Madagascar’s biota is hyperdiverse and includes exceptional levels of endemicity. We review the current state of knowledge on Madagascar’s past and current terrestrial and freshwater biodiversity by compiling and presenting comprehensive data on species diversity, endemism, and rates of species description and human uses, in addition to presenting an updated and simplified map of vegetation types. We report a substantial increase of records and species new to science in recent years; however, the diversity and evolution of many groups remain practically unknown (e.g., fungi and most invertebrates). Digitization efforts are increasing the resolution of species richness patterns and we highlight the crucial role of field- and collections-based research for advancing biodiversity knowledge and identifying gaps in our understanding, particularly as species richness corresponds closely to collection effort. Phylogenetic diversity patterns mirror that of species richness and endemism in most of the analyzed groups. We highlight humid forests as centers of diversity and endemism because of their role as refugia and centers of recent and rapid radiations. However, the distinct endemism of other areas, such as the grassland-woodland mosaic of the Central Highlands and the spiny forest of the southwest, is also biologically important despite lower species richness. The documented uses of Malagasy biodiversity are manifold, with much potential for the uncovering of new useful traits for food, medicine, and climate mitigation. The data presented here showcase Madagascar as a unique “living laboratory” for our understanding of evolution and the complex interactions between people and nature. The gathering and analysis of biodiversity data must continue and accelerate if we are to fully understand and safeguard this unique subset of Earth’s biodiversity.

Madagascar’s unique biota is heavily affected by human activity and is under intense threat. Here, we review the current state of knowledge on the conservation status of Madagascar’s terrestrial and freshwater biodiversity by presenting data and analyses on documented and predicted species-level conservation statuses, the most prevalent and relevant threats, ex situ collections and programs, and the coverage and comprehensiveness of protected areas. The existing terrestrial protected area network in Madagascar covers 10.4% of its land area and includes at least part of the range of the majority of described native species of vertebrates with known distributions (97.1% of freshwater fishes, amphibians, reptiles, birds, and mammals combined) and plants (67.7%). The overall figures are higher for threatened species (97.7% of threatened vertebrates and 79.6% of threatened plants occurring within at least one protected area). International Union for Conservation of Nature (IUCN) Red List assessments and Bayesian neural network analyses for plants identify overexploitation of biological resources and unsustainable agriculture as the most prominent threats to biodiversity. We highlight five opportunities for action at multiple levels to ensure that conservation and ecological restoration objectives, programs, and activities take account of complex underlying and interacting factors and produce tangible benefits for the biodiversity and people of Madagascar.

Summary: This paper is the fourth part of the taxonomic revision of the genus Phyllanthus in Madagascar and the Comoro Islands. Here we treat Pseudogomphidium Ralim. & Cable sect. nov. consisting of nine species that we misplaced in the subgenus Gomphidium (Baill.) G.L.Webster in our previous paper. Two species are new to science: Phyllanthus razakamalalae Ralim. & Cable, sp. nov. and P. ankirindrensis Ralim. & Cable, sp. nov. We also treat three unplaced species: P. analamerae Leandri, P. coluteoides Müll.Arg. and P. vergens Baill. An identification key, descriptions, distribution maps and IUCN Red List assessments are provided.

Societal Impact Statement: Plants and agricultural practices are an integral part of human food systems and well‐being. Here, an example of an ethnobotanical research approach is provided to increase our understanding of the relationship between plants and human activities in Madagascar, where the agricultural sector is the local economy basis. This research examines weeds of the Poaceae family, assessing their recognition and societal impacts, and quantifying farmers' perception of the Poaceae weed's status in cropping systems. A better understanding of farmers' weed knowledge will strengthen our ability to inclusively support rural highland Malagasy food systems, incorporating science with traditional knowledge.Summary: Research on the perceptions and knowledge of Poaceae weeds was conducted in three areas of Madagascar's central highlands: Itremo massif, Ambohidray village and Vakinankaratra region. This work aims to identify the best‐known species and understand their roles in crop and livestock systems. Additionally, it presents detailed data on Digitaria species. The approach was based on field surveys and farmer's interviews, with plant voucher specimens and photographs to facilitate identification. Relative frequency of citations, confidence interval, and use values indexes were calculated to assess cultural significance. We carried out 111 interviews, where 87 taxa were mentioned, of which 51 are Poaceae, including 11 Digitaria species. Farmers classify the Poaceae weeds in three ways: their impacts on agricultural activities, use category and vegetative growth patterns, the latter especially significant for Digitaria. Locally common grasses are perceived as weeds when they are abundant and cause yield loss. The most damaging species is Digitaria humbertii, confirmed by half of the interviews. More than 40% of the farmers use Poaceae weeds in composting, more than 20% as fodder, and more than 8% as medicine. Overall, 67% of the species mentioned are judged useful. The diversity of useful species and the associated indigenous knowledge is important to the local communities, but, weeds are still perceived as negative generally. The Poaceae are overall neglected in Malagasy ethnobotany, and an in‐depth analysis of farmer knowledge is needed. The data obtained will be useful for future studies and the conservation of agrobiodiversity, especially endemic species that are not widely known.

SUMMARY: 1) Research Aims — Loudetia simplex is a common and dominant species throughout grassland ecosystems in mainland Africa and Madagascar. It is highly polymorphic, often classified as two taxa endemic to Madagascar: L. simplex subsp. stipoides and L. madagascariensis . A better understanding of the inter- and intra-specific variation between these taxa and its contributing environmental factors could improve our understanding of the history of Madagascar’s grasslands. 2) Methods — The taxonomic status of L. simplex subsp. stipoides and L. madagascariensis was evaluated by morphometric analyses of 119 herbarium specimens. Species distribution modelling was used to determine the most important environmental factors underlying the L. simplex distribution in Madagascar versus other African grasslands. We investigated if L. simplex in Madagascar could be predicted by distributions across mainland Africa with niche overlap analyses. 3) Key Result — African and Malagasy species exhibited variation potentially associated with environment. Specimens from northern and western Madagascar were taller with smaller spikelets than those from Southern Africa and central Madagascar. Loudetia simplex typically occurred in cooler temperatures with high precipitation and pronounced seasonality, but taller populations were found in warmer conditions. Projecting ecological niches of Southern Africa and East Tropical Africa onto Madagascar demonstrates much of the present distribution in the Central Highlands is expected from other natural African grasslands. 4) Key Point — Malagasy and African individuals represent a single species, and the Malagasy species can be considered as a synonym of L. simplex. Distribution models are congruent with pre-human presence of grasslands in Madagascar. SOCIETAL IMPACT STATEMENT: Understanding dominant species like Loudetia simplex is necessary to understand the fire-driven grassy ecosystems they create. In Madagascar, grasslands are considered a low-value ecosystem despite their unique biodiversity and crucial importance as zebu rangeland. Only 1.8% of Madagascar’s grasslands are protected despite facing similar threats to forests and biodiversity loss. This study of common grasses will support the management of protected areas by providing information on resource management of vulnerable open ecosystems in Madagascar. Distribution models of common grass species and clear taxonomic classification can help land management stakeholders identify natural grasslands versus degraded forests.