Over the past century in California, the invasive weed Salsola tragus (russianthistle) has become a widespread and troublesome pest plant. Early attempts at biological control of russianthistle achieved only partial success. Efforts to improve effectiveness of renewed biocontrol efforts revealed that two distinct, often sympatric, genetic entities comprise what has been called Salsola tragus: Salsola tragus and Salsola ‘type B’. Efforts to identify and characterize ‘type B’ resulted in recognition of a third form, ‘type C’. We present a taxonomic and morphological examination of Salsola tragus, Salsola ‘type B’, Salsola ‘type C’ and Salsola paulsenii using discriminant analysis with DNA sequence genotypes as the taxonomic framework. Salsola tragus and ‘type B’ were morphologically distinct; ‘type C’ was morphologically intermediate between them and contained DNA sequence genotypes that were an additive mixture of haplotypes mostly exclusive to tetraploid S. tragus and others exclusive to diploid ‘type B’. ‘Type C’ is a fertile allohexaploid that originated via hybridization between S. tragus and ‘type B’. We provide a pre-existing name, Salsola australis, for ‘type B’, and propose Salsola ryanii sp. nov. for ‘type C’. Morphological variation, habitats, and dispersal behaviors among these Salsola taxa were examined in the herbarium and in the field. These are compared and discussed.