polycephalum

Physarum polycephalum is a species of plasmodial slime mold in the family Physaraceae. It is widely used as a model organism in biology and unconventional computation because of its simple cellular organization and complex emergent behavior. In culture, it forms bright yellow to orange plasmodia that can span several centimeters.

The organism at the plasmodial stage consists of a single, multinucleate mass of cytoplasm, the plasmodium, that moves by rhythmic cytoplasmic streaming. The plasmodium crawls along surfaces through coordinated contractions and internal flow within a network of tubular veins. It feeds by engulfing bacteria and nutrients on its substrate, expanding its network where resources are plentiful and retracting where they are scarce. When conditions become unfavorable, the plasmodium differentiates to form fruiting bodies (sporangia) that produce spores for dispersal, enabling survival and propagation. Sexual reproduction can occur under certain stress conditions, though asexual growth is common in laboratory cultures.

Natural habitats include decaying leaves, wood, and moist soils in forests and gardens. In the laboratory, P. polycephalum is commonly cultured on non-nutrient agar with oat flakes, producing large, easily observed plasmodia. It tolerates a range of temperatures but requires moisture and a food source to maintain growth.

Research significance lies in studies of chemotaxis, motility, and signal transduction in a simple eukaryotic model. Notably, Physarum has demonstrated foraging behavior that can approximate efficient network designs; experiments have shown its ability to solve mazes and adapt networks in response to changing environments. These properties have made it a focal point in discussions of distributed computation, optimization, and emergent behavior.