SUMMARYCronartium fusiformeis considered conspecific withC. quercuumbased on morphological studies, but maintained as a distinctforma specialisofC. quercuumbecause of its restricted host range onPinus taedaandP. elliottii.Three other special forms ofC. quercuumare proposed for physiological entities that selectively attackP. banksiana, P. echinata, orP. Virginiana.The importance of recognizing the conspecificity and genetic plasticity of these organisms when breeding resistant pines is emphasized.