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The increasing frequency and severity of heatwaves will intensify stress on plants. Given regional variation in heatwave exposure and expected differences in thermal tolerance between species it is unlikely that all plant species will be affected equally by climate change. However, little is currently known about variation in the responses of plants to heat stress, or how those responses differ among closely related species adapted to different environments. Here we quantify the response of 17 Acacia species (175 RNA‐seq libraries), from across Australia's diverse biomes, to a multi‐day experimental heatwave treatment to identify variation in transcriptomic and physiological responses to heat stress. Genes with known heat response functions showed consistent responses across Acacia species. Up to 10% of all genes and over 100 gene families showed significant clinal variation in the magnitude of their expression plasticity across species. Specifically, gene families linked to the temperature stress response were overrepresented among significant relationships with home range temperature conditions. Gene expression responses seen on the first day of the heatwave were more frequently associated with home range climates, while expression responses by day four were more commonly related to photosystem II acclimation. Comparative transcriptomics on non‐model species has the potential to provide key information on stress response plasticity, especially when linked with our understanding of model species. Our study indicates that the pressing challenge to identifying potentially vulnerable species to climate change could be benefited by the further exploration of clinal variation in transcriptome plasticity. [ABSTRACT FROM AUTHOR]

Zieria buxijugum , Z. formosa , and Z. parrisiae are three closely related, Critically Endangered species of questionable taxonomic validity that occur within six kilometres of each other on the south coast of New South Wales, Australia. We investigated genetic relationships and diversity of these species, along with two related but taxonomically distinct congeners, Z. granulata and Z. tuberculata , and a possible undescribed taxon, Z. aff. tuberculata. Double-digest restriction-site associated sequencing (ddRADseq) was used to generate anonymous genomic loci that were used for phylogenetic, network, and genetic structure analyses, and for estimating genetic diversity of the threatened species. Our results support the current taxonomic status of Z. buxijugum , Z. formosa , and Z. parrisiae , and suggest that Z. aff. tuberculata warrants recognition as a distinct species. We detected no evidence of inbreeding in the three Critically Endangered species, and found their genetic diversity to be similar to that of the more widespread species Z. granulata and Z. tuberculata. Comparison of plant material held in ex situ collections at the Australian National Botanic Gardens with wild plants highlighted several genotypes of the Critically Endangered species that are not represented in the ex situ collection, and we provide suggestions for the future inclusion of those unrepresented genotypes. [ABSTRACT FROM AUTHOR]

Context: Giving up photosynthetic function is a bold evolutionary step for a plant, yet the evolutionary transition from autotrophy to mycoheterotrophy has occurred dozens of times. Comparing plastome sequences of mycoheterotrophs and autotrophs has identified recurring patterns of gene loss throughout a range of land plants, though more comparisons are required to see how broadly these patterns apply across the diversity of terrestrial plants. Mycoheterotrophy is especially common in Orchidaceae, with more than 40 transitions from autotrophy to mycoheterotrophy in the family. Aims: We sought to test generalised patterns of plastome degradation seen in other mycoheterotrophs by comparing two species in the genus Dipodium (Orchidaceae); one species is photosynthetic and the other appears to be a facultative mycoheterotroph species. Methods: We sequenced and assembled the plastomes of two Dipodium species and compared the two genomes to identify gene degradation or loss. Results: The two plastomes were nearly identical, with no degradation of photosynthesis genes in the putative mycoheterotroph, and both species have undergone loss or pseudogenisation of all plastid ndh (nicotinamide adenine dinucleotide + hydrogen specific dehydrogenase) genes. Conclusions: These results contrast with most other comparisons between photosynthetic and likely mycoheterotrophic relatives, where rapid degradation in mycoheterotroph plastome genes is common, and may suggest the leafless Dipodium species are capable of photosynthesis and may be in the early stages of transitioning to a fully heterotrophic lifestyle. Implications: Further investigation of trophic transitions in Dipodium , including sequencing more plastomes and measuring photosynthetic capability of the putative heterotrophs, will yield insights into the evolution of plant lineages that lose the ability to photosynthesise. Some plant species rely on fungal symbioses for energy, rather than the sun; such plants typically follow a general pattern of gene loss as they transition away from being photosynthetic. We found that an Australian orchid species typically regarded as being fully reliant on the fungal symbiont, retains the genes required for photosynthesis. This species may be able to utilise both energy sources, or may rather be only in the early stages of transitioning to fungal reliance. [ABSTRACT FROM AUTHOR]

The morphologically variable genus Archidendron is the second largest mimosoid legume genus from the Indomalayan-Australasian region, yet it has not been well represented in phylogenetic studies. Phylogenies that have included multiple representatives of Archidendron suggest it may not be monophyletic, and the same applies to Archidendropsis, another understudied genus of the Archidendron clade. The most comprehensive phylogeny of Archidendron and Archidendropsis to date is presented, based on four nuclear markers (ITS, ETS, SHMT and RBPCO). Exemplars from all genera of the wider Archidendron clade are sampled, including representatives of all series within Archidendron and the two subgenera of Archidendropsis. Our results confirm that Archidendron and Archidendropsis are not monophyletic. Within Archidendron, only one series (ser. Ptenopae) is resolved as monophyletic and species of Archidendron are divided into two primarily geographic lineages. One clade is distributed in western Malesia and mainland Asia and includes most representatives of series Clypeariae, while the other is mostly restricted to eastern Malesia and Australia and includes representatives of the seven other series plus two samples of series Clypeariae. No taxonomic changes are made for Archidendron due to the high level of topological uncertainty and the lack of discrete macromorphological characters separating these two lineages. Each of the two subgenera of Archidendropsis is monophyletic but they are not closely related. A new genus endemic to Queensland (Australia), Heliodendron Gill.K. Br. & Bayly, gen. nov., is described for the former Archidendropsis subg. Basaltica, and combinations for its three species are proposed: Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly, comb. nov., Heliodendron thozetianum (F. Muell.) Gill.K. Br. & Bayly, comb. nov., and Heliodendron xanthoxylon (C.T. White & W.D. Francis) Gill.K. Br. & Bayly, comb. nov. [ABSTRACT FROM AUTHOR]

Albrecht, D.E. & McLay, T.G.B. A new species of Brachyachne (Poaceae: Chloridoideae: Cynodonteae) from semi-arid Northern Territory and Western Australia, and additional notes on the genus. Nuytsia 33: 263-274. Brachyachne anisocarpa Albr. is described and illustrated, with notes on distribution, habitat and relationship with similar species. New distribution records of other Brachyachne (Benth.) Stapf species are provided, along with a key to Brachyachne species in Australia. The status of the genus is discussed based on an analysis of pre-existing and new molecular data. [ABSTRACT FROM AUTHOR]

Aim: To infer relationships between populations of the semi‐arid, mallee eucalypt, Eucalyptus behriana, to build hypotheses regarding evolution of major disjunctions in the species' distribution and to expand understanding of the biogeographical history of southeastern Australia. Location: Southeastern Australia. Taxon: Eucalyptus behriana (Myrtaceae, Angiospermae). Methods: We developed a large dataset of anonymous genomic loci for 97 samples from 11 populations of E. behriana using double digest restriction site‐associated DNA sequencing (ddRAD‐seq), to determine genetic relationships between the populations. These relationships, along with species distribution models, were used to construct hypotheses regarding environmental processes that have driven fragmentation of the species' distribution. Results: Greatest genetic divergence was between populations on either side of the Lower Murray Basin. Populations west of the Basin showed greater genetic divergence between one another than the eastern populations. The most genetically distinct population in the east (Long Forest) was separated from others by the Great Dividing Range. A close relationship was found between the outlying northernmost population (near West Wyalong) and those in the Victorian Goldfields despite a large disjunction between them. Conclusions: Patterns of genetic variation are consistent with a history of vicariant differentiation of disjunct populations. We infer that an early disjunction to develop in the species distribution was that across the Lower Murray Basin, an important biogeographical barrier separating many dry sclerophyll plant taxa in southeastern Australia. Additionally, our results suggest that the western populations fragmented earlier than the eastern ones. Fragmentation, both west and east of the Murray Basin, is likely tied to climatic changes associated with glacial‐interglacial cycles although it remains possible that major geological events including uplift of the Mount Lofty Ranges and basalt flows in the Newer Volcanics Province also played a role. [ABSTRACT FROM AUTHOR]

Eucalypts are a large and ecologically important group of plants on the Australian continent, and understanding their evolution is important in understanding evolution of the unique Australian flora. Previous phylogenies using plastome DNA, nuclear-ribosomal DNA, or random genome-wide SNPs, have been confounded by limited genetic sampling or by idiosyncratic biological features of the eucalypts, including widespread plastome introgression. Here we present phylogenetic analyses of Eucalyptus subgenus Eudesmia (22 species from western, northern, central and eastern Australia), in the first study to apply a target-capture sequencing approach using custom, eucalypt-specific baits (of 568 genes) to a lineage of Eucalyptus. Multiple accessions of all species were included, and target-capture data were supplemented by separate analyses of plastome genes (average of 63 genes per sample). Analyses revealed a complex evolutionary history likely shaped by incomplete lineage sorting and hybridization. Gene tree discordance generally increased with phylogenetic depth. Species, or groups of species, toward the tips of the tree are mostly supported, and three major clades are identified, but the branching order of these clades cannot be confirmed with confidence. Multiple approaches to filtering the nuclear dataset, by removing genes or samples, could not reduce gene tree conflict or resolve these relationships. Despite inherent complexities in eucalypt evolution, the custom bait kit devised for this research will be a powerful tool for investigating the evolutionary history of eucalypts more broadly., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2023. Published by Elsevier Inc. All rights reserved.)