Abstract. Delforge, P.- Contribution to the knowledge of the Ophrys tenthredinifera species group in the eastern Mediterranean basin [Natural. belges 86 (Orchid. 18) (2005): 95-140]. Till now, the Ophrys tenthredinifera species group seemed to be represented in the eastern Mediterranean basin only by one polytypical species, O. villosa Desfontaines 1807, or by two subspecies of O. tenthredinifera Willdenow 1805 the subspecies tenthredinifera, regarded as a large- and late-flowered taxon, and O. tenthredinifera subsp. villosa, regarded as a small- and early-flowered  one. A review of morphological and phenological variations of Ophrys villosa s.l. within its eastern mediterranean range shows that O. tenthredinifera s. str. is not present in the area and that at least four entities are identifiable in the Aegean and Ionian basins, well defined by flower size, phenology, as well as characteristics of the labellum and the stigmatic cavity. Three of them flower successively in Crete. The earlier possesses medium-sized flowers and flowers from January till early in March; it is newly described here as Ophrys dictynnae. The second is small-flowered and flowers in March; it occurs at least in the eastern part of the Aegean basin and is identifiable to Ophrys villosa s. str. The third is large-flowered and flowers from the end of March till early in May; it possesses a large distribution and occurs notably in the Ionian islands, the northern continental marges of the Corinthian Gulf, the Attica, the Euboea, the Peloponnese, the Cyclades and the Dodecanese; it is newly described here as Ophrys leochroma. Besides the latter, a small-flowered taxon occurs in the Ionian islands; it flowers in April and is newly described here as Ophrys ulyssea. A list of 230 localities attributable  to the four species, based on prospections in Greece since 1974, is provided.

Key-Words: Orchidaceae; genus Ophrys, Ophrys tenthredinifera species group, Ophrys villosa, Ophrys dictynnae sp. nova, Ophrys leochroma sp. nova, Ophrys ulyssea sp. nova; flora of Greece.