Estimated Time: 10–15 minutes
Course: Myxomycetes 101 — Introduction to Slime Molds
Lesson Type: Reading + Media (self-paced)

1. The Ever-Changing Life of a Slime Mold

Myxomycetes live a life of transformation — shifting between single cells and multinucleate masses, between motion and stillness, between feeding and fruiting.
Their entire cycle is a dance with the environment, responding to humidity, light, and temperature.

Stemonitis sp. — The life of a slime mold can be microscopic or visible to the naked eye, depending on its stage.

Learning Goals
By the end of this lesson, you’ll understand:

• The four key stages of the myxomycete life cycle.

• How environmental cues influence development and reproduction.

• Why each stage is crucial for survival and dispersal.

2. Step 1: Spore Germination

The journey begins with a spore, released from a mature fruiting body.
When conditions are moist and favorable, the spore germinates — splitting open to release an amoeboid cell (called a myxamoeba) or sometimes a flagellated swarm cell, depending on the species and environment.

Key Facts

• Spores are typically 5–15 µm in diameter.

• Germination requires free water or high humidity.

• The emerging cell immediately begins feeding on bacteria, yeasts, algae, fungi, and organic matter.

3. Step 2: Amoeboid Stage

Once free, each myxamoeba lives independently — crawling and feeding like a tiny amoeba.
When conditions dry out, it can encyst into a microcyst, waiting until moisture returns.

But under the right conditions — usually abundant food and moisture — individual cells fuse to form one of nature’s strangest life forms: the plasmodium.

At this stage:

• Feeds on bacteria and small particles.

• Moves by cytoplasmic streaming.

• May persist for hours or days before fusing.

Macro shot of a plasmodium beginning to form along side an Oligonema sp.

4. Step 3: Plasmodium — The Living Network

The plasmodium is the heart of the slime mold life cycle — a single, multinucleate mass of cytoplasm that can flow, crawl, and make “decisions”, chemical signals that are left behind that indicate whether a path will lead to food or not.
It moves toward food and away from light, leaving behind shimmering trails.

Fun Fact:
The plasmodium can learn — experiments show that Physarum polycephalum can remember patterns and solve mazes.

Inside the Plasmodium:

• Millions of nuclei share one membrane.

• Movement is rhythmic, driven by streaming of cytoplasm.

• It can reach several centimeters across.

“Plasmodia move slowly—about 1 cm/hour—but can navigate complex environments.”

5. Step 4: Sporulation — Building the Fruiting Body

When the environment becomes too dry, too bright, or food runs out, the plasmodium shifts from growth to reproduction.
It migrates to a drier, exposed surface and begins sporulation — forming tiny, intricate fruiting bodies that produce new spores.

Environmental Triggers:

• Humidity: High levels favor plasmodial activity; low humidity triggers sporulation.

• Light: Often initiates fruiting in combination with desiccation.

• Temperature: Most species fruit between 15–25°C (59–77°F).

Key Points:

• Each sporangium can produce thousands of spores.

• The peridium (outer wall) protects spores until conditions favor dispersal.

• Spores spread by air currents, rain splash, or animals — beginning the cycle again.

6. Recap: The Myxomycete Life Cycle

The full cycle, simplified:

Spore → Myxamoeba (or Swarm Cell)
→ Fusion → Plasmodium
→ Sporulation → Sporangium → Spore

Adaptations at Each Stage:

• Survival in harsh conditions (spores, cysts).

• Rapid growth and feeding (plasmodium).

• Efficient dispersal and genetic recombination (sporulation).

• Dormant hibernation (Sclerotium), which can be awoken

Life cycle of a Myxomycete