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.

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.

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.