Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects.We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives. Geosphere-Biosphere Program (IGBP) and DIVERSITAS, the TRY database (TRY-not an acronym, rather a statement of sentiment; https ://www.try-db.org; Kattge et al., 2011) was proposed with the explicit assignment to improve the availability and accessibility of plant trait data for ecology and earth system sciences. The Max Planck Institute for Biogeochemistry (MPI-BGC) offered to host the database and the different groups joined forces for this community-driven program. Two factors were key to the success of TRY: the support and trust of leaders in the field of functional plant ecology submitting large databases and the long-term funding by the Max Planck Society, the MPI-BGC and the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, which has enabled the continuous development of the TRY database.

Functional diversity is at the heart of current research in the field of conservation biology. Most of the indices that measure diversity depend on variables that have various statistical types (e.g. circular, fuzzy, ordinal) and that go through a matrix of distances among species. We show how to compute such distances from a generalization of Gower's distance, which is dedicated to the treatment of mixed data. We prove Gower's distance can be extended to include new types of data. The impact of this generalization is illustrated on a real data set containing 80 plant species and 13 various traits. Gower's distance allows an efficient treatment of missing data and the inclusion of variable weights. An evaluation of the real contribution of each variable to the mixed distance is proposed. We conclude that such a generalized index will be crucial for analyzing functional diversity at small and large scales.

Summary 1.We introduce a novel method that analyses environmental filtering of plant species in a geographic and phylogenetic context. By connecting species traits with phylogeny, traits with environment, and environment with geography, this comprehensive approach partitions the ecological and evolutionary processes that influence community assembly. 2. Our analysis extends RLQ ordination, which connects site attributes in matrix R (here environmental variables and spatial positions) with species attributes in matrix Q (here biological traits and phylogenetic positions), through the composition of sites in terms of species presences or abundances (matrix L). This methodology, which explores and identifies environmental filters that organize communities, was developed to answer four questions: which combinations of trait states are filtered by the environment, which lineages are affected by these filters, which environmental variables contribute to the assemblage of local communities and where do these filters act? 3. At La Mafragh in north-eastern Algeria, our approach shows that plant species traits were distributed according to environmental filters associated with a salinity gradient. Traits associated with the salinity gradient were convergent among Juncaceae, Cyperaceae and Amaranthaceae. The observed phylogenetic and trait patterns were related to how species survived the xeric season. Juncaceae and Cyperaceae, being perennials and anemogamous, tolerate the xeric hot season by restricting their range to the humid centre of the study area (where conditions are close to a subtropical climate). Several Amaranthaceae species co-occur with the Juncaceae and Cyperaceae in two areas with the highest salinity. Most dicots were observed at higher elevations (up to 7 m a.s.l.), had hairy structures that can retain water and reflect solar radiation and were mostly annual or biennial, completing their life cycle before the onset of the xeric season. 4. Synthesis. Our methodology describes environmental filters in terms of identified combinations of traits and environmental factors. It allows spatial and phylogenetic signals to be determined by identifying convergent and conserved patterns in the evolution of traits and spatial scales that structured the environment. Our statistical framework is generic and can be readily extended to a wide range of exciting issues, such as host-parasite, plant-pollinator and predatorprey interactions.