They are obligate parasites of plant phloem tissue. Their vectors are insects which inject then into the plant cells. They were discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be grown in vitro (in laboratory conditions), and that limits the information about them. They are described by the special term "Candidatus", reserved for such difficult organisms.
↑Marcone C, Gibb KS, Streten C, Schneider B (2004). "'Candidatus Phytoplasma spartii','Candidatus Phytoplasma rhamni' and 'Candidatus Phytoplasma allocasuarinae', respectively associated with spartium witches'-broom, buckthorn witches'-broom and allocasuarina yellows diseases". International Journal of Systematic and Evolutionary Microbiology54 (4): 1025–1029. doi:10.1099/ijs.0.02838-0. PMID15280265.
↑'Obligate' means they cannot live except as parasites.
↑Doi, Y; Teranaka M, Yora, K and Asuyama, H (1967). "Mycoplasma or PLT-group-like organisms found in the phloem elements of plants infected with mulberry dwarf, potato witches' broom, aster yellows or paulownia witches' broom". Annals of the Phytopathological Society of Japan33 (4): 259–266. doi:10.3186/jjphytopath.33.259.