What You Should Know
Leocarpus fragilis is not actually a fungus. It is a slime mold. Slime molds were historically classified as fungi, but today they belong to the class of true slime molds, Myxomycetes.
This slime mold is found worldwide and typically inhabits shady, cool, moist areas, growing on decaying leaves and logs.
Fruiting bodies are very small, 2 mm in diameter. They are ovoid-shaped and their color ranges from vivid yellow to reddish-brown. The surface is very smooth and shiny. It is typically yellow and eats fungal spores, bacteria, and other microbes. It is not a fungus. It is easy to confound with Fuligo septica, with yellow color, but without visible fruiting bodies.
It’s important to realize that slime molds are very sensitive to environmental conditions. The best time to observe the plasmodial phase is immediately following a period of rain. The shift from the plasmodial phase to the spore-forming phase is rapid, literally occurring overnight.
Leocarpus fragilis Life Cycle
The main vegetative phase of this organism consists of the plasmodium (the active, mobile, streaming phase), a membrane-bound, giant single cell, containing multiple nuclei. It is during this stage that the organism searches for food, creeping across decaying matter, spreading at an impressive rate, up to an inch per hour! The plasmodium surrounds its food and secretes enzymes to digest it.
The plasmodium generates networks of protoplasmic ‘veins’ that act as tunnels for nutrient transport. In this phase Leocarpus fragilis is very easy to see, and from a distance almost looks like egg yolk spilled on decaying logs and leaves.
When the plasmodium exhausts the available nutrients in the presence of visible light, it differentiates into specialized fruiting bodies, called sporangia, where spores are formed. These fruiting bodies eventually rupture, releasing the spores into the environment.
In this phase, Leocarpus fragilis may be mistaken for clusters of insect eggs, and this species of slime mold is commonly referred to as the ‘Insect-Egg Slime Mold’.
The shift from the plasmodial phase to spore forming phase is rapid, literally occurring overnight.
When the fruiting bodies first appear, they are bright orange and impossible to miss, but this stage is short-lived. Within 24 hours, they age and take on the same dull brown color of the decaying leaves and logs, and can be difficult to spot.
Slime molds are not plant parasites, they can injure young or small plants by smothering and shading them.
Photo 1 - Author: Ryan Durand (Creative Commons Attribution 4.0 International)
Photo 2 - Author: Joshua Morris (Public Domain)
Photo 3 - Author: P Holroyd (Creative Commons Attribution 4.0 International)
Photo 4 - Author: Peta McDonald (Public Domain)
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