| Record | Value | Context |
|---|---|---|
| Mating types | 720 | Produced by combining three genes, matA, matB and matC. One of the most complex compatibility systems among eukaryotes |
| Top speed | 4 cm/h | At the leading edge, in ideal conditions (22 to 25 °C, food nearby, steady humidity). Closer to 1 cm/h in a dish at home |
| Maximum size | No known limit | It keeps growing as long as it is fed. No size record has been measured and published in a verifiable way |
| Survival as a sclerotium | 2 years and more | Sclerotia stored dry and in the dark routinely revive after two years |
| Nuclei in one cell | Billions | In a large plasmodium, all sharing the same cytoplasm |
| Doubling time | About 1 day | In ideal conditions with plenty of food |
| Ideal temperature | 22 to 25 °C | It slows down sharply below 15 °C and suffers above about 30 °C |
| Cytoplasm pulse | About 100 seconds | One back-and-forth cycle of the flow that runs through its veins |
| Maze solved in | About 8 hours | Nakagaki's experiment (Nature, 2000): four possible routes between two food sources, the shortest one kept |
720 mating types from three genes
Most animals have two sexes, decided by sex chromosomes. Slime mold works on a completely different principle, and it is probably its most surprising record.
Three genes decide whether two reproductive cells can pair up. The matA gene comes in 16 known versions (alleles), matB in 15 and matC in 3. Every cell carries one version of each, which gives 16 × 15 × 3 = 720 combinations, and so 720 mating types. Two cells can only pair if their combinations differ, so any slime mold is compatible with almost every partner it meets.
It is not the absolute record. The split-gill fungus Schizophyllum commune has more than 20,000 mating types. But 720 is still a world away from the two-sex system of most animals.
How big can a slime mold get?
In principle there is no maximum size. A plasmodium keeps growing as long as it finds food and conditions stay right. In practice three things hold it back: food running short at the far ends of a large network, a substrate drying out, and predators such as slugs and beetles that graze on it.
No size record has been measured and published in a way anyone can check. Figures of several square meters circulate online, always without a source. What is known is that a well-fed slime mold roughly doubles its area every day, and that in the wild a plasmodium a few tens of centimeters across is already a good find.
Is 4 cm an hour slow or fast?
At human scale, 4 cm an hour sounds like nothing, barely a meter a day. But a slime mold does not drag a compact body along like a snail. Its whole mass flows forward through a network that can span tens of centimeters. In a 9 cm Petri dish, a healthy slime mold crosses from one side to the other overnight, which is plenty to see progress from one day to the next.
The 4 cm/h figure is a peak measured in the lab on smooth agar. At home, expect something closer to 1 cm an hour. Inside the veins the cytoplasm moves much faster, at up to about a millimeter per second, sloshing back and forth roughly every 100 seconds. That pulsing flow is what drives the whole organism, as explained on our page about how slime mold moves.
Billions of nuclei in a single cell
A large plasmodium contains an almost unimaginable number of nuclei. A slime mold a few centimeters across already holds millions, and the largest hold billions. None of them is walled off from the others. They all float in the same cytoplasm, and when the slime mold is cut in two, they spread between the pieces so that each piece can live on as a complete organism.
Two opposite strategies
The human body is made of about 37 trillion separate cells, each with its own job. A large slime mold packs billions of nuclei into a single cell with no internal walls. One bets on division of labor, the other on a shared cytoplasm with no borders.
Dormancy, the real record and the most misquoted
A properly formed sclerotium, stored dry and away from light, revives without trouble after several years. Revivals after more than two years are common, including in home cultures.
Beyond that, be careful. You will often read about sclerotia or spores revived after decades. Those claims are anecdotal and rarely backed by a protocol anyone could repeat. What limits survival is less the passing of time than the quality of the initial drying and how stable the storage stays. A badly dried sclerotium will not make it through a single winter. The method is explained in our guide to reviving a sclerotium.
Three records that are not records
Several feats credited to slime mold do not survive a closer look.
"It doubles in size every hour." False. The front advances a few centimeters an hour, which is not the same as doubling its mass. Doubling takes about a day in good conditions.
"It is the fastest organism without muscles." Impossible to check, and probably false. Many ciliates move far faster for their size. What sets slime mold apart is the sheer mass it moves, not its speed.
"It is the largest single-celled organism in the world." Disputed. Some algae of the genus Caulerpa, which are also giant cells with many nuclei, spread over several meters. Slime mold is among the largest, which is remarkable enough.
What all these records have in common
Every one of these feats depends on the same three conditions: a temperature around 22 to 25 °C, steady humidity and darkness. Step outside that window and the numbers collapse, whatever the strain. That is the subject of our page on the ideal environment, and it is also why lab records are rarely matched at home.
Frequently asked questions
What is the largest slime mold ever recorded?
No reliable measurement has been published. In the wild, a plasmodium a few tens of centimeters across is already large. In the lab, its size is limited by the container and the food it gets, not by the organism itself.
How long can a slime mold stay dormant?
Several years, reliably, if the sclerotium was dried properly and kept dry and in the dark. Claims of several decades are not seriously documented.
Is slime mold immortal?
No. It has no programmed aging, which is a different thing. It dies from sudden drying, contamination, heat or prolonged starvation.
Can slime mold really move 4 cm an hour?
Yes, but that is a peak reached on smooth agar at the ideal temperature. In a home culture on ordinary substrate, expect around 1 cm an hour.
Sources
- Nakagaki T., Yamada H., Tóth Á., Maze-solving by an amoeboid organism, Nature 407, 470 (2000).
- Tero A. et al., Rules for biologically inspired adaptive network design, Science 327, 439-442 (2010).
- Physarum polycephalum, French Wikipedia, for the three mating-type genes.