Phylotranscriptomics of Swertiinae (Gentianaceae) reveals that key floral traits are not phylogenetically correlated.

Establishing how lineages with similar traits are phylogenetically related remains critical for understanding the origin of biodiversity on Earth. Floral traits in plants are widely used to explore phylogenetic relationships and to delineate taxonomic groups. The subtribe Swertiinae (Gentianaceae) comprises more than 350 species with high floral diversity ranging from rotate to tubular corollas and possessing diverse nectaries. Here we performed phylogenetic analysis of 60 species from all 15 genera of the subtribe Swertiinae sensu Ho and Liu, representing the range of floral diversity, using data from the nuclear and plastid genomes. Extensive topological conflicts were present between the nuclear and plastome trees. Three of the 15 genera represented by multiple species are polyphyletic in both trees. Key floral traits including corolla type, absence or presence of lobe scales, nectary type, nectary position, and stigma type are randomly distributed in the nuclear and plastome trees without phylogenetic correlation. We also revealed the likely ancient hybrid origin of one large clade comprising 10 genera with diverse floral traits. These results highlight the complex evolutionary history of this subtribe. The phylogenies constructed here provide a basic framework for further exploring the ecological and genetic mechanisms underlying both species diversification and floral diversity.

Collections Education: The Extended Specimen and Data Acumen.

Biodiversity scientists must be fluent across disciplines; they must possess the quantitative, computational, and data skills necessary for working with large, complex data sets, and they must have foundational skills and content knowledge from ecology, evolution, taxonomy, and systematics. To effectively train the emerging workforce, we must teach science as we conduct science and embrace emerging concepts of data acumen alongside the knowledge, tools, and techniques foundational to organismal biology. We present an open education resource that updates the traditional plant collection exercise to incorporate best practices in twenty-first century collecting and to contextualize the activities that build data acumen. Students exposed to this resource gained skills and content knowledge in plant taxonomy and systematics, as well as a nuanced understanding of collections-based data resources. We discuss the importance of the extended specimen in fostering scientific discovery and reinforcing foundational concepts in biodiversity science, taxonomy, and systematics.

Plastomes resolve generic limits within tribe Clusieae (Clusiaceae) and reveal the new genus Arawakia.

Clusieae is an exclusively Neotropical tribe in the family Clusiaceae sensu stricto. Although tribes within Clusiaceae are morphologically and phylogenetically well-delimited, resolution among genera within these tribes remains elusive. The tribe Clusieae includes an estimated ∼500 species distributed among five genera: Chrysochlamys, Clusia, Dystovomita, Tovomita, and Tovomitopsis. In this study, we used nearly complete plastid genomes from 30 exemplar Clusieae species representing all genera recognized, plus two outgroups to infer the phylogeny of the tribe using Maximum Likelihood and Bayesian Inference. For comparison, we also inferred a phylogeny from the nuclear Internal Transcribed Spacer (ITS) region using the same methods. Our study corroborates earlier findings that Clusia is monophyletic while Tovomita is not. It also provides additional support to the hypothesis that Chrysochlamys and Tovomitopsis are not closely related despite gross morphological similarity. Tovomita is divided into three distantly related clades: (i) core Tovomita (including the type T. guianensis), (ii) T. croatii, and (iii) the T. weddelliana species complex. Members of the T. weddelliana complex are isolated from the core Tovomita, and placed in a well-supported clade that is sister to a clade composed of Chrysochlamys plus Clusia. Tovomita croatii is nested within Chrysochlamys. We propose taxonomic revisions to accommodate our phylogenetic findings, including the description of the new genus Arawakia, which includes the 18 species formerly recognized in the T. weddelliana species complex. Lectotypes are also designated for nine species (i.e., Arawakia angustata, A. lanceolata, A. lingulata, A. longicuneata, A. macrocarpa, A. oblanceolata, A. pithecobia, A. rhizophoroides, and A. weddelliana), and a taxonomic key for the identification of the six genera of Clusieae recognized is presented.

Plastid phylogenomic analysis of green plants: A billion years of evolutionary history.

PREMISE OF THE STUDY: For the past one billion years, green plants (Viridiplantae) have dominated global ecosystems, yet many key branches in their evolutionary history remain poorly resolved. Using the largest analysis of Viridiplantae based on plastid genome sequences to date, we examined the phylogeny and implications for morphological evolution at key nodes. METHODS: We analyzed amino acid sequences from protein-coding genes from complete (or nearly complete) plastomes for 1879 taxa, including representatives across all major clades of Viridiplantae. Much of the data used was derived from transcriptomes from the One Thousand Plants Project (1KP); other data were taken from GenBank. KEY RESULTS: Our results largely agree with previous plastid-based analyses. Noteworthy results include (1) the position of Zygnematophyceae as sister to land plants (Embryophyta), (2) a bryophyte clade (hornworts, mosses + liverworts), (3) Equisetum + Psilotaceae as sister to Marattiales + leptosporangiate ferns, (4) cycads + Ginkgo as sister to the remaining extant gymnosperms, within which Gnetophyta are placed within conifers as sister to non-Pinaceae (Gne-Cup hypothesis), and (5) Amborella, followed by water lilies (Nymphaeales), as successive sisters to all other extant angiosperms. Within angiosperms, there is support for Mesangiospermae, a clade that comprises magnoliids, Chloranthales, monocots, Ceratophyllum, and eudicots. The placements of Ceratophyllum and Dilleniaceae remain problematic. Within Pentapetalae, two major clades (superasterids and superrosids) are recovered. CONCLUSIONS: This plastid data set provides an important resource for elucidating morphological evolution, dating divergence times in Viridiplantae, comparisons with emerging nuclear phylogenies, and analyses of molecular evolutionary patterns and dynamics of the plastid genome.

Dispersal largely explains the Gondwanan distribution of the ancient tropical clusioid plant clade.

PREMISE OF THE STUDY: The clusioid clade (Malpighiales) has an ancient fossil record (∼90 Ma) and extant representatives exhibit a pantropical distribution represented on all former Gondwanan landmasses (Africa, Australia, India, Madagascar, and South America) except Antarctica. Several biogeographers have hypothesized that the clusioid distribution is an example of Gondwanan vicariance. Our aim is to test the hypothesis that the modern distribution of the clusioid clade is largely explained by Gondwanan fragmentation. METHODS: Using a four gene, 207-taxon data set we simultaneously estimated the phylogeny and divergence times of the clusioid clade using a Bayesian Markov chain Monte Carlo approach. Ancestral Area Reconstructions (AARs) were then conducted on a distribution of 1000 trees and summarized on a reduced phylogeny. KEY RESULTS: Divergence time estimates and AARs revealed only two or four cladogenic events that are potentially consistent with Gondwanan vicariance, depending on the placement of the ancient fossil Paleoclusia. In contrast, dispersal occurred on > 25% of the branches, indicating the current distribution of the clade likely reflects extensive recent dispersal during the Cenozoic (< 65 Ma), most of which occurred after the beginning of the Eocene (∼56 Ma). CONCLUSIONS: These results support growing evidence that suggests many traditionally recognized angiosperm clades (families and genera) are too young for their distributions to have been influenced strictly by Gondwanan fragmentation. Instead, it appears that corridors of dispersal may be the best explanation for numerous angiosperm clades with Gondwanan distributions.

Digitization workflows for flat sheets and packets of plants, algae, and fungi.

Effective workflows are essential components in the digitization of biodiversity specimen collections. To date, no comprehensive, community-vetted workflows have been published for digitizing flat sheets and packets of plants, algae, and fungi, even though latest estimates suggest that only 33% of herbarium specimens have been digitally transcribed, 54% of herbaria use a specimen database, and 24% are imaging specimens. In 2012, iDigBio, the U.S. National Science Foundation's (NSF) coordinating center and national resource for the digitization of public, nonfederal U.S. collections, launched several working groups to address this deficiency. Here, we report the development of 14 workflow modules with 7-36 tasks each. These workflows represent the combined work of approximately 35 curators, directors, and collections managers representing more than 30 herbaria, including 15 NSF-supported plant-related Thematic Collections Networks and collaboratives. The workflows are provided for download as Portable Document Format (PDF) and Microsoft Word files. Customization of these workflows for specific institutional implementation is encouraged.

Phylotranscriptomic analysis of the origin and early diversification of land plants.

Reconstructing the origin and evolution of land plants and their algal relatives is a fundamental problem in plant phylogenetics, and is essential for understanding how critical adaptations arose, including the embryo, vascular tissue, seeds, and flowers. Despite advances in molecular systematics, some hypotheses of relationships remain weakly resolved. Inferring deep phylogenies with bouts of rapid diversification can be problematic; however, genome-scale data should significantly increase the number of informative characters for analyses. Recent phylogenomic reconstructions focused on the major divergences of plants have resulted in promising but inconsistent results. One limitation is sparse taxon sampling, likely resulting from the difficulty and cost of data generation. To address this limitation, transcriptome data for 92 streptophyte taxa were generated and analyzed along with 11 published plant genome sequences. Phylogenetic reconstructions were conducted using up to 852 nuclear genes and 1,701,170 aligned sites. Sixty-nine analyses were performed to test the robustness of phylogenetic inferences to permutations of the data matrix or to phylogenetic method, including supermatrix, supertree, and coalescent-based approaches, maximum-likelihood and Bayesian methods, partitioned and unpartitioned analyses, and amino acid versus DNA alignments. Among other results, we find robust support for a sister-group relationship between land plants and one group of streptophyte green algae, the Zygnematophyceae. Strong and robust support for a clade comprising liverworts and mosses is inconsistent with a widely accepted view of early land plant evolution, and suggests that phylogenetic hypotheses used to understand the evolution of fundamental plant traits should be reevaluated.

From algae to angiosperms-inferring the phylogeny of green plants (Viridiplantae) from 360 plastid genomes.

BACKGROUND: Next-generation sequencing has provided a wealth of plastid genome sequence data from an increasingly diverse set of green plants (Viridiplantae). Although these data have helped resolve the phylogeny of numerous clades (e.g., green algae, angiosperms, and gymnosperms), their utility for inferring relationships across all green plants is uncertain. Viridiplantae originated 700-1500 million years ago and may comprise as many as 500,000 species. This clade represents a major source of photosynthetic carbon and contains an immense diversity of life forms, including some of the smallest and largest eukaryotes. Here we explore the limits and challenges of inferring a comprehensive green plant phylogeny from available complete or nearly complete plastid genome sequence data. RESULTS: We assembled protein-coding sequence data for 78 genes from 360 diverse green plant taxa with complete or nearly complete plastid genome sequences available from GenBank. Phylogenetic analyses of the plastid data recovered well-supported backbone relationships and strong support for relationships that were not observed in previous analyses of major subclades within Viridiplantae. However, there also is evidence of systematic error in some analyses. In several instances we obtained strongly supported but conflicting topologies from analyses of nucleotides versus amino acid characters, and the considerable variation in GC content among lineages and within single genomes affected the phylogenetic placement of several taxa. CONCLUSIONS: Analyses of the plastid sequence data recovered a strongly supported framework of relationships for green plants. This framework includes: i) the placement of Zygnematophyceace as sister to land plants (Embryophyta), ii) a clade of extant gymnosperms (Acrogymnospermae) with cycads + Ginkgo sister to remaining extant gymnosperms and with gnetophytes (Gnetophyta) sister to non-Pinaceae conifers (Gnecup trees), and iii) within the monilophyte clade (Monilophyta), Equisetales + Psilotales are sister to Marattiales + leptosporangiate ferns. Our analyses also highlight the challenges of using plastid genome sequences in deep-level phylogenomic analyses, and we provide suggestions for future analyses that will likely incorporate plastid genome sequence data for thousands of species. We particularly emphasize the importance of exploring the effects of different partitioning and character coding strategies.

Another look at the root of the angiosperms reveals a familiar tale.

Since the advent of molecular phylogenetics more than 25 years ago, a major goal of plant systematists has been to discern the root of the angiosperms. Although most studies indicate that Amborella trichopoda is sister to all remaining extant flowering plants, support for this position has varied with respect to both the sequence data sets and analyses employed. Recently, Goremykin et al. (2013) questioned the "Amborella-sister hypothesis" using a "noise-reduction" approach and reported a topology with Amborella + Nymphaeales (water lilies) sister to all remaining angiosperms. Through a series of analyses of both plastid genomes and mitochondrial genes, we continue to find mostly strong support for the Amborella-sister hypothesis and offer a rebuttal of Goremykin et al. (2013). The major tenet of Goremykin et al. is that the Amborella-sister position is determined by noisy data--that is, characters with high rates of change and lacking true phylogenetic signal. To investigate the signal in these noisy data further, we analyzed the discarded characters from their noise-reduced alignments. We recovered a tree identical to that of the currently accepted angiosperm framework, including the position of Amborella as sister to all other angiosperms, as well as all other major clades. Thus, the signal in the "noisy" data is consistent with that of our complete data sets--arguing against the use of their noise-reduction approach. We also determined that one of the alignments presented by Goremykin et al. yields results at odds with their central claim--their data set actually supports Amborella as sister to all other angiosperms, as do larger plastid data sets we present here that possess more complete taxon sampling both within the monocots and for angiosperms in general. Previous unpartitioned, multilocus analyses of mitochondrial DNA (mtDNA) data have provided the strongest support for Amborella + Nymphaeales as sister to other angiosperms. However, our analysis of third codon positions from mtDNA sequence data also supports the Amborella-sister hypothesis. Finally, we challenge the conclusion of Goremykin et al. that the first flowering plants were aquatic and herbaceous, reasserting that even if Amborella + water lilies, or water lilies alone, are sister to the rest of the angiosperms, the earliest angiosperms were not necessarily aquatic and/or herbaceous.

Data access for the 1,000 Plants (1KP) project.

The 1,000 plants (1KP) project is an international multi-disciplinary consortium that has generated transcriptome data from over 1,000 plant species, with exemplars for all of the major lineages across the Viridiplantae (green plants) clade. Here, we describe how to access the data used in a phylogenomics analysis of the first 85 species, and how to visualize our gene and species trees. Users can develop computational pipelines to analyse these data, in conjunction with data of their own that they can upload. Computationally estimated protein-protein interactions and biochemical pathways can be visualized at another site. Finally, we comment on our future plans and how they fit within this scalable system for the dissemination, visualization, and analysis of large multi-species data sets.

Phylogenomics and a posteriori data partitioning resolve the Cretaceous angiosperm radiation Malpighiales.

The angiosperm order Malpighiales includes ~16,000 species and constitutes up to 40% of the understory tree diversity in tropical rain forests. Despite remarkable progress in angiosperm systematics during the last 20 y, relationships within Malpighiales remain poorly resolved, possibly owing to its rapid rise during the mid-Cretaceous. Using phylogenomic approaches, including analyses of 82 plastid genes from 58 species, we identified 12 additional clades in Malpighiales and substantially increased resolution along the backbone. This greatly improved phylogeny revealed a dynamic history of shifts in net diversification rates across Malpighiales, with bursts of diversification noted in the Barbados cherries (Malpighiaceae), cocas (Erythroxylaceae), and passion flowers (Passifloraceae). We found that commonly used a priori approaches for partitioning concatenated data in maximum likelihood analyses, by gene or by codon position, performed poorly relative to the use of partitions identified a posteriori using a Bayesian mixture model. We also found better branch support in trees inferred from a taxon-rich, data-sparse matrix, which deeply sampled only the phylogenetically critical placeholders, than in trees inferred from a taxon-sparse matrix with little missing data. Although this matrix has more missing data, our a posteriori partitioning strategy reduced the possibility of producing multiple distinct but equally optimal topologies and increased phylogenetic decisiveness, compared with the strategy of partitioning by gene. These approaches are likely to help improve phylogenetic resolution in other poorly resolved major clades of angiosperms and to be more broadly useful in studies across the Tree of Life.

Phylogeny of the clusioid clade (Malpighiales): evidence from the plastid and mitochondrial genomes.

PREMISE OF THE STUDY: The clusioid clade includes five families (i.e., Bonnetiaceae, Calophyllaceae, Clusiaceae s.s., Hypericaceae, and Podostemaceae) represented by 94 genera and ≈1900 species. Species in this clade form a conspicuous element of tropical forests worldwide and are important in horticulture, timber production, and pharmacology. We conducted a taxon-rich multigene phylogenetic analysis of the clusioids to clarify phylogenetic relationships in this clade. METHODS: We analyzed plastid (matK, ndhF, and rbcL) and mitochondrial (matR) nucleotide sequence data using parsimony, maximum likelihood, and Bayesian inference. Our combined data set included 194 species representing all major clusioid subclades, plus numerous species spanning the taxonomic, morphological, and biogeographic breadth of the clusioid clade. KEY RESULTS: Our results indicate that Tovomita (Clusiaceae s.s.), Harungana and Hypericum (Hypericaceae), and Ledermanniella s.s. and Zeylanidium (Podostemaceae) are not monophyletic. In addition, we place four genera that have not been included in any previous molecular study: Ceratolacis, Diamantina, and Griffithella (Podostemaceae), and Santomasia (Hypericaceae). Finally, our results indicate that Lianthus, Santomasia, Thornea, and Triadenum can be safely merged into Hypericum (Hypericaceae). CONCLUSIONS: We present the first well-resolved, taxon-rich phylogeny of the clusioid clade. Taxon sampling and resolution within the clade are greatly improved compared to previous studies and provide a strong basis for improving the classification of the group. In addition, our phylogeny will form the foundation for our future work investigating the biogeography of tropical angiosperms that exhibit Gondwanan distributions.

Favorable climate change response explains non-native species' success in Thoreau's woods.

Invasive species have tremendous detrimental ecological and economic impacts. Climate change may exacerbate species invasions across communities if non-native species are better able to respond to climate changes than native species. Recent evidence indicates that species that respond to climate change by adjusting their phenology (i.e., the timing of seasonal activities, such as flowering) have historically increased in abundance. The extent to which non-native species success is similarly linked to a favorable climate change response, however, remains untested. We analyzed a dataset initiated by the conservationist Henry David Thoreau that documents the long-term phenological response of native and non-native plant species over the last 150 years from Concord, Massachusetts (USA). Our results demonstrate that non-native species, and invasive species in particular, have been far better able to respond to recent climate change by adjusting their flowering time. This demonstrates that climate change has likely played, and may continue to play, an important role in facilitating non-native species naturalization and invasion at the community level.