Ecology and phytosociology of endangered psammophytic species of the Omphalodes genus in western Europe

Abstract Omphalodes kuzinskyanae Willk. is an endangered annual plant of the family Boraginaceae, endemic to a narrow coastal area in the Lisbon region (Portugal). Omphalodes littoralis Lehm. occurs in northwest Spain (subsp. gallaecica) and northwest France (subsp. littoralis). Three approaches were used to assess the ecological requirements of O. kuzinskyanae: (1) physical and chemical characterization of their habitat soil; (2) phytosociological analysis; (3) comparison of several life history parameters under different light conditions. Germination experiments were conducted to evaluate seed dormancy. The results show that O. kuzinskyanae occurs in thin sandy soil with a substantial amount of organic matter and clay, mostly over limestone pavements. Phytosociological analysis shows that O. kuzinskyanae occurs both in sciophytic and heliophytic communities. Life history comparisons demonstrated that this plant has a strong preference for sciophytic conditions: under strong shade, plants have a higher survival rate, attain a greater height and width, and produce approximately nine times more seeds than in sunny conditions. In contrast with O. kuzinskyanae, published data on O. littoralis indicate that this species occurs in heliophytic conditions. This group of Omphalodes is possibly limited both in geographical distribution and habitat by its vulnerability to hydric stress. Scenarios are discussed that can explain the extensive gap separating the present ranges of the two species and their ecological differences. We propose two new syntaxa: Linario arenariae-Omphalodetum littoralis, Geranio purpurei-Galietum minutuli omphalodetosum kuzinskyanae.