Hidden in plain sight: Distinguishing a narrow endemic Clarkia from an allopolyploid derivative despite morphological and ecological overlap

Polyploidy is a common mechanism of speciation in flowering plants, but its influence on morphology and ecology is often uncertain. Allopolyploidy in the genus Clarkia has led to several widespread species that overlap geographically and morphologically with diploid progenitors, causing taxonomic challenges. One example is C. rhomboidea, an allopolyploid that frequently co-occurs with its diploid progenitor, C. virgata , a narrow endemic. Using flow cytometry and a greenhouse common garden, we evaluated the ploidy of new and existing records and identified floral traits that can distinguish the species. We then used two diagnostic floral traits to determine the frequency of misclassifications in occurrence databases. We also conducted studies of phenology in the field. Last, we asked whether the geographic range and niche (breadth and overlap) were influenced by misclassifications. Where their ranges overlap, we found that 45% of C. virgata records were C. rhomboidea while 6% of C. rhomboidea records were C. virgata . Two diagnostic traits, anther angle and protandry, jointly distinguished the two species but are not present in species’ descriptions or taxonomic keys. Correction of records increased the elevational range of C. virgata but had minimal effects on niche. We documented earlier flowering of C. rhomboidea in occurrence records and a sympatric site, but high niche overlap. Finally, we tripled the number of verified C. virgata records (from 37 to 116). Our study provides new characters that distinguish the two species and shows that misclassifications have been common and consequential for understanding the ecology and rarity of the diploid.