Abstract. Devillers, P. & Devillers-Terschuren, J. - Biogeoraphical transitions in some Euophrys populations of the northeastern Tyrrhenian [Natural. belges 81 (Orchid. 13) (2000): 339-352 + 4 figs]. The distribution of orchids of genus Ophrys is particularly complex in the Italian peninsula. Western Mediterranean taxa come in contact with Iono-Aegean, southern Mediterranean or medio-European elements. It is thus not surprising that numerous questions of congruence between phylogenesis and biogeography remain unanswered, even in coastal regions where the linearity of distributions makes the interpretation of distributions simpler. The note addresses some of these problems within the group of Ophrys arachnitiformis, that of O. argolica and their domain of interaction. It is suggested that the core arachnitiformis chain of species, which displays a peri-Tyrrhenian distribution anchored on O. arachnitiformis of southern France and O. exaltata of southern Italy, is represented along the Tyrrhenian coasts of Italy by green-sepals forms that have long been confused with O. sphegodes, one of which, O. classica, is described as new. Further, a second chain of forms is outlined, comprising the Iono-Adriatic taxa O. cephalonica, O. archipelagi, O. mateolana, the Tyrrhenian species O. tyrrhena, and the newly discovered and described O. cilentana. It is argued that this chain may constitute a primitive lineage within the O. sphegodes constellation, morphologically close to a common root with the O. argolica group. Its distribution in Italy closely parallels that of the O. argolica group, O. archipelagi being sympatric with O. biscutella, O. tyrrhena with O. crabronifera and O. cilentana with O. pollinensis, which is recognised as a species distinct from both O. biscutella and O. crabronifera.

Key-words: Orchidaceae, genus Ophrys, Ophrys arachnitiformis, Ophrys classica, Ophrys argentaria, Ophrys exaltata, Ophrys praecox, Ophrys tyrrhena, Ophrys cilentana, Ophrys cephalonica, Ophrys archipelagi, Ophrys mateolana, Ophrys pollinensis, Ophrys biscutella, Ophrys crabronifera, France, Italy, Liguria, Monte Argentario, Cilento, biogeography.