Morphometrics and Phylogenomics of Coca (Erythroxylum spp.) Illuminate Its Reticulate Evolution, With Implications for Taxonomy.

South American coca (Erythroxylum coca and E. novogranatense) has been a keystone crop for many Andean and Amazonian communities for at least 8,000 years. However, over the last half-century, global demand for its alkaloid cocaine has driven intensive agriculture of this plant and placed it in the center of armed conflict and deforestation. To monitor the changing landscape of coca plantations, the United Nations Office on Drugs and Crime collects annual data on their areas of cultivation. However, attempts to delineate areas in which different varieties are grown have failed due to limitations around identification. In the absence of flowers, identification relies on leaf morphology, yet the extent to which this is reflected in taxonomy is uncertain. Here, we analyze the consistency of the current naming system of coca and its four closest wild relatives (the "coca clade"), using morphometrics, phylogenomics, molecular clocks, and population genomics. We include name-bearing type specimens of coca's closest wild relatives E. gracilipes and E. cataractarum. Morphometrics of 342 digitized herbarium specimens show that leaf shape and size fail to reliably discriminate between species and varieties. However, the statistical analyses illuminate that rounder and more obovate leaves of certain varieties could be associated with the subtle domestication syndrome of coca. Our phylogenomic data indicate extensive gene flow involving E. gracilipes which, combined with morphometrics, supports E. gracilipes being retained as a single species. Establishing a robust evolutionary-taxonomic framework for the coca clade will facilitate the development of cost-effective genotyping methods to support reliable identification.

The sexual lability hypothesis for the origin of the land plant generation cycle.

The evolution of the land plant alternation of generations has been an open question for the past 150 years. Two hypotheses have dominated the discussion: the antithetic hypothesis, which posits that the diploid sporophyte generation arose de novo and gradually increased in complexity, and the homologous hypothesis, which holds that land plant ancestors had independently living sporophytes and haploid gametophytes of similar complexity. Changes in ploidy levels were unknown to early researchers. The antithetic hypothesis is contradicted by generation cycles in Lower Devonian Rhynie chert plants, whose sporophytes and gametophytes have similar morphologies and by some Silurian sporophytes whose complexity exceeds that of Rhynie chert sporophytes. The oldest unambiguous bryophyte gametophytes (thalli) are from the upper Middle Devonian, with an unconnected sporophyte nearby. Based on the 2024 discovery that conjugate algae are paraphyletic to land plants, we present a new hypothesis for the evolution of the land plant generation cycle, focusing on labile ploidy levels and types of reproduction found in conjugate algae. Our 'sexual lability' hypothesis assumes a period of unstable generation cycles (as regards ploidy), likely with predominant clonal growth, as is common in conjugate algae, resulting in sporophytes and gametophytes of similar morphology. When sexual reproduction became stabilized, the timing of gamete fusion, meiosis, and resistant wall formation, which are heterochronic in some conjugate algae, became standardized, with wall formation permanently delayed. In our scenario, independently living adult sporophytes are the land plant ancestral condition, and life-long sporophyte retention on the gametophyte is a bryophyte apomorphy.

Hapsolutely: a user-friendly tool integrating haplotype phasing, network construction, and haploweb calculation.

Motivation: Haplotype networks are a routine approach to visualize relationships among alleles. Such visual analysis of single-locus data is still of importance, especially in species diagnosis and delimitation, where a limited amount of sequence data usually are available and sufficient, along with other datasets in the framework of integrative taxonomy. In diploid organisms, this often requires separating (phasing) sequences with heterozygotic positions, and typically separate programs are required for phasing, reformatting of input files, and haplotype network construction. We therefore developed Hapsolutely, a user-friendly program with an ergonomic graphical user interface that integrates haplotype phasing from single-locus sequences with five approaches for network/genealogy reconstruction. Results: Among the novel options implemented, Hapsolutely integrates phasing and graphical reconstruction steps of haplotype networks, supports input of species partition data in the common SPART and SPART-XML formats, and calculates and visualizes haplowebs and fields for recombination, thus allowing graphical comparison of allele distribution and allele sharing among subsets for the purpose of species delimitation. The new tool has been specifically developed with a focus on the workflow in alpha-taxonomy, where exploring fields for recombination across alternative species partitions may help species delimitation. Availability and implementation: Hapsolutely is written in Python, and integrates code from Phase, SeqPHASE, and PopART in C++ and Haxe. Compiled stand-alone executables for MS Windows and Mac OS along with a detailed manual can be downloaded from https://www.itaxotools.org; the source code is openly available on GitHub (https://github.com/iTaxoTools/Hapsolutely).

Efficient purging of deleterious mutations contributes to the survival of a rare conifer.

Cupressaceae is a conifer family rich in plants of horticultural importance, including Cupressus, Chamaecyparis, Juniperus, and Thuja, yet genomic surveys are lacking for this family. Cupressus gigantea, one of the many rare conifers that are threatened by climate change and anthropogenic habitat fragmentation, plays an ever-increasing role in ecotourism in Tibet. To infer how past climate change has shaped the population evolution of this species, we generated a de novo chromosome-scale genome (10.92 Gb) and compared the species' population history and genetic load with that of a widespread close relative, C. duclouxiana. Our demographic analyses, based on 83 re-sequenced individuals from multiple populations of the two species, revealed a sharp decline of population sizes during the first part of the Quaternary. However, populations of C. duclouxiana then started to recover, while C. gigantea populations continued to decrease until recently. The total genomic diversity of C. gigantea is smaller than that of C. duclouxiana, but contrary to expectations, C. gigantea has fewer highly and mildly deleterious mutations than C. duclouxiana, and simulations and statistical tests support purifying selection during prolonged inbreeding as the explanation. Our results highlight the evolutionary consequences of decreased population size on the genetic burden of a long-lived endangered conifer with large genome size and suggest that genetic purging deserves more attention in conservation management.

Subgenome-aware analyses reveal the genomic consequences of ancient allopolyploid hybridizations throughout the cotton family.

Malvaceae comprise some 4,225 species in 243 genera and nine subfamilies and include economically important species, such as cacao, cotton, durian, and jute, with cotton an important model system for studying the domestication of polyploids. Here, we use chromosome-level genome assemblies from representatives of five or six subfamilies (depending on the placement of Ochroma) to differentiate coexisting subgenomes and their evolution during the family's deep history. The results reveal that the allohexaploid Helicteroideae partially derive from an allotetraploid Sterculioideae and also form a component of the allodecaploid Bombacoideae and Malvoideae. The ancestral Malvaceae karyotype consists of 11 protochromosomes. Four subfamilies share a unique reciprocal chromosome translocation, and two other subfamilies share a chromosome fusion. DNA alignments of single-copy nuclear genes do not yield the same relationships as inferred from chromosome structural traits, probably because of genes originating from different ancestral subgenomes. These results illustrate how chromosome-structural data can unravel the evolutionary history of groups with ancient hybrid genomes.

Mutualisms drive plant trait evolution beyond interaction-related traits.

Mutualisms have driven the evolution of extraordinary structures and behavioural traits, but their impact on traits beyond those directly involved in the interaction remains unclear. We addressed this gap using a highly evolutionarily replicated system - epiphytes in the Rubiaceae forming symbioses with ants. We employed models that allow us to test the influence of discrete mutualistic traits on continuous non-mutualistic traits. Our findings are consistent with mutualism shaping the pace of morphological evolution, strength of selection and long-term mean of non-mutualistic traits in function of mutualistic dependency. While specialised and obligate mutualisms are associated with slower trait change, less intimate, facultative and generalist mutualistic interactions - which are the most common - have a greater impact on non-mutualistic trait evolution. These results challenge the prevailing notion that mutualisms solely affect the evolution of interaction-related traits via stabilizing selection and instead demonstrate a broader role for mutualisms in shaping trait evolution.

The origin and speciation of orchids.

Orchids constitute one of the most spectacular radiations of flowering plants. However, their origin, spread across the globe, and hotspots of speciation remain uncertain due to the lack of an up-to-date phylogeographic analysis. We present a new Orchidaceae phylogeny based on combined high-throughput and Sanger sequencing data, covering all five subfamilies, 17/22 tribes, 40/49 subtribes, 285/736 genera, and c. 7% (1921) of the 29 524 accepted species, and use it to infer geographic range evolution, diversity, and speciation patterns by adding curated geographical distributions from the World Checklist of Vascular Plants. The orchids' most recent common ancestor is inferred to have lived in Late Cretaceous Laurasia. The modern range of Apostasioideae, which comprises two genera with 16 species from India to northern Australia, is interpreted as relictual, similar to that of numerous other groups that went extinct at higher latitudes following the global climate cooling during the Oligocene. Despite their ancient origin, modern orchid species diversity mainly originated over the last 5 Ma, with the highest speciation rates in Panama and Costa Rica. These results alter our understanding of the geographic origin of orchids, previously proposed as Australian, and pinpoint Central America as a region of recent, explosive speciation.

Integrated global assessment of the natural forest carbon potential.

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2-5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151-363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.

DNA sequences from type specimens and type strains - how to increase their number and improve their annotation in NCBI GenBank and related databases.

Scientific names permit humans and search engines to access knowledge about the biodiversity that surrounds us, and names linked to DNA sequences are playing an ever-greater role in search-and-match identification procedures. Here, we analyze how users and curators of the National Center for Biotechnology Information (NCBI) are flagging and curating sequences derived from nomenclatural type material, which is the only way to improve the quality of DNA-based identification in the long run. For prokaryotes, 18,281 genome assemblies from type strains have been curated by NCBI staff and improve the quality of prokaryote naming. For Fungi, type-derived sequences representing over 21,000 species are now essential for fungus naming and identification. For the remaining eukaryotes, however, the numbers of sequences identifiable as type-derived are minuscule, representing only 1,000 species of arthropods, 8,441 vertebrates, and 430 embryophytes. An increase in the production and curation of such sequences will come from (i) sequencing of types or topotypic specimens in museum collections, (ii) the March 2023 rule changes at the International Nucleotide Sequence Database Collaboration requiring more metadata for specimens, and (iii) efforts by data submitters to facilitate curation, including informing NCBI curators about a specimen's type status. We illustrate different type-data submission journeys and provide best-practice examples from a range of organisms. Expanding the number of type-derived sequences in DNA databases, especially of eukaryotes, is crucial for capturing, documenting, and protecting biodiversity.

The global biogeography of tree leaf form and habit.

Understanding what controls global leaf type variation in trees is crucial for comprehending their role in terrestrial ecosystems, including carbon, water and nutrient dynamics. Yet our understanding of the factors influencing forest leaf types remains incomplete, leaving us uncertain about the global proportions of needle-leaved, broadleaved, evergreen and deciduous trees. To address these gaps, we conducted a global, ground-sourced assessment of forest leaf-type variation by integrating forest inventory data with comprehensive leaf form (broadleaf vs needle-leaf) and habit (evergreen vs deciduous) records. We found that global variation in leaf habit is primarily driven by isothermality and soil characteristics, while leaf form is predominantly driven by temperature. Given these relationships, we estimate that 38% of global tree individuals are needle-leaved evergreen, 29% are broadleaved evergreen, 27% are broadleaved deciduous and 5% are needle-leaved deciduous. The aboveground biomass distribution among these tree types is approximately 21% (126.4 Gt), 54% (335.7 Gt), 22% (136.2 Gt) and 3% (18.7 Gt), respectively. We further project that, depending on future emissions pathways, 17-34% of forested areas will experience climate conditions by the end of the century that currently support a different forest type, highlighting the intensification of climatic stress on existing forests. By quantifying the distribution of tree leaf types and their corresponding biomass, and identifying regions where climate change will exert greatest pressure on current leaf types, our results can help improve predictions of future terrestrial ecosystem functioning and carbon cycling.

Effect of climate warming on the timing of autumn leaf senescence reverses after the summer solstice.

Climate change is shifting the growing seasons of plants, affecting species performance and biogeochemical cycles. Yet how the timing of autumn leaf senescence in Northern Hemisphere forests will change remains uncertain. Using satellite, ground, carbon flux, and experimental data, we show that early-season and late-season warming have opposite effects on leaf senescence, with a reversal occurring after the year's longest day (the summer solstice). Across 84% of the northern forest area, increased temperature and vegetation activity before the solstice led to an earlier senescence onset of, on average, 1.9 ± 0.1 days per °C, whereas warmer post-solstice temperatures extended senescence duration by 2.6 ± 0.1 days per °C. The current trajectories toward an earlier onset and slowed progression of senescence affect Northern Hemisphere-wide trends in growing-season length and forest productivity.

No plant is an island.

Most of the world's ecosystems are dominated by plants, and preserving the natural and agricultural landscapes that we depend on therefore requires understanding plants and their interactions at local and global scales. This is challenging because plants' ways of perceiving each other and communicating with each other and with animals are so fundamentally different from the ways we animals communicate with, and manipulate, each other. The collection of articles in the present issue of Current Biology illustrates the progress being made in deciphering some of the processes and mechanisms involved in plant interactions at different scales. While the topic of interactions with plants is very broad, any overview will require covering chemical signals and their reception; mutualisms and symbioses; interactions with pathogens; and interactions in communities. Approaches taken in these fields range from molecular biology and physiology to ecology.

"My Reputation is at Stake." Humboldt's Mountain Plant Geography in the Making (1803-1825).

Alexander von Humboldt's depictions of mountain vegetation are among the most iconic nineteenth century illustrations in the biological sciences. Here we analyse the contemporary context and empirical data for all these depictions, namely the Tableau physique des Andes (1803, 1807), the Geographiae plantarum lineamenta (1815), the Tableau physique des Îles Canaries (1817), and the Esquisse de la Géographie des plantes dans les Andes de Quito (1824/1825). We show that the Tableau physique des Andes does not reflect Humboldt and Bonpland's field data and presents a flawed depiction of plant occurrences and vertical succession of vegetation belts, arising from Humboldt's misreading of La Condamine's description (1751). Humboldt's 1815 depiction, by contrast, shows a distribution of high-vegetation belts that is consistent with La Condamine's description, while the 1824 depiction drops innovations made in 1815 and returns to simply showing numerous species' names, thus not applying Humboldt's own earlier zonation framework. Our analysis of contemporary reactions to Humboldt's TPA includes Francis Hall's posthumously published 1834 illustration of Andean plant zonation near Quito and Humboldt's reaction to Hall's critique. Throughout his work on plant geography, Humboldt disregarded some of his own observations, or confused them. At stake was his reputation as an innovator in the field of plant geography and a discoverer of the sequence of high-elevation vegetation belts on the world's mountains.

Genome structure-based Juglandaceae phylogenies contradict alignment-based phylogenies and substitution rates vary with DNA repair genes.

In lineages of allopolyploid origin, sets of homoeologous chromosomes may coexist that differ in gene content and syntenic structure. Presence or absence of genes and microsynteny along chromosomal blocks can serve to differentiate subgenomes and to infer phylogenies. We here apply genome-structural data to infer relationships in an ancient allopolyploid lineage, the walnut family (Juglandaceae), by using seven chromosome-level genomes, two of them newly assembled. Microsynteny and gene-content analyses yield identical topologies that place Platycarya with Engelhardia as did a 1980s morphological-cladistic study. DNA-alignment-based topologies here and in numerous earlier studies instead group Platycarya with Carya and Juglans, perhaps misled by past hybridization. All available data support a hybrid origin of Juglandaceae from extinct or unsampled progenitors nested within, or sister to, Myricaceae. Rhoiptelea chiliantha, sister to all other Juglandaceae, contains proportionally more DNA repair genes and appears to evolve at a rate 2.6- to 3.5-times slower than the remaining species.