Phylogenomic Discordance in Plant Systematics

Book excerpt: Phylogenetics often uncovers contradicting hypotheses regarding the relationships within the same group of organisms, a phenomenon known since the beginning of the molecular systematics era. While, historically, single marker-based analyses produced discordance, nowadays entire cellular genomes or portions of the same genomic compartment conflict with others or the rest, respectively. In contrast to the beginning of the molecular systematics era, when adding markers and taxa offered a way out of systematic errors, genome inference-based incongruences cannot be addressed and explained easily. Disagreeing phylogenomic hypotheses might originate from various evolutionary processes, including but not limited to hybridization or incomplete lineage sorting, thereby leading to gene tree-versus species tree-associated discrepancies. Today, this can be expanded to genome discordance, where phylogenomic signals of organellar genomes (plastid, mitochondrial) and the nuclear genome disagree due to intrinsically different coalescent paths or phenomena like organelle capture.