Genetic structure of Spartina hybrids between native Spartina maritima and invasive Spartina densiflora in Southwest Europe

•Genetic structure of Spartina hybrids was determined by that of their parents.•Hybrids were genetically more similar to S. maritima than to S. densiflora.•Hybrids with greater genetic differentiation were more spatially separated from each other.•Hybrids with greater genetic differentiation were present in contrasted environments.•No correlation was found between the molecular markers and plant traits.