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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. 

The spiral gingers (Costus L.) are a pantropical genus of herbaceous perennial monocots; the Neotropical clade of Costus radiated rapidly in the past few million years into over 60 species. The Neotropical spiral gingers have a rich history of evolutionary and ecological research that can motivate and inform modern genetic investigations. Here, we present the first two chromosome-level genome assemblies in the genus, for C. pulverulentus and C. lasius, and briefly compare their synteny. We assembled the C. pulverulentus genome from a combination of short-read data, Chicago and Dovetail Hi-C chromatin-proximity sequencing, and alignment with a linkage map. We assembled the C. lasius genome with Pacific Biosciences HiFi long reads and alignment to the C. pulverulentus genome. These two assemblies are the first published genomes for non-cultivated tropical plants. These genomes solidify the spiral gingers as a model system and will facilitate research on the poorly understood genetic basis of tropical plant diversification. 

Abstract The spiral gingers (Costus L.) are a pantropical genus of herbaceous perennial monocots; the Neotropical clade of Costus radiated rapidly in the past few million years into over 60 species. The Neotropical spiral gingers have a rich history of evolutionary and ecological research that can motivate and inform modern genetic investigations. Here, we present the first 2 chromosome-level genome assemblies in the genus, for C. pulverulentus and C. lasius, and briefly compare their synteny. We assembled the C. pulverulentus genome from a combination of short-read data, Chicago and Dovetail Hi-C chromatin-proximity sequencing, and alignment with a linkage map. We annotated the genome by mapping a C. pulverulentus transcriptome and querying mapped transcripts against a protein database. We assembled the C. lasius genome with Pacific Biosciences HiFi long reads and alignment to the C. pulverulentus genome. These 2 assemblies are the first published genomes for non-cultivated tropical plants. These genomes solidify the spiral gingers as a model system and will facilitate research on the poorly understood genetic basis of tropical plant diversification.