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Reconstructing evolutionary trajectories and transitions that have shaped floral diversity relies heavily on the phylogenetic framework on which traits are modelled. In this study, we focus on the angiosperm order Ranunculales, sister to all other eudicots, to unravel higher-level relationships, especially those tied to evolutionary transitions in flower symmetry within the family Papaveraceae. This family presents an astonishing array of floral diversity, with actinomorphic, disymmetric (two perpendicular symmetry axes), and zygomorphic flowers. We generated nuclear and plastid datasets using the Angiosperms353 universal probe set for target capture sequencing (of 353 single-copy nuclear ortholog genes), together with publicly available transcriptome and plastome data mined from open-access online repositories. We relied on the fossil record of the order Ranunculales to date our phylogenies and to establish a timeline of events. Our phylogenomic workflow shows that nuclear-plastid incongruence accompanies topological uncertainties in Ranunculales. A cocktail of incomplete lineage sorting, post-hybridization introgression, and extinction following rapid speciation most likely explain the observed knots in the topology. These knots coincide with major floral symmetry transitions and thus obscure the order of evolutionary events.

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Studies of pollen wall development produce a great deal of morphological data that supplies useful information regarding taxonomy and systematics. We present the exine development of Euptelea and Pteridophyllum, two taxa whose pollen wall development has never previously been studied using transmission electron microscopy. Both genera are representatives of the two earliest-diverging families of the order Ranunculales and their pollen data are important for the diagnosis of the ancestral pollen features in eudicots. Our observations show these genera are defined by having microechinate microreticulate exine ornamentation, perforate tectum, columellate morphology of the infratectum and the existence of a foot layer and endexine. The presence of lamellations is detected during the early stages of development in the nexine of both genera, especially in the apertures. Euptelea presents remains of the primexine layer during the whole maturation process, a very thin foot layer, and a laminate exinous oncus in the apertural region formed by ectexine and endexine elements. Pteridophyllum has a thicker tectum than Euptelea, a continuous foot layer and a thicker endexine. In the apertures, the exinous oncus is formed by islets and granules of endexine, in contrast to the Euptelea apertures. The secretory tapetum produces orbicules in both genera, but they have different morphology and electron-density. Comparisons with pollen data from related orders and families confirm the ancestral states for the pollen of eudicots proposed in previous studies: reticulate and echinate surfaces, columellate infractectum and a thin foot layer relative to the thickness of the ectexine. According to our observations, we propose considering the possibility of a polymorphic state for the aperture number in the ancestor of Ranunculales, and suggest the development of orbicules as the ancestral state in this order.

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BACKGROUND AND AIMS: Fumarioideae (20 genera, 593 species) is a clade of Papaveraceae (Ranunculales) characterized by flowers that are either disymmetric (i.e. two perpendicular planes of bilateral symmetry) or zygomorphic (i.e. one plane of bilateral symmetry). In contrast, the other subfamily of Papaveraceae, Papaveroideae (23 genera, 230 species), has actinomorphic flowers (i.e. more than two planes of symmetry). Understanding of the evolution of floral symmetry in this clade has so far been limited by the lack of a reliable phylogenetic framework. Pteridophyllum (one species) shares similarities with Fumarioideae but has actinomorphic flowers, and the relationships among Pteridophyllum, Papaveroideae and Fumarioideae have remained unclear. This study reassesses the evolution of floral symmetry in Papaveraceae based on new molecular phylogenetic analyses of the family. METHODS: Maximum likelihood, Bayesian and maximum parsimony phylogenetic analyses of Papaveraceae were conducted using six plastid markers and one nuclear marker, sampling Pteridophyllum, 18 (90 %) genera and 73 species of Fumarioideae, 11 (48 %) genera and 11 species of Papaveroideae, and a wide selection of outgroup taxa. Floral characters recorded from the literature were then optimized onto phylogenetic trees to reconstruct ancestral states using parsimony, maximum likelihood and reversible-jump Bayesian approaches. KEY RESULTS: Pteridophyllum is not nested in Fumarioideae. Fumarioideae are monophyletic and Hypecoum (18 species) is the sister group of the remaining genera. Relationships within the core Fumarioideae are well resolved and supported. Dactylicapnos and all zygomorphic genera form a well-supported clade nested among disymmetric taxa. CONCLUSIONS: Disymmetry of the corolla is a synapomorphy of Fumarioideae and is strongly correlated with changes in the androecium and differentiation of middle and inner tepal shape (basal spurs on middle tepals). Zygomorphy subsequently evolved from disymmetry either once (with a reversal in Dactylicapnos) or twice (Capnoides, other zygomorphic Fumarioideae) and appears to be correlated with the loss of one nectar spur.

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