Target sequence data shed new light on the infrafamilial classification of Araceae.

PREMISE: Recent phylogenetic studies of the Araceae have confirmed the position of the duckweeds nested within the aroids, and the monophyly of a clade containing all the unisexual flowered aroids plus the bisexual-flowered Calla palustris. The main objective of the present study was to better resolve the deep phylogenetic relationships among the main lineages within the family, particularly the relationships between the eight currently recognized subfamilies. We also aimed to confirm the phylogenetic position of the enigmatic genus Calla in relation to the long-debated evolutionary transition between bisexual and unisexual flowers in the family. METHODS: Nuclear DNA sequence data were generated for 128 species across 111 genera (78%) of Araceae using target sequence capture and the Angiosperms 353 universal probe set. RESULTS: The phylogenomic data confirmed the monophyly of the eight Araceae subfamilies, but the phylogenetic position of subfamily Lasioideae remains uncertain. The genus Calla is included in subfamily Aroideae, which has also been expanded to include Zamioculcadoideae. The tribe Aglaonemateae is newly defined to include the genera Aglaonema and Boycea. CONCLUSIONS: Our results strongly suggest that new research on African genera (Callopsis, Nephthytis, and Anubias) and Calla will be important for understanding the early evolution of the Aroideae. Also of particular interest are the phylogenetic positions of the isolated genera Montrichardia, Zantedeschia, and Anchomanes, which remain only moderately supported here.

A nuclear target sequence capture probe set for phylogeny reconstruction of the charismatic plant family Bignoniaceae.

The plant family Bignoniaceae is a conspicuous and charismatic element of the tropical flora. The family has a complex taxonomic history, with substantial changes in the classification of the group during the past two centuries. Recent re-classifications at the tribal and generic levels have been largely possible by the availability of molecular phylogenies reconstructed using Sanger sequencing data. However, our complete understanding of the systematics, evolution, and biogeography of the family remains incomplete, especially due to the low resolution and support of different portions of the Bignoniaceae phylogeny. To overcome these limitations and increase the amount of molecular data available for phylogeny reconstruction within this plant family, we developed a bait kit targeting 762 nuclear genes, including 329 genes selected specifically for the Bignoniaceae; 348 genes obtained from the Angiosperms353 with baits designed specifically for the family; and, 85 low-copy genes of known function. On average, 77.4% of the reads mapped to the targets, and 755 genes were obtained per species. After removing genes with putative paralogs, 677 loci were used for phylogenetic analyses. On-target genes were compared and combined in the Exon-Only dataset, and on-target + off-target regions were combined in the Supercontig dataset. We tested the performance of the bait kit at different taxonomic levels, from family to species-level, using 38 specimens of 36 different species of Bignoniaceae, representing: 1) six (out of eight) tribal level-clades (e.g., Bignonieae, Oroxyleae, Tabebuia Alliance, Paleotropical Clade, Tecomeae, and Jacarandeae), only Tourrettieae and Catalpeae were not sampled; 2) all 20 genera of Bignonieae; 3) seven (out of nine) species of Dolichandra (e.g., D. chodatii, D. cynanchoides, D. dentata, D. hispida, D. quadrivalvis, D. uncata, and D. uniguis-cati), only D. steyermarkii and D. unguiculata were not sampled; and 4) three individuals of Dolichandra unguis-cati. Our data reconstructed a well-supported phylogeny of the Bignoniaceae at different taxonomic scales, opening new perspectives for a comprehensive phylogenetic framework for the family as a whole.

Complete Chloroplast Genomes of Anthurium huixtlense and Pothos scandens (Pothoideae, Araceae): Unique Inverted Repeat Expansion and Contraction Affect Rate of Evolution.

The subfamily Pothoideae belongs to the ecologically important plant family Araceae. Here, we report the chloroplast genomes of two species of the subfamily Pothoideae: Anthurium huixtlense (size: 163,116 bp) and Pothos scandens (size: 164,719 bp). The chloroplast genome of P. scandens showed unique contraction and expansion of inverted repeats (IRs), thereby increasing the size of the large single-copy region (LSC: 102,956 bp) and decreasing the size of the small single-copy region (SSC: 6779 bp). This led to duplication of many single-copy genes due to transfer to IR regions from the small single-copy (SSC) region, whereas some duplicate genes became single copy due to transfer to large single-copy regions. The rate of evolution of protein-coding genes was affected by the contraction and expansion of IRs; we found higher mutation rates for genes that exist in single-copy regions as compared to those in IRs. We found a 2.3-fold increase of oligonucleotide repeats in P. scandens when compared with A. huixtlense, whereas amino acid frequency and codon usage revealed similarities. The ratio of transition to transversion mutations was 2.26 in P. scandens and 2.12 in A. huixtlense. Transversion mutations mostly translated in non-synonymous substitutions. The phylogenetic inference of the limited species showed the monophyly of the Araceae subfamilies. Our study provides insight into the molecular evolution of chloroplast genomes in the subfamily Pothoideae and family Araceae.

Molecular evolution of chloroplast genomes in Monsteroideae (Araceae).

MAIN CONCLUSION: This study provides broad insight into the chloroplast genomes of the subfamily Monsteroideae. The identified polymorphic regions may be suitable for designing unique and robust molecular markers for phylogenetic inference. Monsteroideae is the third largest subfamily (comprises 369 species) and one of the early diverging lineages of the monocot plant family Araceae. The phylogeny of this important subfamily is not well resolved at the species level due to scarcity of genomic resources and suitable molecular markers. Here, we report annotated chloroplast genome sequences of four Monsteroideae species: Spathiphyllum patulinervum, Stenospermation multiovulatum, Monstera adansonii, and Rhaphidophora amplissima. The quadripartite chloroplast genomes (size range 163,335-164,751 bp) consist of a pair of inverted repeats (25,270-25,931 bp), separating a small single copy region (21,448-22,346 bp) from a large single copy region (89,714-91,841 bp). The genomes contain 114 unique genes, including four rRNA genes, 80 protein-coding genes, and 30 tRNA genes. Gene features, amino acid frequencies, codon usage, GC contents, oligonucleotide repeats, and inverted repeats dynamics exhibit similarities among the four genomes. Higher rate of synonymous substitutions was observed as compared to non-synonymous substitutions in 76 protein-coding genes. Positive selection was observed in seven protein-coding genes, including psbK, ndhK, ndhD, rbcL, accD, rps8, and ycf2. Our included species of Araceae showed the monophyly in Monsteroideae and other subfamilies. We report 30 suitable polymorphic regions. The polymorphic regions identified here might be suitable for designing unique and robust markers for inferring the phylogeny and phylogeography among closely related species within the genus Spathiphyllum and among distantly related species within the subfamily Monsteroideae. The chloroplast genomes presented here are a valuable contribution towards understanding the molecular evolutionary dynamics in the family Araceae.

Utility of targeted sequence capture for phylogenomics in rapid, recent angiosperm radiations: Neotropical Burmeistera bellflowers as a case study.

Targeted sequence capture is a promising approach for large-scale phylogenomics. However, rapid evolutionary radiations pose significant challenges for phylogenetic inference (e.g. incomplete lineages sorting (ILS), phylogenetic noise), and the ability of targeted nuclear loci to resolve species trees despite such issues remains poorly studied. We test the utility of targeted sequence capture for inferring phylogenetic relationships in rapid, recent angiosperm radiations, focusing on Burmeistera bellflowers (Campanulaceae), which diversified into ~130 species over less than 3 million years. We compared phylogenies estimated from supercontig (exons plus flanking sequences), exon-only, and flanking-only datasets with 506-546 loci (~4.7 million bases) for 46 Burmeistera species/lineages and 10 outgroup taxa. Nuclear loci resolved backbone nodes and many congruent internal relationships with high support in concatenation and coalescent-based species tree analyses, and inferences were largely robust to effects of missing taxa and base composition biases. Nevertheless, species trees were incongruent between datasets, and gene trees exhibited remarkably high levels of conflict (~4-60% congruence, ~40-99% conflict) not simply driven by poor gene tree resolution. Higher gene tree heterogeneity at shorter branches suggests an important role of ILS, as expected for rapid radiations. Phylogenetic informativeness analyses also suggest this incongruence has resulted from low resolving power at short internal branches, consistent with ILS, and homoplasy at deeper nodes, with exons exhibiting much greater risk of incorrect topologies due to homoplasy than other datasets. Our findings suggest that targeted sequence capture is feasible for resolving rapid, recent angiosperm radiations, and that results based on supercontig alignments containing nuclear exons and flanking sequences have higher phylogenetic utility and accuracy than either alone. We use our results to make practical recommendations for future target capture-based studies of Burmeistera and other rapid angiosperm radiations, including that such studies should analyze supercontigs to maximize the phylogenetic information content of loci.

Evolutionary dynamics of chloroplast genomes in subfamily Aroideae (Araceae).

Aroideae is the largest and most diverse subfamily of the plant family Araceae. Despite its agricultural and horticultural importance, the genomic resources are sparse for this subfamily. Here, we report de novo assembled and fully annotated chloroplast genomes of 13 Aroideae species. The quadripartite chloroplast genomes (size range of 158,177-170,037 bp) are comprised of a large single copy (LSC; 75,594-94,702 bp), a small single copy (SSC; 12,903-23,981 bp) and a pair of inverted repeats (IRs; 25,266-34,840 bp). Notable gene rearrangements and IRs contraction / expansions were found for Anchomanes hookeri and Zantedeschia aethiopica. Codon usage, amino acid frequencies, oligonucleotide repeats, GC contents, and gene features revealed similarities among the 13 species. The number of oligonucleotide repeats was uncorrelated with genome size or phylogenetic position of the species. Phylogenetic analyses corroborated the monophyly of Aroideae but were unable to resolve the positions of Calla and Schismatoglottis.

Resolving the rapid plant radiation of early diverging lineages in the tropical Zingiberales: Pushing the limits of genomic data.

Many cases of rapid evolutionary radiations in plant and animal lineages are known; however phylogenetic relationships among these lineages have been difficult to resolve by systematists. Increasing amounts of genomic data have been sequentially applied in an attempt to resolve these radiations, dissecting their evolutionary patterns into a series of bifurcating events. Here we explore one such rapid radiation in the tropical plant order Zingiberales (the bananas and relatives) which includes eight families, approximately 110 genera, and more than 2600 species. One clade, the "Ginger families", including (Costaceae + Zingiberaceae) (Marantaceae + Cannaceae), has been well-resolved and well-supported in all previous studies. However, well-supported reconstructions among the "Banana families" (Musaceae, Heliconiaceae, Lowiaceae, Strelitziaceae), which most likely diverged about 90 Mya, have been difficult to confirm. Supported with anatomical, morphological, single locus, and genome-wide data, nearly every possible phylogenetic placement has been proposed for these families. In an attempt to resolve this complex evolutionary event, hybridization-based target enrichment was used to obtain sequences from up to 378 putatively orthologous low-copy nuclear genes (all ≥ 960 bp). Individual gene trees recovered multiple topologies among the early divergent lineages, with varying levels of support for these relationships. One topology of the "Banana families" (Musaceae (Heliconiaceae (Lowiaceae + Strelitziaceae))), which has not been suggested until now, was almost consistently recovered in all multilocus analyses of the nuclear dataset (concatenated - ExaML, coalescent - ASTRAL and ASTRID, supertree - MRL, and Bayesian concordance - BUCKy). Nevertheless, the multiple topologies recovered among these lineages suggest that even large amounts of genomic data might not be able to fully resolve relationships at this phylogenetic depth. This lack of well-supported resolution could suggest methodological problems (i.e., violation of model assumptions in both concatenated and coalescent analyses) or more likely reflect an evolutionary history shaped by an explosive, rapid, and nearly simultaneous polychotomous radiation in this group of plants towards the end of the Cretaceous, perhaps driven by vertebrate pollinator selection.

Phylogenetic relationships of Burmeistera (Campanulaceae: Lobelioideae): Combining whole plastome with targeted loci data in a recent radiation.

The field of molecular systematics has benefited greatly with the advent of high-throughput sequencing (HTS), making large genomic datasets commonplace. However, a large number of targeted Sanger sequences produced by many studies over the last two decades are publicly available and should not be overlooked. In this study, we elucidate the phylogenetic relationships of the plant genus Burmeistera (Campanulaceae: Lobelioideae), while investigating how to best combine targeted Sanger loci with HTS data. We sequence, annotate, and analyze complete to nearly complete plastomes for a subset of the genus. We then combine these data with a much larger taxonomic dataset for which only Sanger sequences are available, making this the most comprehensively sampled study in the genus to date. We show that using a phylogeny inferred from the species with plastome data as a topological constraint for the larger dataset increases the resolution of our data and produces a more robust evolutionary hypothesis for the group. We then use the resulting phylogeny to study the evolution of morphological traits thought to be important in Burmeistera, and assess their usefulness in the current taxonomic classification of the genus. The main morphological character used to delimit subgeneric sections, the presence or absence of hairs on the apex of the two ventral anthers, shows a complex evolutionary history with many changes in the tree, suggesting that this character should not be used for taxonomic classification. Although it is too soon to propose a new subgeneric classification for Burmeistera, our results highlight some morphological traits shared by whole clades that could potentially be used in future taxonomic work.

A reassessment of Anthurium species with palmately divided leaves, and a reinterpretation of Anthurium section Dactylophyllium (Araceae).

A reappraisal is made of the Anthurium Schott species with palmately divided leaves with 3 or more segments free to the base (i.e. palmatisect leaves), previously recognized as section Dactylophyllium Schott (Engler), as well as those species with 5 or more segments united at the base (i.e. palmatifid leaves), formerly placed in section Schizoplacium Schott (Engler). New molecular data indicates that several species (Anthurium pedatum (Kunth) Schott, Anthurium pedatoradiatum Schott, and possibly, Anthurium podophyllum (Schltdl. & Cham.) Kunth) should be excluded from section Schizoplacium, and other species previously placed in that section cannot be separated from section Dactylophyllium. Thus, Anthurium section Schizoplacium is here synonymized within section Dactylophyllium and type species are designated for both groups. This paper also provides an updated description of section Dactylophyllium as here emended, listing the 24 accepted taxa now included (20 species and 4 varieties or subspecies), along with their geographic distributions.