Foliar micromorphology with emphasis on the trichomes diversity and its taxonomic relevance in selected tribes of Asteraceae from Hainan Island

The Asteraceae is one of the most taxonomically complex, medicinally and economically important family among the angiosperms. Therefore, this study aims to evaluate the leaf anatomical features to correctly identify the Asteraceae species of Hainan Island. Scanning electron microscopy was used to investigate various micro epidermal traits. Leaf micromorphology of all the species was characterized, visualized and compared using UPGMA Cluster analysis (CA), chord diagram and ridgeline plot. Generally, the trichomes were divided into two main categories, glandular trichomes (GTs) and non-glandular trichomes (NGTs). The GTs was further classified into capitate, subsessile and sessile capitate. The NGTs were classified into long falcate, short conical, lipidote and filiform. The stomata were mostly anomocytic and anisocytic sometimes mixed with tetracytic type. However, there are varied assortments of trichomes and stomata with transitions among them especially in their type, frequency and number of cells. The trichomes and stomata can be successfully used for the delimitation of the genera within the family. The statistical analysis can help in better understanding of the results that characterized, visualized and compared the leaf anatomical traits of the Asteraceae taxa. Overall, these traits collectively have a significant taxonomic potential to identify and define species boundaries at the tribe and generic levels and can be used as an additional tool for regrouping taxa within Asteraceae.