On the presence of uncommon stylar glandular trichomes in Asteraceae: A study in <i>Kaunia</i> R. M. King and H. Rob. (Oxylobinae, Eupatorieae)

Abstract

Premise of research. Glands on the styles of Asteraceae are uncommon. They are reported in <i>Kaunia</i> for the first time. Glandular trichomes of plants are involved in the synthesis of secondary metabolites. In <i>Kaunia</i>, secondary compounds with medicinal cytotoxic, antitumor activity, and sensitizing capacity were previously identified. In this frame, a deeper knowledge of glandular trichomes could shed light on the productivity of medicinal substances in <i>Kaunia</i>. The potential taxonomic and ecological value of stylar glandular trichomes in <i>Kaunia</i> is also explored together with trichome secretion phases throughout the floral developmental stages. Methodology. Herbarium specimens and flowers fixed in FAA of 10 species of <i>Kaunia</i> were analyzed. Flowers in different developmental stages were studied to observe the secretory phases of stylar trichomes. A histochemical test was carried out to detect sesquiterpene lactones on stylar glandular trichomes. Pivotal results. Glandular trichomes were detected on the ventral face of style branches in eight species of <i>Kaunia</i> in all floral stages analyzed. The stylar trichomes observed were mostly found in secretory or early postsecretory phases in the most immature floral stages. The histochemical test in stylar trichomes was positive for sesquiterpene lactones. Conclusions. The presence of stylar glandular trichomes provides valuable new evidence for the identification and characterization of <i>Kaunia</i>. Within the Eupatorieae, the presence of stylar glandular trichomes could be interpreted as taxonomically valuable at the rank of genus. Our finding of sesquiterpene lactones is in agreement with the presence of Guaianolides and Germacranolides previously isolated in <i>Kaunia</i>. Apparently, the secretion of trichomes is completed before the opening of the corolla. The glands on styles of <i>Kaunia</i> could be the most internal barrier to herbivores that could flank outer floral structures during pollen and style development.