Fothergilla

Abstract: Fothergilla (Hamamelidaceae) consists of Fothergilla gardenii (4x) from the coastal plains of the southeastern USA, F. major (6x) from the piedmont and mountains of the same region, and a few allopatric diploid populations of unknown taxonomic status. The objective of this study was to explore the relationships of the polyploid species with the diploid plants. Genotyping by sequencing (GBS) was applied to generate genome-wide molecular markers for phylogenetic and genetic structure analyses of 36 accessions of Fothergilla. Sanger sequencing of three plastid and one nuclear regions provided data for comparison with GBS-based results. Phylogenetic outcomes were compared using data from different sequencing runs and different software workflows. The different data sets showed substantial differences in inferred phylogenies, but all supported a genetically distinct 6x F. major and two lineages of the diploid populations closely associated with the 4x F. gardenii. We hypothesize that the 4x F. gardenii originated through hybridization between the Gulf coastal 2x and an extinct (or undiscovered) 2x lineage, followed by backcrosses to the Atlantic coastal 2x before chromosome doubling, and the 6x F. major also originated from the “extinct” 2x lineage. Alternative scenarios are possible but are not as well supported. The origins and divergence of the polyploid species likely occurred during the Pleistocene cycles of glaciation, although fossil evidence indicates the genus might have existed for a much longer time with a wider past distribution. Our study demonstrates the power of combining GBS data with Sanger sequencing in reconstructing the evolutionary network of polyploid lineages.

Abstract: Corylopsis reedae Radtke, Pigg et Wehr sp. nov. and Fothergilla malloryi Radtke, Pigg et Wehr sp. nov. (Hamamelidaceae) are described from the lower Eocene (49–50 million years ago) Republic flora of northeastern Washington State. Corylopsis reedae is the first unequivocal fossil leaf report of Corylopsis Siebold & Zucc. (cv. Winter Hazel). The species is based on a single specimen that is 1.9 cm wide, preserved for 3.4 cm in length and estimated to be ca. 4 cm long, with an asymmetrical base and teeth that are concave apical, straight basal, with simple apices. The fossil leaf is remarkably similar to extant Corylopsis, with prominent compound agrophic veins; strong, straight secondaries; and closely spaced, ladder‐rung‐like, opposite to alternate percurrent tertiaries at right angles to the secondaries. Today this genus occurs only in Asia, but the fossil record, primarily of seeds, indicates it was widely distributed in North America and Europe during the Tertiary. Fothergilla malloryi documents conclu...

Abstract: The diverse Early to Middle Eocene Okanagan Highlands floras of south central British Columbia and northeastern Washington reflect a time of rapid evolution and the early radiation of many dicot families that are currently significant elements of temperate floras. Recent studies of the Republic, Washington flora (Klondike Mountain Formation) and related Okanagan floras in British Columbia have documented both the earliest, and sometimes the only, known fossil occurrences of genera. Today many once more widespread taxa are restricted, particularly to Asian and (or) eastern North American refugia. Examples include members of the families Betulaceae (birch, hazelnut), Rosaceae (rose), Hamamelidaceae (witch hazel), and the endemic Asian family Trochodendraceae. Earliest occurrences are noted for Neviusia (Rosaceae), Trochodendron (Trochodendraceae), Corylus and Carpinus (both Betulaceae). The first unequivocal leaf records of Corylopsis and Fothergilla (both Hamamelidaceae), and two new Eocene species of the extinct fruit Palaeocarpinus (Betulaceae) are also recognized. Today, Trochodendron and Corylopsis are restricted to Asia, whereas Neviusia and Fothergilla , genera with close Asian relatives, occur only in North America. Corylus johnsonii from Republic is most similar to the extant Asian species C. heterophylla , C. wangii , and C. ferox . Neviusia leaves from One Mile Creek near Princeton, British Columbia are more similar to N. cliftonii , an endemic from Mount Shasta, California, than to N. alabamensis of southeastern North America. A better documentation of the Okanagan Highlands floras is essential to our understanding of the evolution of North American temperate floras and the nature of Asian – North American disjunct taxa.