Background and aims – The intensive botanical prospections carried out in Gabon since the publication of the national checklist in 2006 have resulted in c. 34 300 new specimens (amounting to 30% of all collections made in the country) and an annual increase of 25 species in average. As a result, 5175 species of vascular plants are now recorded from Gabon, of which 650 are considered endemic. However, most of the recent discoveries have not yet been published. This paper is the first of a series documenting additions to the flora of Gabon, and new records of poorly known species. It concerns specifically new records from the Lower Ogooué Ramsar site, the third largest delta of Africa, and certainly the most intact, which includes 80% of the country’s wetlands and a wide variety of other habitats.Methods – The new records presented here come essentially from fieldwork conducted in Gabon between 2008 and 2016 by the authors and colleagues. Further information comes from the study of herbarium specimens in BR, BRLU, K, LBV, MO, P and WAG. For each species, information on distribution and ecology is given, and the studied Gabonese collections listed. In case of rare or range-restricted species, collections from other countries are also listed, and a distribution map is provided, as well as an evaluation of the conservation status based on the categories and criteria of the IUCN Red List.Key results – We report 18 additions to the flora of Gabon, including four genera new to the country (Capparis, Gisekia, Hoffmanniella and Leptochloa) and the first records of the neotropical Justicia secunda being naturalised in tropical Africa. New distribution records are also provided for 16 rare Gabonese endemics or near-endemics. Some species are also newly reported from Cameroon (Cissus leemansii, Salacia coronata) and Equatorial Guinea (Cissus leemansii, C. louisii, Lychnodiscus grandifolius, Placodiscus resendeanus, Rutidea gabonensis, Uvaria bipindensis). Two species, which were reported in the 2006 checklist based on misidentifications, are excluded from the Gabonese flora.

Although the Congo River Basin contains the second largest tropical rainforest in the world, tropical Africa has fewer tree census plots than tropical Asia or America. Thus, more data are needed to describe species richness and diversity. We conducted a tree census to reveal the species richness and composition of a middle-altitude forest in Moukalaba-Doudou National Park, Gabon. We set a 150×150-m plot (2°3.2'S, 10°25.0'E) at an altitude of 220 m. All trees >10 cm in diameter at breast height (DBH) were marked, and the DBH of each was measured. We recorded 988 trees, 692 (70.0 %) of which were fully identified to 63 species. Among the rest, 267 trees (27.0 %) were classified into 27 genera, and 22 trees (2.23 %) were classified into 10 families. The 6 most common species accounted for 50.6 % (500 trees) of the total number of trees: Dichostemma glaucescens (Euphorbiaceae), Diospyros sp. 1 (Ebenaceae), Strombosia pustulata (Olacaceae), Synsepalum longecuneatum (Sapotaceae), Staudtia kamerunensis var. gabonensis (Myristicaceae) and Pausinystalia macroceras (Rubiaceae). The remaining 86 species had <10 trees per ha, and 42 species of these had <1 tree per ha on average. These low-density species reflect a high-diversity forest.

Endemism is one of the most important concepts in biogeography and is often used to guide biodiversity conservation, yet our understanding of the determinants of endemism in many biodiverse tropical regions is limited. This is true for western Central Africa, a region with one of the highest levels of plant diversity in tropical Africa, where endemism is poorly documented. This study examines the Gabonese Area of Endemism (GAE) and explores the main characteristics and determinants of its vascular plant endemism with regard to taxonomy, growth form, habitat, distribution, and range size. We compiled a comprehensive, verified specimen database of vascular plant taxa restricted to the GAE, comprising 19,876 occurrences of 1145 species and infraspecific taxa, and we characterized the habitat and habit for each taxon. We then calculated the proportion of taxa in the regional flora that are endemic to the GAE. A Wilcoxon rank-sum test was used to investigate range size among endemic taxa exhibiting different growth forms, and Fisher exact tests were used to explore the association between their habit and habitat, and to test the distribution of these attributes among higher-level taxa and growth forms compared to patterns in the regional flora as a whole. We found that endemic taxa represent ca. 13% of the GAE flora, and that the rate of endemism varies considerably among taxonomic groups and growth forms. Endemism is highest among shrubs (22%) and lowest in herbs (8%), especially monocotyledons (e.g., 5% among Poales). Most endemic taxa grow preferentially in forest habitats, the dominant vegetation type of the region. Endemic trees, which structure forest ecosystems, have significantly larger ranges than endemic herbs, climbers, and shrubs. About 17% of the flora of Gabon is endemic or subendemic to the country. Our results show that the dispersal capacity of taxa and the biogeographical history of the region appear to be critical factors in explaining differences in the rate of endemism among growth forms and taxonomic groups. Our findings also highlight the benefits of carefully building a comprehensive and verified database for studying rare and range-restricted plants, and they underscore the necessity to strengthen botanical exploration throughout western Central Africa in order to develop improved and better-informed conservation strategies.

Background – The number of vascular plant species known to occur in Gabon rises quickly due to renewed collecting and inventory activities, often in little-known or previously uncollected areas.Methods – Herbarium material from BR, BRLU and WAG was studied.Results – Two genera (Alloteropsis, Entolasia), eleven species and one variety of grasses are recorded from Gabon for the first time (Alloteropsis paniculata, Cenchrus echinatus, Elionurus platypus, Entolasia olivacea, Eragrostis patens, Hyparrhenia diplandra var. mutica, Leersia triandra, Loudetia annua, Oryza longistaminata, Rottboellia purpurascens, Sacciolepis africana and Setaria geminata), while information on two erroneous species reports is provided. This brings the total number of grass species known to occur in Gabon to 190. Finally, new records of four rare species (Elionurus hensii, Guaduella macrostachys, Paratheria prostrata and Puelia schumanniana) are discussed.

Background and aims – Podostemaceae is a family of strictly aquatic plants found in rapids and waterfalls. Despite a recent treatment in the Flore du Gabon, the family remained poorly known, with no major studies including Gabonese collections, and almost no targeted inventories since 1966. We present the first large-scale inventory of this family in Gabon, targeting Podostemaceae throughout the country, providing new additions to the flora of Gabon and many new records of poorly known species. Material and methods – Fieldwork was conducted in Gabon between 2017 and 2021. The collected specimens were primarily preserved in ethanol with associated silica gel-preserved material and photographs. Material available at BR, BRLU, LBV, MO, P, WAG, and Z/ZT was examined. For each species, information on distribution and ecology is presented, as well as a distribution map in Gabon. Key results – The 500 newly collected specimens represent 91.4% of all known collections of Podostemaceae from Gabon. Three taxa are newly recorded for the country, including one genus (Inversodicraea tenax, Ledermanniella schlechteri, and Saxicolella nana). New distribution records are also presented for 13 little-known species. Four taxa are excluded from the Gabonese flora (the genus Dicraeanthus, Inversodicraea ledermannii, Ledermanniella sanagaensis, and Macropodiella garrettii). To date, 20 species belonging to five different genera are known to occur in Gabon. A new combination is proposed for Ledermanniella nicolasii, and Inversodicraea tanzaniensis is now considered as a synonym of Inversodicraea tenax.