Gunnerales

Abstract: Phylogenetic relationships among many lineages of angiosperms have been clarified via the analysis of large molecular data sets However, with a data set of three genes (18S rDNA, rbcL, and atpB), relationships among lineages of core eudicots (Berberidopsidales, Caryophyllales, Gunnerales, Santalales, Saxifragales, asterids, rosids) remain essentially unresolved We added 26S rDNA sequences to a three-gene matrix for 201 eudicots (8430 base pair aligned nucleotides per taxon) Parsimony analyses provided moderate (84%) jackknife support for Gunnerales, which comprise the two enigmatic families Gunneraceae and Myrothamnaceae, as sister to all other core eudicots This position of Gunnerales has important implications for floral evolution A dimerous or trimerous perianth is frequently encountered in early-diverging eudicots (eg, Buxaceae, Proteales, Ranunculales, Trochodendraceae), whereas in core eudicots, pentamery predominates Significantly, dimery is found in Gunneraceae and perhaps Myrothamnaceae (the merosity of the latter has also been interpreted as labile) Parsimony reconstructions of perianth merosity demonstrate lability among early-diverging eudicots and further indicate that a dimerous perianth could be the immediate precursor to the pentamerous condition characteristic of core eudicots Thus, the developmental canalization that yielded the pentamerous condition of core eudicots occurred after the node leading to Gunnerales

Abstract: Recent molecular phylogenetic studies have shown that the Gunnerales, including Gunnera and Myrothamnus, form a clade, sister to other core eudicots. This systematic position puts Gunnera in a pivotal position regarding the evolution of morphological characters in eudicots. In particular, the dimerous flower organization of Gunnera has recently been considered precursor to the pentamerous condition found in most core eudicots. In order to understand the role of Gunnera in the flower evolution of core eudicots, new detailed studies of the flowers of Gunnera are needed. In this study, the flower ontogeny and morphology of Gunnera monoica and G. dentata as well as of G. macrophylla were studied with SEM. The new observations are compared with previous studies of G. manicata and G. herteri. The first four species have dimerous perfect or staminate flowers with two small median sepals, followed by two large petals opposite the two stamens. In G. herteri, the staminate flowers are reduced to single stamens. In ...

Abstract: Recent phylogenetic analyses revealed a grade with Ranunculales, Sabiales, Proteales, Trochodendrales, and Buxales as first branching eudicots, with the respective positions of Proteales and Sabiales still lacking statistical confidence As previous analyses of conserved plastid genes remain inconclusive, we aimed to use and evaluate a representative set of plastid introns (group I: trnL; group II: petD, rpl16, trnK) and intergenic spacers (trnL-F, petB-petD, atpB-rbcL, rps3-rpl16) in comparison to the rapidly evolving matK and slowly evolving atpB and rbcL genes Overall patterns of microstructural mutations converged across genomic regions, underscoring the existence of a general mutational pattern throughout the plastid genome Phylogenetic signal differed strongly between functionally and structurally different genomic regions and was highest in matK, followed by spacers, then group II and group I introns The more conserved atpB and rbcL coding regions showed distinctly lower phylogenetic information content Parsimony, maximum likelihood, and Bayesian phylogenetic analyses based on the combined dataset of non-coding and rapidly evolving regions (>14 000 aligned characters) converged to a backbone topology of eudicots with Ranunculales branching first, a Proteales–Sabiales clade second, followed by Trochodendrales and Buxales Gunnerales generally appeared as sister to all remaining core eudicots with maximum support Our results show that a small number of intron and spacer sequences allow similar insights into phylogenetic relationships of eudicots compared to datasets of many combined genes The non-coding proportion of the plastid genome thus can be considered an important information source for plastid phylogenomics