Evolutionary diversification of new caledonian Araucaria

New Caledonia is a global biodiversity hotspot. Hypotheses for its biotic richness suggest either that the island is a ‘museum’ for an old Gondwana biota or alternatively it has developed following relatively recent long distance dispersal and in situ radiation. The conifer genus Araucaria (Araucariaceae) comprises 19 species globally with 13 endemic to this island. With a typically Gondwanan distribution, Araucaria is particularly well suited to testing alternative biogeographic hypotheses concerning the origins of New Caledonian biota. We derived phylogenetic estimates using 11 plastid and rDNA ITS2 sequence data for a complete sampling of Araucaria (including multiple accessions of each of the 13 New Caledonian Araucaria species). In addition, we developed a dataset comprising 4 plastid regions for a wider taxon sample to facilitate fossil based molecular dating. Following statistical analyses to identify a credible and internally consistent set of fossil constraints, divergence times estimated using a Bayesian relaxed clock approach were contrasted with geological scenarios to explore the biogeographic history of Araucaria. The phylogenetic data resolve relationships within Araucariaceae and among the main lineages in Araucaria, but provide limited resolution within the monophyletic New Caledonian species group. Divergence time estimates suggest a Late Cretaceous-Cenozoic radiation of extant Araucaria and a Neogene radiation of the New Caledonian lineage. A molecular timescale for the evolution of Araucariaceae supports a relatively recent radiation, and suggests that earlier (pre-Cenozoic) fossil types assigned to Araucaria may have affinities elsewhere in Araucariaceae. While additional data will be required to adequately resolve relationships among the New Caledonian species, their recent origin is consistent with overwater dispersal following Eocene emersion of New Caledonia but is too old to support a single dispersal from Australia to Norfolk Island for the radiation of the Pacific Araucaria sect. Eutacta clade.Mai Lan Kranitz, Edward Biffin, Alexandra Clark, Michelle L. Hollingsworth, Markus Ruhsam, Martin F. Gardner, Philip Thomas, Robert R. Mill, Richard A. Ennos, Myriam Gaudeul, Andrew J. Lowe, Peter M. Hollingswort

An overview of extant conifer evolution from the perspective of the fossil record

Premise of the Study Conifers are an important living seed plant lineage with an extensive fossil record spanning more than 300 million years. The group therefore provides an excellent opportunity to explore congruence and conflict between dated molecular phylogenies and the fossil record. Methods We surveyed the current state of knowledge in conifer phylogenetics to present a new time‐calibrated molecular tree that samples ~90% of extant species diversity. We compared phylogenetic relationships and estimated divergence ages in this new phylogeny with the paleobotanical record, focusing on clades that are species‐rich and well known from fossils. Key Results Molecular topologies and estimated divergence ages largely agree with the fossil record in Cupressaceae, conflict with it in Araucariaceae, and are ambiguous in Pinaceae and Podocarpaceae. Molecular phylogenies provide insights into some fundamental questions in conifer evolution, such as the origin of their seed cones, but using them to reconstruct the evolutionary history of specific traits can be challenging. Conclusions Molecular phylogenies are useful for answering deep questions in conifer evolution if they depend on understanding relationships among extant lineages. Because of extinction, however, molecular datasets poorly sample diversity from periods much earlier than the Late Cretaceous. This fundamentally limits their utility for understanding deep patterns of character evolution and resolving the overall pattern of conifer phylogeny

Leaf surface development and the plant fossil record: stomatal patterning in Bennettitales

Stomata play a critical ecological role as an interface between the plant and its environment. Although the guard-cell pair is highly conserved in land plants, the development and patterning of surrounding epidermal cells follow predictable pathways in different taxa that are increasingly well understood following recent advances in the developmental genetics of the plant epidermis in model taxa. Similarly, other aspects of leaf development and evolution are benefiting from a molecular?genetic approach. Applying this understanding to extinct taxa known only from fossils requires use of extensive comparative morphological data to infer ?fossil fingerprints? of developmental evolution (a ?palaeo-evo-devo? perspective). The seed-plant order Bennettitales, which flourished through the Mesozoic but became extinct in the Late Cretaceous, displayed a consistent and highly unusual combination of epidermal traits, despite their diverse leaf morphology. Based on morphological evidence (including possession of flower-like structures), bennettites are widely inferred to be closely related to angiosperms and hence inform our understanding of early angiosperm evolution. Fossil bennettites ? even purely vegetative material ? can be readily identified by a combination of epidermal features, including distinctive cuticular guard-cell thickenings, lobed abaxial epidermal cells (?puzzle cells?), transverse orientation of stomata perpendicular to the leaf axis, and a pair of lateral subsidiary cells adjacent to each guard-cell pair (termed paracytic stomata). Here, we review these traits and compare them with analogous features in living taxa, aiming to identify homologous ? and hence phylogenetically informative ? character states and to increase understanding of developmental mechanisms in land plants. We propose a range of models addressing different aspects of the bennettite epidermis. The lobed abaxial epidermal cells indicate adaxial?abaxial leaf polarity and associated differentiated mesophyll that could have optimised photosynthesis. The typical transverse orientation of the stomata probably resulted from leaf expansion similar to that of a broad-leaved monocot such as Lapageria, but radically different from that of broad-leafed eudicots such as Arabidopsis. Finally, the developmental origin of the paired lateral subsidiary cells ? whether they are mesogene cells derived from the same cell lineage as the guard-mother cell, as in some eudicots, or perigene cells derived from an adjacent cell lineage, as in grasses ? represents an unusually lineage-specific and well-characterised developmental trait. We identify a close similarity between the paracytic stomata of Bennettitales and the ?living fossil? Gnetum, strongly indicating that (as in Gnetum) the pair of lateral subsidiary cells of bennettites are both mesogene cells. Together, these features allow us to infer development in this diverse and relatively derived lineage that co-existed with the earliest recognisable angiosperms, and suggest that the use of these characters in phylogeny reconstruction requires revision

Eocene Araucaria

Premise: Eocene floras of Patagonia document biotic response to the final separation of Gondwana. The conifer genus Araucaria, distributed worldwide during the Mesozoic, has a disjunct extant distribution between South America and Australasia. Fossils assigned to Australasian Araucaria Sect. Eutacta usually are represented by isolated organs, making diagnosis difficult. Araucaria pichileufensis E.W. Berry, from the middle Eocene Río Pichileufú (RP) site in Argentine Patagonia, was originally placed in Sect. Eutacta and later reported from the early Eocene Laguna del Hunco (LH) locality. However, the relationship of A. pichileufensis to Sect. Eutacta and the conspecificity of the Araucaria material among these Patagonian floras have not been tested using modern methods. Methods: We review the type material of A. pichileufensis alongside large (n = 192) new fossil collections of Araucaria from LH and RP, including multi-organ preservation of leafy branches, ovuliferous complexes, and pollen cones. We use a total evidence phylogenetic analysis to analyze relationships of the fossils to Sect. Eutacta. Results: We describe Araucaria huncoensis sp. nov. from LH and improve the whole-plant concept for Araucaria pichileufensis from RP. The two species respectively resolve in the crown and stem of Sect. Eutacta. Conclusions: Our results confirm the presence and indicate the survival of Sect. Eutacta in South America during early Antarctic separation. The exceptionally complete fossils significantly predate several molecular age estimates for crown Eutacta. The differentiation of two Araucaria species demonstrates conifer turnover during climate change and initial South American isolation from the early to middle Eocene.Fil: Rossetto Harris, Gabriella. State University of Pennsylvania; Estados UnidosFil: Wilf, Peter. State University of Pennsylvania; Estados UnidosFil: Escapa, Ignacio Hernán. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Andruchow Colombo, Ana. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin