Many variants of "T. grandiflorum" have green markings on the petals, as well as anywhere from 4 to 30 extra petals or bracts along with other highly deformed characteristics. Although many of these forms have been given taxonomic names, it has been shown that mycoplasma-like organisms called phytoplasma are responsible for the altered morphology in these individuals and not genetic variation. "T. grandiflorum" does, however, occasionally produce double-flowered forms such as "T. g." f. "polymerum" but these are almost invariably sterile. It is the species of trillium that produces double flowers most frequently. On the other hand, and unlike other species such as "T. erectum", which hybridize fairly easily, "T. grandiflorum" is not known to form hybrids.