Leaf cover: An ecological perspective of the peculiar type and arrangement of trichomes in Kaunia (Eupatorieae, Asteraceae)

Abstract

Premise of the Research. While carrying out a taxonomic revision of Kaunia, uncommon types of trichomes and arrangement of trichomes on the leaves of K. gynoxymorpha and K. pachanoi were observed. Moreover, the trichome arrangement is not usual for either Kaunia or most of Eupatorieae. In this study, we aim to describe the leaf blade trichomes and indumentum in these two species and discuss, together with other anatomical characteristics, their ecological role, and potential adaptation to arid environments. Methodology. We used traditional light microscopy, scanning electron microscopy (SEM), and fluorescence microscopy to examine leaf blade anatomical characteristics. Besides, we carried out histochemical techniques on the leaves of both studied species to determine the presence of cutinized cell walls which may influence apoplastic water flow in trichomes. Pivotal Results. Our results show two-armed trichomes in Kaunia gynoxymorpha that are unusual in the tribe Eupatorieae. The arrangement of glandular and non-glandular leaf trichomes of the two studied species in tufts of 3 to 10 trichomes, sunken in surface crypts, is also uncommon. Conclusions. These tufts of trichomes and other anatomical and histochemical evidence suggest that non-glandular trichomes and their arrangement in tufts in Kaunia gynoxymorpha and K. pachanoi provide adaptive advantages by combining physical, mechanical, and biochemical functions, thus protecting plants against drought and high light intensity among other adverse conditions.