Plants provide fundamental support systems for life on Earth and are the basis for all terrestrial ecosystems; a decline in plant diversity will be detrimental to all other groups of organisms including humans. Decline in plant diversity has been hard to quantify, due to the huge numbers of known and yet to be discovered species and the lack of an adequate baseline assessment of extinction risk against which to track changes. The biodiversity of many remote parts of the world remains poorly known, and the rate of new assessments of extinction risk for individual plant species approximates the rate at which new plant species are described. Thus the question ‘How threatened are plants?’ is still very difficult to answer accurately. While completing assessments for each species of plant remains a distant prospect, by assessing a randomly selected sample of species the Sampled Red List Index for Plants gives, for the first time, an accurate view of how threatened plants are across the world. It represents the first key phase of ongoing efforts to monitor the status of the world’s plants. More than 20% of plant species assessed are threatened with extinction, and the habitat with the most threatened species is overwhelmingly tropical rain forest, where the greatest threat to plants is anthropogenic habitat conversion, for arable and livestock agriculture, and harvesting of natural resources. Gymnosperms (e.g. conifers and cycads) are the most threatened group, while a third of plant species included in this study have yet to receive an assessment or are so poorly known that we cannot yet ascertain whether they are threatened or not. This study provides a baseline assessment from which trends in the status of plant biodiversity can be measured and periodically reassessed.

Our investigations seek to illustrate the use of fluorescence spectral deconvolution to characterize multiple partitioning sites for aromatic chromophores within aqueous and reverse micelles. The spatial distribution of solutes within micellar systems is dictated by a variety of noncovalent interactions. To probe for multiple partitioning microenvironments, we use the aromatic fluorophore Prodan with its extensive solubility in a range of media and its appreciable spectral sensitivity to the polarity of its surroundings. We conduct a systematic study of the partitioning of Prodan in aqueous micellar systems with anionic, cationic, zwitterionic, and nonionic surfactant headgroups and in reverse micellar systems with both anionic and cationic surfactant headgroups. By deconvoluting the overall Prodan fluorescence emission spectrum into a sum of overlapping Gaussian functions, the principal microenvironments of the Prodan molecules may be ascertained. Fluorescence data are consistent with the location of Prodan in a variety of sites, including partitionings that may be influenced by electrostatic, hydrophobic, dipolar, and cation−π interactions in both aqueous and reverse micelles.

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