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.

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.