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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. 

Abstract Inclusion of edaphic conditions in biogeographical studies typically provides a better fit and deeper understanding of plant distributions. Increased reliance on soil data calls for easily accessible data layers providing continuous soil predictions worldwide. Although SoilGrids provides a potentially useful source of predicted soil data for biogeographic applications, its accuracy for estimating the soil characteristics experienced by individuals in small‐scale populations is unclear. We used a biogeographic sampling approach to obtain soil samples from 212 sites across the midwestern and eastern United States, sampling only at sites where there was a population of one of the 22 species inLobeliasect.Lobelia. We analyzed six physical and chemical characteristics in our samples and compared them with predicted values from SoilGrids. Across all sites and species, soil texture variables (clay, silt, sand) were better predicted by SoilGrids (R²: .25–.46) than were soil chemistry variables (carbon and nitrogen,R² ≤ .01; pH,R²: .19). While SoilGrids predictions rarely matched actual field values for any variable, we were able to recover qualitative patterns relating species means and population‐level plant characteristics to soil texture and pH. Rank order of species mean values from SoilGrids and direct measures were much more consistent for soil texture (Spearmanr_S = .74–.84; allp < .0001) and pH (r_S = .61,p = .002) than for carbon and nitrogen (p > .35). Within the speciesL. siphilitica, a significant association, known from field measurements, between soil texture and population sex ratios could be detected using SoilGrids data, but only with large numbers of sites. Our results suggest that modeled soil texture values can be used with caution in biogeographic applications, such as species distribution modeling, but that soil carbon and nitrogen contents are currently unreliable, at least in the region studied here.