A key goal of evolutionary biology is to understand the processes that drive and maintain biodiversity across heterogeneous landscapes. My dissertation leverages a highly polymorphic system in Calochortus, C. venustus, to identify and to interpret the evolutionary significance of geographical patterns of floral trait variation, genetic diversity, range evolution, and the genetic mechanisms underlying climatic adaptation utilizing comparative methods from population genetics and genomics. Using a comparative transcriptomic approach, I identify candidate genes responsible for variation in trichome density and placement across floral syndromes in the genus.The first chapter is designed to test the hypothesis that various floral forms in the highly polymorphic C. venustus function as a single species. I collected and imaged 174 individuals from the wild and generated restriction-site associated DNA sequencing (RAD-Seq) reads. I analyzed single nucleotide polymorphism (SNP) data to characterize genetic diversity among populations, quantify gene flow between populations and among individuals of alternative floral phenotypes, estimate ancestral range evolution, and document regional floral trait distributions within and between populations. I found contrasting patterns of morphological and genetic diversity and found evidence that the striking floral diversity of C. venustus is indeed functioning as a polymorphic species. Genetic data support an evolutionary history consistent with C. venustus functioning as a ring species, adding to the small number of known ring species, with parallel morphological convergence at the northern end of coastal and inland lineages. In the second chapter, I leverage SNP data in C. venustus to develop a multi-pronged population genomic analysis aimed at identifying loci putatively responsible for local climatic adaptation. I identified targets of selection by distinguishing loci that are outliers to population structure and use genotype-environment associations to detect loci under selection from each of nine climatic variables that capture latitudinal and longitudinal variation in the abiotic environment. I found evidence of ecological specialization at the molecular level, including SNPs located in genes that are associated with cold stress, heat, water deprivation, salt stress, and root development. SNPs show parallel trends in allelic similarity across two latitudinal transects indicating adaptation to northern climates, as well as divergent genetic evolution across longitude suggesting adaptation to either coastal or inland habitats. I present empirical evidence that allele frequencies for SNPs under selection track climatic clines. The goal of the third chapter is to identify candidate genes that regulate the location and density of floral trichomes in the genus Calochortus. Trichomes are thought to influence pollinator attraction, herbivore exclusion, and regulation of temperature. I developed and analyzed floral gene expression profiles using comparative RNA-Sequencing for three species representing three floral syndromes. Differential gene expression between three developmental stages and between sepals and petals revealed a core set of trichome genes in Calochortus. The core genes are a subset of key trichome genes in model systems and likely play a conserved role in trichome development across monocots as well. Variation in the developmental timing of expression across species and variation in expression of paralogs may indicate mechanisms underlying the high variability in trichome development across the genus.