Irritation. Based on our detailed morphological and anatomical analyses, and within the functional aspects observed, we concluded that the glandular trichomes in Fischeria and Matelea can indeed be classified as stinging. Hence, Apocynaceae could be the seventh family members for which this kind of trichome has been reported. We also compiled info on stinging trichomes in all households of angiosperms. Their phylogenetic distribution indicates that they have evolved no less than 12 times throughout angiosperm evolution and may represent an evolutionary convergence of plant defense against herbivory. Key phrases: glandular trichomes; plant defense; evolutionary convergence; anatomy; secretion; ApocynaceaePublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.1. Introduction Flowering plants have several types of internal and external secretory structures for protection against herbivory. The initial secretory structures to evolve had been straightforward, consisting of single cells, e.g., idioblasts and laticifers. Much more complicated internal structures, for example secretory ducts and cavities, appeared later in the evolutionary history of angiosperms. Apparently, the glandular trichomes evolved a lot more not too long ago. They have extra complex secretory processes and dynamics of interaction with the atmosphere as they may be external structures [1,2]. Amongst glandular trichomes, the stinging ones stand out for their type of defense function against herbivory. These trichomes are rare, found in only some angiosperm families, and their secretion is composed of a myriad of chemical substances . Stinging trichomes are in a position to puncture the skin by way of their needle-shaped apical cells that have stiffened walls. When the tip of the trichome is broken, its contents are QX-222 Autophagy injected beneath the skin [4,5]. The secretion produces an allergic reaction within the skinCopyright: 2021 by the authors. Licensee MDPI, Basel, Switzerland. This short article is definitely an open access report distributed beneath the terms and circumstances from the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Plants 2021, 10, 2324. https://doi.org/10.3390/plantshttps://www.mdpi.com/journal/plantsPlants 2021, 10,two of(dermatitis), causing a variety of symptoms from a mild irritation to death, based around the plant species and contacting animal involved [1,5,6]. These trichomes have restricted occurrence, traditionally described as occurring in four families of eudicots: Euphorbiaceae, Hydrophyllaceae, Loasaceae and Urticaceae [5,6]. Together with the APG IV  update, which integrated adjustments in Boraginales, genera with stinging trichomes are now also placed in two more households, i.e., Heliotropiaceae and Namaceae, resulting in six households possessing such a trait. In these families, they’re commonly comprised of an elongated secretory cell set on a multicellular pedestal. The secretory cell features a round basal portion and an acuminate apical portion that terminates with a needle-like tip . On the other hand, two species of Apocynaceae from the Atlantic Rainforest are also called “nettle” by some neighborhood dwellers and brought on skin irritation for the duration of fieldwork performed in the course of our prior research, therefore indicating the doable existence of stinging trichomes within this household. Only glandular trichomes have already been described in Apocynaceae, where they may be rare and reported for several genera of Asclepiadoideae: Araujia, Cynanchum (“Sarcostemma”), Dischidia; Fischeria, Vc-seco-DUBA Drug-Linker Conjugates for ADC Gongrone.