Strange? Neither an animal, nor a plant, nor a fungus— something entirely unique with astonishing capabilities. The slime mold Physarum polycephalum is the largest single-celled organism in the world. What you see in the images is the yellow plasmodium feeding on grains of rice. The rectangular piece of agar is the medium on which I acquired the slime mold in its dry dormant phase (sclerotium).

The life cycle of Physarum polycephalum consists of several phases. It initially begins in the spore phase, where the slime mold survives by forming spores that are dispersed in the environment. These spores are resilient and can endure for long periods under unfavorable conditions. When conditions are favorable, the spores germinate and develop into mobile amoebas known as myxamoebas. These myxamoebas are amoeboid and can actively move in search of food, such as bacteria and organic matter.

When multiple myxamoebas meet, they can fuse together to form a plasmodium. In this multinucleate phase, which is responsible for growth and feeding, the slime mold exhibits remarkable behaviors, efficiently navigating mazes and remembering pathways as well as negative experiences.

When environmental conditions become unfavorable, such as during food scarcity or drought, the plasmodium transforms into the fruiting body phase, in which it produces fruiting bodies that contain spores. It is important to note that the plasmodium also transforms into the fruiting body phase in response to light. These spores can then revert to the spore phase, completing the life cycle. Additionally, the slime mold can enter a dry dormant phase, during which it shifts into an inactive state and survives as a sclerotium until conditions become favorable again.

Moreover, Physarum polycephalum can split into multiple individuals and fuse with other individuals, merging memories as well. Not only does it serve as a model organism for science, but its capabilities also stimulate philosophical reflections on how to define intelligence.