for replicated transitions in disk floret color from brown to yellow across spatial scales, with the most prominent cline stretching ~100 km from southwestern United States into México. Because population structure across the cline is minimal, selection is more likely than drift to have an important role in determining cline width.ConclusionsGiven that the cline aligns with a climatic transition but there is no evidence for pollinator preference for flower color, we hypothesize that floret color likely varies as a function of climatic conditions.

Premise Cleomaceae is an important model clade for studies of evolutionary processes including genome evolution, floral form diversification, and photosynthetic pathway evolution. Diversification and divergence patterns in Cleomaceae remain tangled as research has been restricted by its worldwide distribution, limited genetic sampling and species coverage, and a lack of definitive fossil calibration points.MethodsWe used target sequence capture and the Angiosperms353 probe set to perform a phylogenetic study of Cleomaceae. We estimated divergence times and biogeographic analyses to explore the origin and diversification of the family. Seed morphology across extant taxa was documented with multifocal image‐stacking techniques and morphological characters were extracted, analyzed, and compared to fossil records.ResultsWe recovered a well‐supported and resolved phylogenetic tree of Cleomaceae generic relationships that includes 236 (~86%) species. We identified 11 principal clades and confidently placed Cleomella as sister to the rest of the family. Our analyses suggested that Cleomaceae and Brassicaceae diverged ~56 mya, and Cleomaceae began to diversify ~53 mya in the Palearctic and Africa. Multiple transatlantic disjunct distributions were identified. Seeds were imaged from 218 (~80%) species in the family and compared to all known fossil species.ConclusionsOur results represent the most comprehensive phylogenetic study of Cleomaceae to date. We identified transatlantic disjunctions and proposed explanations for these patterns, most likely either long‐distance dispersals or contractions in latitudinal distributions caused by climate change over geological timescales. We found that seed morphology varied considerably but mostly mirrored generic relationships.

Background: The genus Pinguicula harbors 110 species, of which 53 are distributed in Mexico. The formation of the Mexican mountains has favored the Pinguicula diversification. Pinguicula specimens collected in the State of México, along the Trans-Mexican Volcanic Belt (TMVB) do not correspond with any known species. Questions: Do the collected specimens belong to a new species? What is its conservation status? How many Pinguicula species are there along the TMVB and how do they differentiate? How is the Pinguicula species richness distributed? Studied species: Pinguicula. Study site and dates: TMVB, 2005-2023. Methods: Based on herbarium specimens and recently collected material, a morphological analysis and description were made. Conservation status was assessed following IUCN Red List Categories and Criteria. Herbarium specimens and digital records of Pinguicula from the TMVB were examined to generate a list and key. We analyzed the richness distribution of Pinguicula by states, vegetation types, elevation ranges, and grid cells. Results: Pinguicula tlahuica is proposed as a new species. It is distinguished by the linear-spatulate summer leaves. The new species falls into the Endangered (EN) category. Along the TMVB, 16 species of Pinguicula are distributed. The State of México, Hidalgo and Michoacán, and the pine-oak forest were the richest. Pinguicula appeared between 759-3,427 m asl. The grid cell analyses revealed different areas with high richness. Conclusions: Along the TMVB, the Pinguicula species richness centered on the Eastern and Western sectors. Pinguicula crassifolia, P. michoacana, P. tlahuica, and P. zamudioana are endemic to the TMVB.