Pappus morphology and heterocarpy in Stevia (Eupatorieae, Asteraceae): A systematic study of cypselae diversity and geographic distribution

The genus Stevia (Asteraceae, Eupatorieae) is widely distributed across the Americas and exhibits remarkable diversity in cypsela morphology and pappus structure. The variation in pappus types, including both homocarpic and heterocarpic species, plays a critical role in species delimitation within the genus. In this study, we investigate the morphology of cypselae and pappus across a diverse sample of Stevia species, emphasizing the systematic significance of pappus variation. Species were analyzed using light and scanning electron microscopy, focusing on key traits such as pappus structure, the presence of heterocarpy, and the arrangement of cypselae within the capitulum. Eight distinct pappus types were identified and described as fundamental morphological patterns. Additionally, species distribution maps are provided to illustrate the geographical patterns associated with these pappus types. Our findings contribute to a deeper understanding of morphological diversity within Stevia and underscore the importance of pappus variation in species identification and taxonomic classification.