Publications

ABSTRACT

Abstract

In the USA, 944 plant taxa are listed as threatened or endangered under the Endangered Species Act. Brassicaceae is the fourth most threatened family with 41 listed species. This study focuses on slickspot peppergrass (Lepidium papilliferum), a threatened Brassicaceae endemic to south-western Idaho that is experiencing significant population decline and reduced fecundity. Our goal is to support the establishment of a breeding and genetic rescue programme to restore populations of this species by addressing the following objectives: (i) confirm its genomic origin, (ii) investigate the importance of ancestral hybridization on its origin, (iii) propose a phylogeographic hypothesis to inform its restoration, and (iv) offer conservation and restoration guidelines. We sampled 44 L. papilliferum individuals from 27 element occurrences (populations) across three landscape management regions, as well as 16 individuals from closely related species. Using Illumina sequencing, we assessed genome size and heterozygosity, and conducted phylogenetic and genetic clustering analyses on nuclear and plastome data. Results showed that L. papilliferum has an allopolyploid origin, with genome size variation and genotype frequencies supporting segmental allopolyploidization. Genomic discordance suggested the occurrence of ancestral hybridization events. Nuclear phylogenetic analysis confirmed the species’ monophyly, possibly because of genetic isolation driven by ecological speciation. We used genetic groups to redefine landscape management regions for the species, offering new boundaries for a forthcoming species recovery plan. This research provides essential genetic insights to inform the restoration of slickspot peppergrass populations and guide conservation efforts.

Global biodiversity policies recognize the necessity to preserve evolutionary lineages, as their diversity underpins current and future benefits to people and the future of life on Earth. Plants are largely absent from global biodiversity assessments, resulting in a taxonomic imbalance that has undermined their conservation for decades. We present a tree of life and extinction risk estimates for all species of flowering plants (angiosperms), representing a global assessment of their threatened evolutionary history. We estimate that 21.2% of angiosperm evolutionary history is at risk of extinction and identify 9945 priority species that disproportionately account for total threatened evolutionary history. These prioritizations serve to redress imbalances between plants and animals, monitor conservation effectiveness, and optimize resource allocation in the face of increasing human pressures on biodiversity.

Leaf traits are crucial to seedling growth and survival, and their plasticity can influence seedling fitness in changing environments. Seedlings of Artemisia tridentata, a keystone shrub of the western North American sagebrush steppe, show heteromorphic leaf development. Early leaves are larger and less pubescent than those produced later, suggesting a shift from characteristics favouring rapid growth to those increasing drought tolerance. To investigate this hypothesis, we determined the specific leaf area (SLA) and the osmotic potential at full turgor (π0) of early and late leaves, and measured their stomatal conductance and photosynthetic rates as leaf water potential (Ψl) declined under imposed drought. We also examined whether water stress could trigger late leaf development. At high Ψl and per area, early and late leaves had similar photosynthetic rates. However, the SLA of early leaves was three times higher than that of late leaves, yielding higher photosynthetic rates per unit mass in the former. Late leaves had lower π0 and were less sensitive to drought, exhibiting a lower Ψl at 50% of maximum photosynthesis than early leaves. Drought triggered the shedding of early leaves and the initiation of late-like leaves. Formation of these leaves continued upon return to well-watered conditions, possibly indicating stress memory. The overall results suggest that early leaves enhance growth during wet springs following germination, while late leaves prolong photosynthesis as water potentials decline during summer drought. The adaptive value of early leaves may be diminishing due to changing environmental conditions that are accelerating the onset of drought.

Premise

Pandanus Parkinson (Pandanaceae) is a large genus of paleotropical tree‐like monocots. Previous studies using small DNA regions questioned the monophyly of the seven Pandanus subgenera, but low phylogenetic branch support hindered further investigations. We aimed to (1) test Pandanus subgeneric monophyly, (2) identify clade morphological synapomorphies, (3) investigate correlations between leaf anatomy of water storage tissue and climatic differentiation across clades, and (4) construct hypotheses on the genus' spatiotemporal history.

With ca. 200 morphologically variable species placed in 20 putative genera within the tribe Selineae of subfamily Apioideae, the Perennial Endemic North American (PENA) clade of Apiaceae forms the second‐largest plant radiation entirely endemic to North America, yet, elucidating evolutionary relationships for this intractable plant lineage has been challenging. The objectives of this study are to elucidate the monophyly of the PENA clade and assess phylogenetic relationships to other clades in Selineae, contributing to a refined understanding of relationships. By analyzing a robust sample set, including ingroup and outgroup taxa, we employ high‐throughput sequencing technologies to capture a wide array of nuclear DNA sequences using the Angiosperms353 baits. Our bioinformatics pipeline, incorporating both HybPiper and HybPhaser workflows, facilitated the recovery and analysis of targeted sequences, ensuring high‐quality data for maximum likelihood and multispecies pseudo‐coalescent phylogenetic reconstructions. Our phylogenetic analyses do not recover a monophyletic PENA that includes all genera presumed to be part of this clade. Our results prompted the realignment of genera to include in the PENA clade. Genera that occur primarily in eastern North America are moved out of PENA. We also resolve, for the first time, the placement of the genus Eurytaenia within Apiaceae. This study contributes to a deeper understanding of the phylogenetic relationships within a taxonomically complex group of western North American Apiaceae, paving the way for broader insights into plant diversity and evolution in this botanically complex region.

Speciation processes in plants can be difficult to evaluate, but are essential to understanding evolutionary processes that lead to diversification. Determining the juncture at which a genetically and/or morphologically divergent population can be reliably considered a separate species is often challenging. This is particularly so with respect to recent divergences amongst closely related taxa wherein factors such as incomplete lineage sorting may yield confounding results. Taxa in the Cymopterus terebinthinus (Apiaceae) species complex have long puzzled botanists. Named entities in this group display similar, yet apparently distinct morphologies that have been classified as varieties under various generic names highlighting long‐standing nomenclatural instability. Previous phylogenetic studies have challenged the monophyly of this complex. This study aims to clarify taxonomic boundaries and infer evolutionary relationships among the four C. terebinthinus varieties and C. petraeus by applying phylogenetic inference and incorporating ecological, morphological, and geographical evidence. We sampled from populations of all varieties of C. terebinthinus and C. petraeus for target capture with the Angiosperms353 bait kit. We performed phylogenetic analyses with maximum likelihood (RAxML and IQ‐TREE) and coalescent‐based phylogenetic analysis (ASTRAL). We also conducted principal component analysis of soil samples and climatic variables. We find that C. terebinthinus and its varietal infrataxa comprise a monophyletic clade that includes C. petraeus. Clade groupings correspond to previous taxonomic assignments and morphology. Clades are often closely associated with geographical variables and at times correlated with ecological variables. Exceptions to this are here attributed to various evolutionary factors that often confound other phylogenetic analyses such as incomplete lineage sorting, introgression, and paralogous loci. Our findings suggests that geographical factors might play a major role in genetic and morphological differentiation in this complex. Despite finding well‐supported clades that correspond to defined morphological characters; further sampling among C. petraeus populations is required to make taxonomic decisions.

Pandanus ramromensis Callm., Y.W.Low & Buerki (Pandanaceae) from the summit of Khao Ram Rome (Nakhon Si Thammarat Province) in Peninsular Thailand is described here. The new species resembles Pandanus kedahensis H.St.John in its ecology and habit but differs by the dimensions of its leaves, leaf shape, syncarps and styles. The new species is provided with line drawings and field photographs, and is assigned a preliminary conservation status of Vulnerable (VU) using the IUCN Red List criteria.