Documenting the flora of a diversity hotspot: Richard Thomas Lowe (1802–1874) and his botanical exploration of Madeira island Sandra Mesquita, 1 Mark Carine, 2 Cristina Castel-Branco 1 & Miguel Menezes de Sequeira 3 1 CEABN - InBio, Instituto Superiorde Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349 - 017 Lisboa, Portugal 2 Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom 3 InBio, ResearchNetwork in Biodiversity and Evolutionary Biology, CIBIO-Azores, Madeira Botanic Group (GBM), Universidade da Madeira, Campus da Penteada, 9000-390 Funchal, Portugal Address for correspondence: Sandra Mesquita, mesquita.s@gmail.com DOI https://doi.org/10.1002/tax.12661 Abstract Oceanic island floras often exhibit remarkable concentrations of endemic diversity, provide spectacular examples of rapid evolutionary radiations and harbour floras under significant threat due to anthropogenic pressures. They have attracted the interest of biologists for centuries, but their floras continue to yield new taxa and, at a global scale, the extent of their plant diversity remains imperfectly known. Both natural characteristics and historical factors have shaped the development of knowledge of island floras. In this paper, we investigate the approach of Richard Thomas Lowe (1802–1874), to documenting the flora of Madeira island in the North Atlantic. Lowe collected abundantly in Madeira between 1826 and 1873, resulting in severalworks on Madeira’ s flora, pub- lished from the 1830s. At a time when taxonomic research on island floras was often based on limited collections made during brief expeditions, Lowe’ s research on the flora, spanning almost half a century, was exceptional. In this study, 2579 herbarium specimens collected by Lowe were georeferenced and used to investigate temporal, spatial and taxonomic patterns in Lowe’ s collecting activities. We also examine the distribution of specimens by Lowe to other botanists. Some biases are evident in Lowe’ s collecting efforts, with steep slopes under-sampled and coastal sites over-sampled. These reflect constraints imposed by topography and transport links. These limitations aside, Lowe’ s work on the Madeiran flora was conducted in a systematic manner, resulting in a comprehensive study of the entire flora. His approach was distinctly modern: he gathered and studied all available information in herbaria and in the pub- lished and unpublished writings from earlier visitors; his initial fieldwork was conducted widely to gain knowledge of all habitats and their floras; later fieldwork focussed on less-explored and most promising areas; duplicates were sent to other botanists, facilitating taxonomic exchanges on critical taxa; and his later fieldwork focussed on plant groups where taxonomic problems had been detected. As a result of Lowe’ s sustained and systematic approach, he is the single most prolific contributor to the study of Madeira’ s endemic flora. His approach is a model to documenting island floras still relevant today. Areas poorly sampled by Lowewere areas that were difficult to access, which also protected them from anthropic destructive activities and allowed them to serve as refuges for endemic flora. Those areas deserve particular attention in efforts to complete the survey of Madeira’ s plant diversity, using technological ad- vancements such as drones to prospect areas that are otherwise still largely inaccessible. Keywords georeferencing historical data; historical herbaria; history of botany; island flora; Macaronesia Supporting Information may be found online in the Supporting Information section at the end of the article. ■ INTRODUCTION The volcanic oceanic archipelago of Madeira in the North Atlantic (Fig. 1) has a flora typical of oceanic islands more gen- erally: a remarkable concentration of endemic diversity (172 species in 801 km 2 ; see Appendix 1), examples of rapid evolu- tionary radiations (Whittaker & Fernández-Palacios, 2006) and significant threats to the survival of the flora from anthropogenic pressures with 50% of endemics considered threatened (Jardim & al., 2006). Moreover, many endemic taxa were certainly ex- tinct before the first naturalists arrived to the island and thus can’ t be accounted for (Menezes de Sequeira & al., 2013). Madeira is also an island where new taxa continue to be dis- covered and described. Joppa & al. (2011) suggested that island floras are well documented and, in the case of Madeira, the explo- ration and description of its flora by natural historians has a his- tory spanning more than 350 years (Menezes de Sequeira & al., 2010). Nevertheless, seven endemic taxa—Echium portosan- tense J.A.Carvalho & al., Holcus pintodasilvae M.Seq. & Cas- trov., Musschia isambertoi M.Seq. & al., Pericallis menezesii R.Jardim & al., Sonchus parathalassius J.G.Costa ex R.Jardim & M.Seq., Teucrium francoi M.Seq. & al. and Viola sequeirae Capelo & al.—all rare, have been described as new to the Ma- deira archipelago in the last 20 years (4% of the endemic flora), an observation consistent with the findings from a survey of biologists working on oceanic islands that knowledge of the taxonomy, distribution and threat status of plants on oceanic islands remains insufficient (Caujapé-Castells & al., 2010). Article history: Received: 26 Feb 2021 | returned for (first) revision: 29 Apr 2021 | (last) revision received: 17 Oct 2021 | accepted: 19 Oct 2021 Associate Editor: Javier Francisco-Ortega | © 2022 International Association for Plant Taxonomy. Version of Record 1 TAXON 00 (00) • 1–16 Mesquita & al. • Documenting the flora of a diversity hotspot RESEARCH ARTICLE