Biological and ecological investigations of islands are crucial to explain ecosystem functioning. Many studies on island biodiversity are carried out on oceanic islands. In contrast, information on continental islands, such as those in the Mediterranean Sea, is very often fragmented in space and time. Here, a synopsis of the Orchidaceae of Sardinia is presented based on literature surveys and recent botanical field studies. Our final list comprises of 64 species and 14 genera: thirteen species and subspecies were recognized as endemic and four new species were recorded for the flora of the island: Anacamptis palustris (Jacq.) R.M. Bateman, Pridgeon & M.W. Chase; Himantoglossum hircinum (L.) Spreng; Orchis italica Poir.; and Platanthera kuenkelei subsp. kuenkelei var. sardoa R.Lorenz, Akhalk., H.Baumann, Cortis, Cogoni & Scrugli. This orchid richness reflects the geological history of the island that was linked to the mainland several times, facing long periods of isolation. We also discuss a critical point-of-view of the biodiversity shortfalls still problematic for insular orchids. Indeed, within the Mediterranean Basin, the greatest amount of endemism occurs mainly on large islands, and, despite a long history of botanical exploration in European countries, many of them are scarcely investigated. This annotated synopsis shows the potential of continental islands to understand trends in ecology and evolution. Further studies are required to complete our knowledge of the orchid diversity on continental islands in order to propose scientific-based conservation programs to preserve these unique taxa.
Keywords: Mediterranean Basin; Orchidaceae; Sardinia; continental island; evolution; geographic isolation.