Distribution of orchid records and species richness across Madagascar, using fixed grid cell sizes of 1° x 1° (a-d) and 0.5° x 0.5° (e-h); a and e, number of herbarium records (samples) collected per grid-cells; b and f, number of species collected per grid-cells; c and g, unbiased estimate of species diversity per grid cell, Hurlbert’s effective number of species (Ek) found in grid-cells that contain at least 10 herbarium records (Ek = 10); d and h, unbiased estimate of species diversity per grid cell, Hurlbert’s effective number of species (Ek) found in grid-cells that contain at least 100 herbarium records (Ek = 100).