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Most people can name a mammal or bird that has become extinct in recent centuries, but few can name a recently extinct plant. We present a comprehensive, global analysis of modern extinction in plants. Almost 600 species have become extinct, at a higher rate than background extinction, but almost as many have been erroneously declared extinct and then been rediscovered. Reports of extinction on islands, in the tropics and of shrubs, trees or species with narrow ranges are least likely to be refuted by rediscovery. Plant extinctions endanger other organisms, ecosystems and human well-being, and must be understood for effective conservation planning. An assessment of global extinction in plants shows almost 600 species have become extinct, at a rate higher than background extinction levels, with the highest rates on islands, in the tropics and for shrubs, trees or species with narrow ranges.

Grasses, by their high productivity even under very low pCO2, their ability to survive repeated burning and to tolerate long dry seasons, have transformed the terrestrial biomes in the Neogene and Quaternary. The expansion of grasslands at the cost of biodiverse forest biomes in Madagascar is often postulated as a consequence of the Holocene settlement of the island by humans. However, we show that the Malagasy grass flora has many indications of being ancient with a long local evolutionary history, much predating the Holocene arrival of humans. First, the level of endemism in the Madagascar grass flora is well above the global average for large islands. Second, a survey of many of the more diverse areas indicates that there is a very high spatial and ecological turnover in the grass flora, indicating a high degree of niche specialization. We also find some evidence that there are both recently disturbed and natural stable grasslands: phylogenetic community assembly indicates that recently severely disturbed grasslands are phylogenetically clustered, whereas more undisturbed grasslands tend to be phylogenetically more evenly distributed. From this evidence, it is likely that grass communities existed in Madagascar long before human arrival and so were determined by climate, natural grazing and other natural factors. Humans introduced zebu cattle farming and increased fire frequency, and may have triggered an expansion of the grasslands. Grasses probably played the same role in the modification of the Malagasy environments as elsewhere in the tropics.

Societal impact statement Plants are essential for all life, providing the infrastructure and energy for our ecosystems. A recent report indicates that more than 500 plant species are already presumed extinct and many more could have been lost without anyone being aware, especially in species‐rich areas with high levels of human impact, and where botanical knowledge is poor. Inequality in the availability and accessibility of biodiversity data, professional expertise, and funding interact to produce chronic differences in knowledge between countries. Here, we illustrate this using an example from Madagascar. Understanding these knowledge inequalities will strengthen our ability to improve the situation for people as well as for plants. Summary In order to understand geographic differences in our knowledge of plant extinction, species occurrence knowledge is compared for the grasses (Poaceae) of Madagascar and the British Isles. Poaceae are a useful model system for exploring extinction because they are globally diverse and present interesting characteristics compared with plants as a whole: grasses have a similar species description curve and percentage assessed as threatened, but they have broader and more continental distribution ranges. Historical and current factors affecting the documentation of the Malagasy and British floras are reviewed with regard to science funding, human capital, accessibility, and existing records. Knowledge of Poaceae is compared in the light of these constraints. Global patterns of grass diversity are examined and future extinction rates for Malagasy grasses are estimated. Multiple factors interact to shape a set of constraints on species distribution knowledge. The flora of Madagascar has been described largely by foreigners, science funding is external, and Malagasy botanists face difficult challenges. Spatial data for Madagascar are more limited and less even. We demonstrate that unrecorded extinctions are more likely among Malagasy than British and Irish grasses: they were described later, have smaller ranges, and are more threatened. It is possible that extinction rates of Malagasy grasses will increase tenfold in the next century. Differences in our knowledge of the Malagasy and British floras are long‐standing, deep, and perpetuated by numerous modern‐day factors. We urge researchers to understand and acknowledge these differences, and we provide recommendations for future work. Plants are essential for all life, providing the infrastructure and energy for our ecosystems. A recent report indicates that more than 500 plant species are already presumed extinct and many more could have been lost without anyone being aware, especially in species‐rich areas with high levels of human impact, and where botanical knowledge is poor. Inequality in the availability and accessibility of biodiversity data, professional expertise, and funding interact to produce chronic differences in knowledge between countries. Here we illustrate this using an example from Madagascar. Understanding these knowledge inequalities will strengthen our ability to improve the situation for people as well as for plants.

Abstract Background and Aims Diploid and polyploid Urochloa (including Brachiaria, Panicum and Megathyrsus species) C4 tropical forage grasses originating from Africa and now planted worldwide are important for food security and the environment, often being planted in marginal lands. We aimed to characterize the nature of their genomes, the repetitive DNA, and the genome composition of polyploids, leading to a model of the evolutionary pathways within the group including many apomictic species. Methods Some 362 forage grass accessions from international germplasm collections were studied, and ploidy determined using an optimized flow cytometry method. Whole-genome survey sequencing and molecular cytogenetic analysis with in situ hybridization to chromosomes were used to identify chromosomes and genomes in Urochloa accessions belonging to the different agamic complexes. Key Results Genome structures are complex and variable, with multiple ploidies and genome compositions within the species, and no clear geographical patterns. Sequence analysis of nine diploid and polyploid accessions enabled identification of abundant genome-specific repetitive DNA motifs. In situ hybridization with a combination of repetitive DNA and genomic DNA probes, identified evolutionary divergence and allowed us to discriminate the different genomes present in polyploids. Conclusions We suggest a new coherent nomenclature for the genomes present. We develop a model of evolution at the whole-genome level in diploid and polyploid accessions showing processes of grass evolution. We support the retention of narrow species concepts for U. brizantha, U. decumbens, and U. ruziziensis. The results and model will be valuable in making rational choices of parents for new hybrids, assist in use of the germplasm for breeding and selection of Urochloa with improved sustainability and agronomic potential, and will assist in measuring and conserving biodiversity in grasslands. Competing Interest Statement The authors have declared no competing interest.