Spiroplasmas (class Mollicutes, order Mycoplasmatales, family Spiroplasmataceae) are recognized today as a fascinating and rapidly expanding group of unique microbial agents. The beginning of spiroplasmal taxonomy can be traced, perhaps, to the cultivation of mycoplasmas (spiroplasmas) from citrus plants infected with stubborn disease in the early 1970s [1, 2]. These organisms were designated Spiroplasma citri by an international research team in 1973 [3]; the taxonomic description by this group and a supplementary study [4] outlined some of the basic morphological, nutritional, serologic, and molecular properties of spiroplasmas. These studies also confirmed the similarity of spiroplamas to other mycoplasmas assigned to the class Mollicutes and clearly differentiated the spiroplasmas from helical prokaryotes (spirochetes) that possess cell walls and periplasmic fibrils (axial filaments). It is now clear that S. citri is the type species of a genus that contains a wide array of related organisms. It seemed natural to expect that, as other spiroplasmas were grown on artificial medium and characterized, serologic properties would define a series of new species of Spiroplasma. Unfortunately, the corn stunt spiroplasma (CSS), the next organism in this group to yield to cultivation attempts [5, 6], posed some difficulties. Although CSS isolates were clearly distinct from strains of S. citri, they also shared a considerable number of antigens with S. citri [5-7]. This unexpected finding suggested the necessity for restraint in assigning taxonomic designations to CSS or to any other new spiroplasmas until more complete serologic analyses were performed and some information on genome properties became available. Voluntary restraint in the naming of new species of Spiroplasma on the basis of inadequate information was practiced, with few exceptions [8-10]. In retrospect, this restraint has been fully justified, for, in the six years since the CSS was first cultivated, at least 20 spiroplasmal isolates recovered