 It is an extracellular parasite.All stages are found in lungs and because they cannot be cultured "ex vivo", direct observation of living "Pneumocystis" is difficult.The trophozoite stage is thought to be equivalent to the so-called vegetative state of other species (such as "Schizosaccharomyces pombe") which, like "Pneumocystis", belong to the Taphrinomycotina branch of the fungal kingdom.