  Citation: Fenu, G.; Lazzaro, L.; Lastrucci, L.; Viciani, D. Persistence of the Strictly Endemic Plants of Forest Margins: The Case of Cirsium alpis-lunae in the Northern Apennines (Italy). Plants 2022, 11, 653. https:// doi.org/10.3390/plants11050653 Academic Editors: Roberta Masin, Ismael Aranda and Fernando Henrique Reboredo Received: 28 January 2022 Accepted: 23 February 2022 Published: 28 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Article Persistence of the Strictly Endemic Plants of Forest Margins: The Case of Cirsium alpis-lunae in the Northern Apennines (Italy) Giuseppe Fenu 1, * , Lorenzo Lazzaro 2 , Lorenzo Lastrucci 3 and Daniele Viciani 2 1 Department of Life and Environmental Sciences, University of Cagliari, Viale S. Ignazio da Laconi 13, 09123 Cagliari, Italy 2 Department of Biology, University of Florence, Via G. La Pira 4, 50121 Florence, Italy; lorenzo.lazzaro@unifi.it (L.L.); daniele.viciani@unifi.it (D.V.) 3 Natural History Museum, Section of Botany, University of Florence, Via G. La Pira 4, 50121 Florence, Italy; lorenzo.lastrucci@unifi.it * Correspondence: gfenu@unica.it Abstract: Narrow endemic plants constitute a pivotal group for conservation, being often reduced to a small contingent of individuals and frequently threatened. However, effective conservation actions require reliable basic information about distribution range, ecological requirements, and population traits. Nevertheless, such knowledge results are incomplete or even completely missing for some neglected or recently described plants, such as Cirsium alpis-lunae, a thistle exclusive to the N-Apennines (Italy). To fill this gap, all sites where C. alpis-lunae grow were monitored, and data on the site and population traits were collected. Our results indicated that this plant is restricted to 16 scattered sites, varied in surface area and number of individuals. Reproductive and juvenile plants showed to be affected by roughly the same variables, in particular the surface of the site, the slope aspect, and the canopy cover. The narrow ecological niche of C. alpis-lunae was mainly determined by the canopy cover, and where coverage increases, the number of individuals decreases. The individuals only grow at forest edges, where the peculiar ecological conditions are limiting factors for the development of forestry cover; some other factors (i.e., high inclination and instability of the substrate) contribute to limiting the development of forestry vegetation and guarantee the persistence of these ecotones. Despite the great difficulties in accessing the sites where this species grows, this study presents, for the first time, a complete picture of the C. alpis-lunae population and yielded important data to identify effective conservation measures. Keywords: Cirsium; edge specialist plant; mountain plant; narrow endemic plant; neglected plant; plant conservation 1. Introduction Population dynamics is an area of science that attempts to provide an explanation for variations over time in the observed size and structure of biological populations [1–4]; determining whether a population is growing or declining is a central issue in conservation biology [5–7]. In a way, all plants face the risk of extinction due to various causes, such as habitat destruction, habitat fragmentation, displacement by or hybridisation with invasive alien species, climate change, and overharvesting for economic purposes [6,8–10]. Plants with extremely restricted distribution ranges are particularly sensitive to these threats because of their narrow distribution and, often, low numbers of populations or individuals. On the other hand, some plant species, generally narrow endemics, by their nature have very small or scattered populations, often extremely adapted to their environment. Since narrow endemic plants are often reduced to a small contingent of individuals or are frequently threatened, they constitute a pivotal group for conservation [6,11,12]. Regardless, Plants 2022, 11, 653. https://doi.org/10.3390/plants11050653 https://www.mdpi.com/journal/plants