International Journal of Plant Sciences

Journal Information
ISSN / EISSN : 0006-8071 / 1537-5315
Published by: University of Chicago Press (10.1086)
Total articles ≅ 16,412
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, Ruth A. Stockey, Garland R. Upchurch, Mary L. Berbee
International Journal of Plant Sciences, Volume 182, pp 712-729; https://doi.org/10.1086/715635

Abstract:
Premise of research. Mesozoic to Cenozoic fungi forming scutella, shield-like coverings of sporulating tissue on leaf surfaces, offer insights into the diversification of filamentous ascomycetes. We found a new fungal sporocarp type consisting of radiate scutella growing from the stomata of leaves of a conifer in a survey of dispersed plant cuticles from the Lower Cretaceous of Virginia. Here, we interpret the new morphotype and compare it with other fossil groups and with extant taxa.Methodology. We isolated fragments of conifer cuticles colonized by the fungus from macerated clays of the Potomac Group, lower Zone 1 (Aptian, 125–113 Ma), and studied them using light microscopy. We analyzed the anatomy of scutella of living taxa and compared the fossils with extant taxa producing either rhizothyria, asexual sporocarps that release spores from below the outer edge of the scutellum, or thyriothecia, sporocarps that release spores through dorsal cracks or an ostiole.Pivotal results. Stomatothyrium placocentrum gen. et sp. nov. has a radial arrangement of scutellum hyphae, characteristic of extant and fossil thyriothecial species in Dothideomycetes (Ascomycota). The scutella develop cracks on the dorsal surface that may show the dehiscence mechanism. Unusually for dehiscence in Dothideomycetes, the cracks follow the scutellum circumference rather than its radius. Each scutellum arises from a host plant stoma, appearing first as a hyphal columella that broadens into a flat scutellum disk on the leaf surface. The morphotype is common, and we found more than 63 specimens at different developmental stages on cuticle fragments.Conclusions. Its unique morphology suggests that S. placocentrum gen. et sp. nov. represents a now extinct group of leaf-dwelling Dothideomycetes that formed thyriothecia. This discovery contributes to our understanding of the range of character combinations of early epiphyllous Ascomycota.
, Alfredo Ortega-Rubio, Neftalí Gutiérrez-Rivera, Pedro P. Garcillán
International Journal of Plant Sciences, Volume 182, pp 695-711; https://doi.org/10.1086/715637

Abstract:
Premise of research. Brahea edulis is an endangered palm endemic to the oceanic island of Guadalupe, Mexico, with a small population of just about 4000 individuals; it was chronically grazed by goats for about two centuries. The evolutionary specificities of insular biotas provide unique scenarios for studying the roles of geography, demography, and climate in driving population divergence. A comprehensive comparison between insular and mainland sister species contributes to a much better understanding of the species-specific responses to the ecological drivers of diversity, divergence, and speciation.Methodology. Here we used a comparative approach coupled with genomic (genotyping by sequencing; single-nucleotide polymorphisms) data to analyze samples from island and mainland Brahea palm species and elucidate their diversity, population divergence, and demographic history.Pivotal results. Genetic diversity analyses revealed higher diversity in insular palms compared with their mainland sister species. Genetic relationships among palm individuals on Guadalupe Island resulted in two strongly diverged clusters that reflected their geographic distributions. Divergence among B. edulis populations was mostly driven by the joint effect of low migration and the climatic heterogeneity of the island’s conditions. Using approximate Bayesian analysis, we further evaluated the demographic history of B. edulis. We found the genetic signatures of demographic fluctuations, inferring an effective population size (Ne) reduction that occurred in the late Quaternary and relatively low current Ne.Conclusions. These findings contribute to the ever-growing body of evidence that low genetic diversity in island populations cannot always be generalized. Besides, genetic diversity and differentiation on islands are more likely to be species specific and are strongly influenced by population size and historical factors such as the time since the population was established, ecological characteristics of the island, and anthropogenic impact. Our results also represent groundwork for future conservation and restoration programs for this endangered insular palm species.
Linda Zhang,
International Journal of Plant Sciences, Volume 182, pp 663-681; https://doi.org/10.1086/715638

Abstract:
Premise of research. Fused or connate leaves are a well-known phenomenon observed across a limited number of angiosperm clades, and no study has attempted to examine this form of fusion from an evolutionary, morphometric, or functional perspective. We examined leaf fusion in honeysuckles, specifically the Periclymenum clade (∼22 species) of Lonicera (Caprifoliaceae, Dipsacales), which exhibits variation in leaf shape, degree of fusion, and the position of fused leaves. As fused leaves co-occurred with reproductive structures, evolutionary correlations between leaf fusion and inflorescence architecture were also examined.Methodology. Variation of leaf fusion was assessed using elliptical Fourier analysis, and multiple individuals of 19 of the 22 species of Periclymenum were sampled. As fused leaves occurred only on reproductive shoots, a suite of inflorescence characters were also studied. A phylogeny for Periclymenum was reconstructed using published sequence data, and this tree was used for ancestral character state reconstructions and correlation analyses.Pivotal results. Leaves directly subtending inflorescences of Periclymenum were free or fused but were rarely partially fused. Fused leaves were ancestral to Periclymenum and were lost in parallel. Leaf fusion was not correlated with inflorescence architecture features, yet inflorescence architecture has become more complex among Periclymenum species.Conclusions. While free leaves are the ancestral condition in the Dipsacales, fused leaves have been gained at least three times and lost at least twice. Given the proximity of fused leaves to reproductive structures, particularly in Lonicera, fused leaves may play a role in protection or in the discovery of flowers and fruits by pollinators and seed dispersers, respectively.
Prabha Amarasinghe, Phuc Pham, Robert Douglas Stone, Nico Cellinese
International Journal of Plant Sciences, Volume 182, pp 682-694; https://doi.org/10.1086/715636

Abstract:
Premise of research. Evergreen forests in eastern South Africa have high biodiversity but are limited in extent and have a highly fragmented distribution. Populations of forest plants are thus geographically isolated, and fine-scale evolutionary studies of these lineages might yield important insights into the history and assembly of the forests themselves. A prior study showed that, despite their morphological diversity, three South African Memecylon taxa in Melastomataceae (Memecylon natalense, M. bachmannii, and M. australissimum) had almost identical nuclear ribosomal spacer sequences. Our study investigates phylogenetic relationships within this clade using multiple samples collected across populations and a next-generation phylogenomic approach.Methodology. We used 87 low-copy nuclear (LCN) loci to examine relationships among these taxa using both concatenated and coalescent methods. We further used LCN loci to estimate phylogenetic networks and single-nucleotide polymorphisms (SNPs) derived from LCN genes for STRUCTURE analysis of South African Memecylon populations. Finally, we employed two approaches (flow cytometry and SNPs) to infer the ploidy levels of these three taxa.Pivotal results. Our investigations showed discordance among gene trees and the species tree and low statistical support for relationships, indicating that species monophyly cannot be recovered from this phylogenomic analysis. Phylogenetic networks and population structures showed that the South African Memecylon clade may be affected by gene flow and reticulate evolution. Flow cytometry and SNP-based estimations provided evidence for polyploidy within this group.Conclusions. We found no evidence of monophyly for species within the South African Memecylon clade, which we infer to be the consequence of reticulation and recent and rapid evolution. More cytological studies and genomic data are needed to elucidate the evolutionary history of this group. Additionally, our study identifies priority populations for conservation within the South African Memecylon clade.
, Félix Forest, Duane Fernandes Lima, Margareth F. Sales, Thais Nogales Vasconcelos, Vanessa G. Staggemeier, Eve Lucas
International Journal of Plant Sciences; https://doi.org/10.1086/715639

Abstract:
Premise of research. Myrcia s.l. is the largest exclusively Neotropical genus of Myrtaceae, comprising about 800 species. This large genus is divided into 10 clades, most of these recently published as sections. One section, Myrcia sect. Myrcia, has 114 species distributed from Mexico to Uruguay, with species diversity centers in the Atlantic Forest, Amazon, and Cerrado. This section includes one of the most difficult to circumscribe species of the Neotropical flora, Myrcia splendens, with the same distribution as the genus and currently with almost 170 synonyms. Phylogenetic relationships and biogeographic patterns in Myrcia sect. Myrcia are examined for the first time using molecular data.Methodology. Phylogenetic inference is based on maximum likelihood and Bayesian analysis of internal transcribed spacer (nuclear), ndhF, psbA-trnH, trnL-trnF, and trnQ-rps16 (plastid) sequences obtained by sequencing a morphologically and geographically representative sample. Phylogenetic relationships, divergence time estimates, and biogeographic patterns are investigated using BEAST and BioGeoBEARS.Pivotal results. Results show that Myrcia sect. Myrcia is monophyletic as morphologically circumscribed. Internal relationships indicate morphologically distinct lineages, but the widespread and taxonomically unruly M. splendens emerges as polyphyletic. Lineages from Central America and the Amazon are sister to multiple dispersals to disparate biomes and subsequent colonization of the Cerrado. Further field and laboratory studies are necessary to understand the extreme morphological plasticity of this section, with a particular focus on improving taxonomic delimitations in M. splendens.Conclusions. This article represents the largest sample of Myrcia sect. Myrcia examined to date. The results presented here demonstrate the monophyly of the section and confirm the nonmonophyly of the widespread M. splendens, with multiple accessions emerging in independent clades from different biomes. The mean estimated age for Myrcia sect. Myrcia is 22.4 mya, and the four clades of focus in this article are estimated to have originated in the Miocene.
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