polymyxa graminis polymyxa graminis polymyxa graminis is a species of plasmodiophorid cercozoans. it is an obligate parasite of plant roots and, though itself non-pathogenic, is responsible for the transmission of several very important plant viruses, including barley yellow mosaic virus (baymv) and soil-borne wheat mosaic virus (sbwmv). polymyxa graminis scientific classification (unranked): sar (unranked): rhizaria phylum: cercozoa class: plasmodiophorea order: plasmodiophorida family: plasmodiophoridae genus: polymyxa species: p. graminis binomial name polymyxa graminis