a classification scheme for mycobacteria other than Mycobacterium tuberculosis that divides species into four categories: photochromogens, species that produce a yellow to brown carotene pigment when grown in the presence of light; scotochromogens, which produce pigment in presence or absence of light; nonpigmented, which do not produce pigment; and rapid growers, which grow on solid media in 5-10 days rather than 4-8 weeks. This classification has no clinical or genetic significance but does remain of limited value in identification of some clinical isolates.