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How close relatives maintain species boundaries in sympatry remains a critical question in biodiversity research. Here we introduce Lobelia sect. Lobelia (Campanulaceae) as a useful clade for investigating such questions. Polyphyly within this clade was strongly suspected because many of the 26 species are cross-compatible and show remarkable overlap in distribution, morphology, ecology, and life history. Indeed, the species Lobelia × rogersii has a purported hybrid origin from Lobelia puberula and Lobelia brevifolia, and the well-known cultivar Lobelia × speciosa results from mating between Lobelia siphilitica and Lobelia cardinalis. We carried out a comprehensive evolutionary investigation of Lobelia sect. Lobelia, including phylogenetic inference, divergence time estimates, and population structure analyses using 729 accessions from 193 natural population sites representing 1–13 individuals per population per species. In contrast to expectations, nearly all species were recovered as reciprocally monophyletic with strong topological support and low levels of interspecific gene flow. An exception to this general pattern is observed in the Florida panhandle, where Lobelia glandulosa and Lobelia apalachicolensis co-occur and appear to be actively hybridizing. We conclude that North American Lobelia species are genetically cohesive, despite significant geographic overlap, frequent co-occurrence, morphological similarity, and broad interfertility in artificial crosses. 

Green plants (Viridiplantae) include around 450,000–500,000 species of great diversity and have important roles in terrestrial and aquatic ecosystems. Here, as part of the One Thousand Plant Transcriptomes Initiative, we sequenced the vegetative transcriptomes of 1,124 species that span the diversity of plants in a broad sense (Archaeplastida), including green plants (Viridiplantae), glaucophytes (Glaucophyta) and red algae (Rhodophyta). Our analysis provides a robust phylogenomic framework for examining the evolution of green plants. Most inferred species relationships are well supported across multiple species tree and supermatrix analyses, but discordance among plastid and nuclear gene trees at a few important nodes highlights the complexity of plant genome evolution, including polyploidy, periods of rapid speciation, and extinction. Incomplete sorting of ancestral variation, polyploidization and massive expansions of gene families punctuate the evolutionary history of green plants. Notably, we find that large expansions of gene families preceded the origins of green plants, land plants and vascular plants, whereas whole-genome duplications are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The increasing availability of high-quality plant genome sequences and advances in functional genomics are enabling research on genome evolution across the green tree of life.