rods. History The first species of rhizobia, R. leguminosarum, was identified in 1889, and all further species were initially placed in the Rhizobium genus. However, more advanced methods of analysis have revised this classification, and now there are many in other genera. Most research has been done on crop and forage legumes such as clover, alfalfa, beans, and soy. However, recently more work is occurring on North American legumes. The word rhizobia comes from the Ancient Greek, "rhíz… (More on Rhizobia)