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    Background The algal flora of the western group of the Azores archipelago (Islands of Flores and Corvo) has attracted the interest of many researchers on numerous past occasions (such as Drouët 1866; Trelease 1897; Gain 1914; Schmidt 1929, 1931; Azevedo et al. 1990; Fralick & Hehre 1990; Neto & Azevedo 1990; Neto & Baldwin 1990; Neto 1996, 1997, 1999; Tittley & Neto, 1996, 2000, 2005, 2006; Azevedo 1998, 1999; Tittley et al. 1998; Dionísio et al. 2008; Neto et al. 2008). Despite this interest, the macroalgal flora of the Islands cannot be described as well-known with the published information reflecting limited collections preformed in short term visits by scientists. To overcome this, a thorough investigation, encompassing collections and presence data recording, has been undertaken for both the littoral and sublittoral regions, down to a depth of approximately 40 m, covering a relatively large area on both Islands (approximately 143 km2 for Flores and 17 km2 for Corvo). This paper lists the resultant taxonomic records and provides information on species ecology and occurrence around both these Islands, thereby improving the knowledge of the Azorean macroalgal flora at both local and regional scales. New information For the Island of Flores, a total of 1687 specimens (including some taxa identified only to genus level) belonging to 196 taxa of macroalgae are registered, comprising 120 Rhodophyta, 35 Chlorophyta and 41 Ochrophyta (Phaeophyceae). Of these taxa, 128 were identified to species level (80 Rhodophyta, 22 Chlorophyta and 26 Ochrophyta), encompassing 37 new records for the Island (20 Rhodophyta, 6 Chlorophyta and 11 Ochrophyta); two Macaronesian endemics (Laurencia viridis Gil-Rodríguez & Haroun and Millerella tinerfensis (Seoane-Camba) S.M.Boo & J.M.Rico); six introduced (the Rhodophyta Asparagopsis armata Harvey, Neoizziella divaricata (C.K.Tseng) S.-M.Lin, S.-Y.Yang & Huisman, and Symphyocladia marchantioides (Harvey) Falkenberg; the Chlorophyta Codium fragile subsp. fragile (Suringar) Hariot; and the Ochrophyta Hydroclathrus tilesii (Endlicher) Santiañez & M.J.Wynne, and Papenfussiella kuromo (Yendo) Inagaki); and 14 species of uncertain status (10 Rhodophyta, 2 Chlorophyta and 2 Ochrophyta). For the Island of Corvo, a total of 390 specimens distributed in 56 taxa of macroalgae are registered, comprising 30 Rhodophyta, 9 Chlorophyta and 17 Ochrophyta (Phaeophyceae). Whilst a number of taxa were identified only to the genus level, 43 were identified to species level (22 Rhodophyta, 8 Chlorophyta and 13 Ochrophyta), comprising 22 new records for the Island (9 Rhodophyta, 4 Chlorophyta and 9 Ochrophyta), two introduced species (the Rhodophyta Asparagopsis armata and the Chlorophyta Codium fragile subsp. fragile, and seven species of uncertain status (5 Rhodophyta and 2 Ochrophyta). Introduction The Azorean algal flora, considered cosmopolitan, with species shared with Macaronesia, North Africa, the Mediterranean Sea, Atlantic Europe and America (Tittley 2003, Tittley & Neto 2006, Wallenstein et al. 2009), is relatively rich when compared to that of other remote oceanic Islands (Neto et al. 2005, Tittley & Neto 2005, Wallenstein et al. 2009). Around 400 species of marine macroalgae have, to date, been recorded for the isolated mid-Atlantic Azores archipelago (Freitas et al. 2019). These authors, based on extensive analysis encompassing data on brachyurans, polychaetes, gastropods, echinoderms, coastal fishes and macroalgae, suggested that the Azores should be a biogeographical entity of its own and proposed a redefinition of the Lusitanian biogeographical province, in which they recognised four ecoregions: the South European Atlantic Shelf, the Saharan Upwelling, the Azores ecoregion, and a new ecoregion herein named Webbnesia, which comprises the archipelagos of Madeira, Selvagens and the Canary Islands. In their paper comparing the Azorean algal flora to that of the new Webbnesia region, they reported that the Canary Islands, with 689 species of marine macroalgae, are by far the most diverse archipelago, followed by the Azores (405), Madeira (396) and Cabo Verde (333). The Selvagens are the least diverse one (295 species). It is worth mentioning that the published information reflects data from only a few of the nine Azorean Islands, since not all of them have been adequately investigated. In the Azores archipelago, São Miguel is by far the Island with the largest amount of research dedicated to the study of its algal flora. The total number of algal species is, at the moment, 260, a number that is likely to increase due to ongoing research by authors of the present paper. Most of the remaining Islands have received less attention. To overcome this, and improve the understanding of the archipelago’s macroalgal flora, research has been conducted over the past three decades on all the Islands. Data on the Islands of Pico, Graciosa and Terceira is already available on the recently published papers by Neto et al. (2020b, c, d). To provide a better understanding of the archipelago’s seaweed flora, a long term research programme of study has been undertaken, mainly by local investigators into the marine macroalgae flora on several of the less studied Azorean Islands. The present paper presents both physical and occurrence data, and information gathered from surveys undertaken on Flores and Corvo Islands mainly by the Island Aquatic Research Group of the Azorean Biodiversity Centre of the University of the Azores (Link: the BIOISLE, Biodiversity and Islands Research Group of CIBIO-Açores at the University of the Azores (Link:, and the OKEANOS Centre of the University of the Azores (Link: In these surveys particular attention was given to the small filamentous and thin sheet-like species that are often short-lived and fast-growing, and usually very difficult to identify in the wild, without the aid of a microscope and specialised literature in the laboratory. The present paper aims to provide a valuable marine biological tool for research on systematics, diversity and conservation, biological monitoring, climate change and ecology for academics, students, government, private organizations and the general public. Purpose: In this paper we present taxonomic records of macroalgae recorded from the Islands of Flores and Corvo and provide general information on their occurrence and distribution. By doing this, we are contributing to address several biodiversity shortfalls (see Cardoso et al. 2011, Hortal et al. 2015), namely the need to catalogue the Azorean macroalgae (Linnean shortfall) and improve the current information on their local and regional geographic distribution (Wallacean shortfall), as well as on species abundance and dynamics in space (Prestonian shortfall).