Societal Impact Statement
Plant genomes exhibit spectacular diversity in size, composition, and complexity, and although we suspect that this diversity is related to the equally spectacular diversity of plant form and function, this link is still poorly understood. Plant genomes carry signatures of evolutionary history, whole-genome duplication, population processes, and more, and we are just learning how to read this historical information from appropriate genetic markers. But plant genomes are not merely chroniclers of past evolutionary change: they are dynamic, evolving entities in their own right, driving changes in plant chemistry, morphology, ecology, and more. Here, we describe how plant genomes have been harnessed for studies of plant phylogeny and diversification, with examples spanning all green plants, a clade of nearly half a million species spanning nearly a billion years of evolutionary time. Then focusing on angiosperms, we suggest how the process of whole-genome duplication (polyploidy) has driven, and continues to drive, major innovations in morphology, stress response, and more. Together, these perspectives will begin to reveal how genomic change can lead to novelty and diversity at the organismal level. Finally, we review how little we actually know about plant genomes, given that assembled genome sequences exist for fewer than 1% of all plant species—a major shortcoming as we seek to meet societal challenges of food security, the need for new medicines, and conservation of species in response to climate change.