Critical reexamination of palynological characters used to delimit Asclepiadaceae in comparison to the molecular phylogeny obtained from plastid matK sequences

Evolution of 101 Apocynaceae plastomes and phylogenetic implications

Apocynaceae are one of the ten species-richest angiosperm families. However, the backbone phylogeny of the family is yet less well supported, and the evolution of plastome structure has not been thoroughly studied for the whole family. Herein, a total of 101 complete plastomes including 35 newly sequenced, 24 reassembled from public raw data and the rest from the NCBI GenBank database, representing 26 of 27 tribes of Apocynaceae, were used for comparative plastome analysis. Phylogenetic analyses were conducted using a combined plastid data matrix of 77 protein-coding genes from 162 taxa, encompassing all tribes and 41 of 49 subtribes of Apocynaceae. Plastome lengths ranged from 150,897 bp in Apocynum venetum to 178,616 bp in Hoya exilis. Six types of boundaries between the inverted repeat (IR) regions and single copy (SC) regions were identified. Different sizes of IR expansion were found in three lineages, including Alyxieae, Ceropegieae and Marsdenieae, suggesting multiple expansion events of the IRs over the SC regions in Apocynaceae. The IR regions of Marsdenieae evolved in two ways: expansion towards the large single copy (LSC) region in Lygisma + Stephanotis + Ruehssia + Gymnema (Cosmopolitan clade), and expansion towards both LSC and small single copy (SSC) region in Dischidia-Hoya alliance and Marsdenia (Asia-Pacific clade). Six coding genes and five non-coding regions were identified as highly variable, including accD, ccsA-ndhD, clpP, matK, ndhF, ndhG-ndhI, trnG(GCC)-trnfM(CAU), trnH(GUG)-psbA, trnY(GUA)-trnE(UUC), ycf1, and ycf2. Maximum likelihood and Bayesian phylogenetic analyses resulted in nearly identical tree topologies and produced a well-resolved backbone comprising 15 consecutive dichotomies that subdivided Apocynaceae into 15 clades. The subfamily Periplocoideae were embedded in the Apocynoid grade and were sister to the Echiteae-Odontadenieae-Mesechiteae clade with high support values. Three tribes (Melodineae, Vinceae, and Willughbeieae), the subtribe Amphineuriinae, and four genera (Beaumontia, Ceropegia, Hoya, and Stephanotis) were not resolved as monophyletic. Our work sheds light on the backbone phylogenetic relationships in the family Apocynaceae and offers insights into the evolution of Apocynaceae plastomes using the most densely sampled plastome dataset to date.

Light and scanning electron microscopic characterization of pollen grains of some wetland angiosperms from India

Pollen grains of 58 wetland species of angiosperms belonging to 17 families, growing in different wetlands of Sub-Himalayan biodiversity hotspots, Northern Bengal and lower Gangetic plains, India were investigated during a 4-year span of 2015-2019. Freshly collected anthers were processed through the acetolysis method and the obtained pollen grains were accurately studied under LM and SEM and properly photographed. Different attributes viz. shape, size, aperture type and exine ornamentation of pollen grains served as consistent features were used for authentic identification of the studied species. To study the phylogeny of pollen grains, characters like polarity, symmetry, aperture and exine sculpturing were found most significant for species segregation. Investigated pollen grains were mostly prolate-spheroidal, spheroidal or triangular, rarely prolate or elongated, exine psilate, granulate, reticulate or microechinate type. Most of the observable aperture of pollen grains of studied species were colporate, colpate and porate, while ulcerate and inaperturate grains were also observed in the studied aquatic members of the families Cyperaceae and Potamogetonaceae. All the gathered data were further statistically analyzed through ANOVA, PCA and Pearson Correlation Matrix to understand the interrelationship among the species. The permanent slides of identified pollen grains were deposited at the herbarium of North Bengal University [NBU] for future references.

Taxonomic Implication of Integrated Chemical, Morphological, and Anatomical Attributes of Leaves of Eight Apocynaceae Taxa

Up to now, the taxonomic conflict of the Apocynaceae family has attracted the attention of scientists and researchers worldwide. Recently, this family was divided into five subfamilies. The present study aims to investigate the implication of interlacing macro-, micro-morphological, anatomical, and chemical characteristics of the leaves of eight Apocynaceae plants (Adenium obesum, Dipladenia boliviensis, Carissacarandas, Nerium oleander, Asclepias curassavica, Calotropisprocera, Acokanthera oblongifolia, and Thevetia neriifolia), and to provide valuable taxonomic differentiation of these species. The macro-morphological investigation includes shape, apex, base, and venation of leaves, while the micro-morphological study includes leaf epidermal cells, stomata, and trichomes. The anatomical features of the leaf blade were studied by scanning electron microscope (SEM). Additionally, the chemical composition of the silylated methanolic extract was analyzed by Gas chromatography–mass spectroscopy (GC-MS). Sixty-three compounds were characterized from the silylated extracts of the eight plants, where quinic acid, sucrose, D-pinitol, and D-(−)-fructopyranose were determined as major compounds. The Principal Component Analysis (PCA) based on the chemical composition revealed a significant chemical correlation among all species with the presence of sugars and amino acids, as well as phenolic acids and iridoid glycosides. The cluster analysis, based on all merged characters, showed that the eight species can be categorized into three clusters. The first cluster comprises A.obesum, A. curassavica, and T. neriifolia, while the second cluster contains D. boliviensis, N. oleander, A. oblongifolia, and C. carandas, and the third cluster consists of C. procera alone. This cluster revealed some similarities to the recent classification of Apocynaceae, while it showed inconsistency regarding A.obesum, C. procera, and N. oleander. Due to the obtained inconsistent data and observed variation among the studied species, further study is recommended for more characterization of these species, based on additional parameters, including molecular characteristics, particularly A.obesum, C. procera, and N. oleander.

Development and evolution of extreme synorganization in angiosperm flowers and diversity: a comparison of Apocynaceae and Orchidaceae

BACKGROUND AND AIMS

Apocynaceae and Orchidaceae are two angiosperm families with extreme flower synorganization. They are unrelated, the former in eudicots, the latter in monocots, but they converge in the formation of pollinia and pollinaria, which do not occur in any other angiosperm family, and for which extreme synorganization of floral organs is a precondition. In each family extensive studies on flower development and evolution have been performed; however, newer comparative studies focusing on flower synorganization and involving both families together are lacking.

SCOPE

For this study an extensive search through the morphological literature has been conducted. Based on this and my own studies on flowers in various Apocynaceae and Orchidaceae and complex flowers in other angiosperms with scanning electron microscopy and with microtome section series, a review on convergent floral traits in flower development and architecture in the two families is presented.

KEY FINDINGS

There is a tendency of protracted development of synorganized parts in Apocynaceae and Orchidaceae (development of synorganization of two or more organs begins earlier the more accentuated it is at anthesis). Synorganization (or complexity) also paves the way for novel structures. One of the most conspicuous such novel structures in Apocynaceae is the corona, which is not the product of synorganization of existing organs; however, it is probably enhanced by synorganization of other, existing, floral parts. In contrast to synorganized parts, the corona appears developmentally late.

CONCLUSIONS

Synorganization of floral organs may lead to a large number of convergences in clades that are only very distantly related. The convergences that have been highlighted in this comparative study should be developmentally investigated directly in parallel in future studies.

Molecular phylogeny of Vincetoxicum (Apocynaceae-Asclepiadoideae) based on the nucleotide sequences of cpDNA and nrDNA

Molecular phylogenetic analyses of Vincetoxicum and Tylophora (Apocynaceae-Asclepiadoideae) were conducted based on the nucleotide sequences of cpDNA (two intergenic spacers of trnL (UAA)-trnF (GAA) and psbA-trnH and three introns, i.e., atpF, trnG (UCC) and trnL (UAA)), and nrDNA (ITS and ETS regions). Our phylogenetic analysis revealed two monophyletic groups; one consisted of seven taxa of Tylophora and Vincetoxicum inamoenum, Vincetoxicum magnificum and Vincetoxicum macrophyllum (Clade I) and the other consisted of 17 accessions of Vincetoxicum (Clade II). The monophyly of the genus Vincetoxicum was not supported. Although many nucleotide substitutions were observed in Clade I, the genetic differentiation within Clade II was small. Low genetic diversification but considerable morphological divergence suggests that the species in Clade II had undergone rapid diversification. Although most species in Clade I have tiny flowers, those in Clade II have larger and more nectariferous ones. Thus, we hypothesized that the rapid morphological radiation in Clade II may have been due to the gaining of floral characters such as large flowers and large amounts of nectar corresponding to diverse pollinators.

A survey of tricolpate (eudicot) phylogenetic relationships

The phylogenetic structure of the tricolpate clade (or eudicots) is presented through a survey of their major subclades, each of which is briefly characterized. The tricolpate clade was first recognized in 1989 and has received extensive phylogenetic study. Its major subclades, recognized at ordinal and familial ranks, are now apparent. Ordinal and many other suprafamilial clades are briefly diagnosed, i.e., the putative phenotypic synapomorphies for each major clade of tricolpates are listed, and the support for the monophyly of each clade is assessed, mainly through citation of the pertinent molecular phylogenetic literature. The classification of the Angiosperm Phylogeny Group (APG II) expresses the current state of our knowledge of phylogenetic relationships among tricolpates, and many of the major tricolpate clades can be diagnosed morphologically.

Rapid expansion of microsatellite sequences in pines

Microsatellite persistence time and evolutionary change was studied among five species of pines, which included a pair of closely related species (Pinus sylvestris and Pinus resinosa) in the subgenus Pinus, their relative Pinus radiata, and another closely related species pair (Pinus strobus and Pinus lambertiana) in the subgenus Strobus. The effective population sizes of these species are known to have ranged from the very small bottlenecks of P. resinosa to vast populations of P. sylvestris. This background allowed us to place the microsatellite evolution in a well-defined phylogenetic setting. Of 30 loci originating from P. strobus and P. radiata, we were able to consistently amplify 4 in most of the these pine species. These priming sites had been conserved for over 100 Myr. The four microsatellites were sequenced in the five species. Flanking sequences were compared to establish that the loci were orthologous. All microsatellites had persisted in these species, despite very different population sizes. We found a recent microsatellite duplication: a closely related pair of loci in P. strobus, where the other four species had just one locus. On two independent occasions, the repeat area of this same microsatellite (locus RPS 105a/b) had grown from a very low repeat number to 15 or 17 in the last 10-25 Myr. Other parts of the same compound microsatellite had remained virtually unchanged. Locus PR 4.6 is known to be polymorphic in both P. radiata and P. sylvestris, but the polymorphism in the two species is due to different motifs. The very large pine genomes are highly repetitive, and microsatellite loci also occur as gene families.