pleomorph

A pleomorph is an organism or cell that can assume multiple distinct shapes or forms. The term derives from Greek pleion, more, and morphe, form. In biology and medicine, pleomorphism describes variability in morphology within a group, species, or developmental stage.

In microbiology, pleomorphism refers to bacteria and other microbes that do not maintain a single fixed shape. Some species show a range of shapes under different conditions. Classical examples include wall-deficient organisms such as Mycoplasma, which may appear coccoid, filamentous, or irregular; shape can change with growth phase and environment. Not all observed variation reflects a defined biology; some forms may be artifacts of culture or specimen handling.

In pathology, pleomorphism is used to describe variability in cell size and shape within a tissue. A high degree of pleomorphism, seen in many malignant tumors, reflects cellular atypia and genomic instability and can influence diagnosis and grading.

The concept originated in early microscopy and has since become a general descriptor for intentional or incidental variation in cell morphology. In modern biology, pleomorphism is recognized as a real biological property in some organisms, while in others it may simply reflect environmental stress or technical conditions.

See also: pleomorphism; Mycoplasma; bacterial morphology.