Physarum polycephalum, an acellular[1] slime mold or myxomycete popularly known as "the blob",[2] is a protist with diverse cellular forms and broad geographic distribution.

The “acellular” moniker derives from the plasmodial stage of the life cycle: the plasmodium is a bright yellow macroscopic multinucleate coenocyte shaped in a network of interlaced tubes.

This stage of the life cycle, along with its preference for damp shady habitats, likely contributed to the original mischaracterization of the organism as a fungus.

In the laboratory, amoebae are grown on lawns of live or dead Escherichia coli on nutrient agar plates, where they can multiply indefinitely.

[4] The plasmodium is typically diploid and propagates via growth and nuclear division without cytokinesis, resulting in the macroscopic multinucleate syncytium; in other words, a large single cell with multiple nuclei.

Like amoebae, the plasmodium can consume whole microbes, but also readily grows axenically in liquid cultures, nutrient agar plates and on nutrient-moistened surfaces.

When exposed to light, the starving plasmodium differentiates irreversibly into sporangia that are distinguished from other Physarum species by their multiple heads (hence polycephalum).

The life cycle is completed when haploid amoebae of different mating types fuse to form a diploid zygote that then develops by growth and nuclear division in the absence of cytokinesis into the multinucleate plasmodium.

[11] For dumbbell-shaped microplasmodia, often termed Amoeboid plasmodia, stiffening of the cortex in the rear versus the front seems instrumental in breaking the symmetry for the contraction wave to translate into migration.

[14] It is likely that the feedback of transported signals on tube size underlies Physarum's capability to find the shortest path through a maze.

Similar results have been shown based on road networks in the United Kingdom[19] and the Iberian Peninsula (i.e., Spain and Portugal).

[23][24] In one particular instance, a specimen placed at the center of a Petri dish spatially re-allocated over combinations of food sources that each had different protein-carbohydrate ratios.

For each specimen, the results were consistent with the hypothesis that the amoeba would balance total protein and carbohydrate intake to reach particular levels that were invariant to the actual ratios presented to the slime mold.

[27] In a book[28] and several preprints that have not been peer-reviewed,[29][30] it has been claimed that because plasmodia appear to react in a consistent way to stimuli, they are the "ideal substrate for future and emerging bio-computing devices".

[30] An outline has been presented showing how it may be possible to precisely point, steer and cleave plasmodium using light and food sources,[30] especially Valerian root.

When the primitive logic gates are connected to form more complex functions, the plasmodium ceased to produce results consistent with the expected truth tables.

Even though complex computations using Physarum as a substrate are currently not possible, researchers have successfully used the organism's reaction to its environment in a USB sensor[32] and to control a robot.

Both Nicotiana tabacum and the beans Phaseolus vulgaris and Vigna sinensis suffered almost no lesioning in vitro from TMV or TRSV when treated with a P. polycephalum extract.