What are some of the future directions we see for research on the genetic attributes of polyploids? The general mode of formation of polyploids remains unknown; research into the factors that produce unreduced gametes and bring them together certainly is warranted. Additional studies, both theoretical and empirical, are needed to address expectations of inbreeding depression and outcrossing rates. Furthermore, the levels of gene flow among populations, especially those populations of separate origin, are unknown. Regarding genome rearrangements, how extensive are they within an individual or race? How widespread are they among species? How quickly do such rearrangements occur? Do populations of separate origin exhibit the same or different rearrangements? Finally, are basal angiosperms and homosporous pteridophytes with high chromosome numbers of ancient polyploid origin? If so, what can we learn about gene silencing from these plants? How extensive has gene silencing been, and is there evidence for the cooption of duplicated genes for new function? The study of polyploidy is a dynamic and open area of research, ranging from molecular genetic comparisons to population genetics, with important implications for the biology and evolution of the majority of plant species.

We thank Kent Holsinger and an anonymous reviewer for helpful comments on the manuscript. This research was supported, in part, by the National Science Foundation. This work is dedicated to the memory of G. Ledyard Stebbins.

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Front Matter (R1-R8)

Introduction: Variation and evolution in plants and microorganisms: Toward a new synthesis 50 years after Stebbins (6941-6944)

G. Ledyard Stebbins (1906-2000): An appreciation (6945-6946)

Solution to Darwin's dilemma: Discovery of the missing Precambrian record of life (6947-6953)

The chimeric eukaryote: Origin of the nucleus from the karyomastigont in amitochondriate protists (6954-6959)

Dynamic evolution of plant mitochondrial genomes: Mobile genes and introns and highly variable mutation rates (6960-6966)

The evolution of RNA viruses: A population genetics view (6967-6973)

Effects of passage history and sampling bias on phylogenetic reconstruction of human influenza A evolution (6974-6980)

Bacteria are different: Observations, interpretations, speculations, and opinions about the mechanisms of adaptive evolution in prokaryotes (6981-6985)

Evolution of RNA editing in trypanosome mitochondria (6986-6993)

Population structure and recent evolution of Plasmodium flaciparum (6994-7001)

Transponsons and genome evolution in plants (7002-7007)

Maize as a model for the evolution of plant nuclear genomes (7008-7015)

Flower color variation: A model for the experimental study of evolution (7016-7023)

Gene genealogies and population variation in plants (7024-7029)

Toward a new synthesis: Major evolutionary trends in the angiosperm fossil record (7030-7036)

Reproductive systems and evolution in vascular plants (7037-7042)

Hybridization as a stimulus for the evolution of invasiveness of plants? (7043-7050)

The role of genetic and genomic attributes in the success of polyploids (7051-7060)