Although technically this should be our ‘Mushroom Monday’ post, Leocarpus fragilis is not actually a fungus.  However, while out hunting for mushrooms, it really caught my eye, and thought it worth a mention.

Leocarpus fragilis on Redwood leaf litter

Leocarpus fragilis is a slime mold.  Slime molds were historically classified as fungi, but today they belong to the class of true slime molds, Myxomycetes.  As soon as the clouds parted after last week’s heavy rain, this slime mold seemed to be everywhere.

Leocarpus fragilis on decaying maple leaves

Leocarpus fragilis is found worldwide, and typically inhabits shady, cool, moist areas, growing on decaying leaves and logs.

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.

Plasmodial phase of Leocarpus fragilis

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.

Plasmodial phase of Leocarpus fragilis on an oak twig

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.

The early fruiting bodies of Leocarpus fragilis resemble clusters of insect eggs

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’.

It’s important to realize that slime molds grow and regress quickly, and are very sensitive to environmental conditions. The best time to observe the slime-like plasmodial phase is immediately following a period of rain. The shift from the plasmodial phase to spore forming phase is rapid, literally occurring overnight.

The plasmodial phase of many slime molds is short-lived

The same Madrone log as the previous image, less than 48 hours later. The slime mold has completely transformed from plasmodium to spore producing fruiting bodies.

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.

Newly emerging fruiting bodies of Leocarpus fragilis

Within 24 hours the color of the fruiting bodies has faded from bright orange, to brown

Unlike some of the fungi we’ve seen, slime molds do not seem particularly fussy about substrate.  Within just a few feet, I found it growing on the decaying leaves of California Big Leaf Maple, Redwood, and Oak, and even amidst the moss on the north side of an old standing Live Oak.

Leocarpus fragilis on the north side of an oak, with moss, and Mycena sp. mushroom

Occasionally slime molds may appear on living plants in the garden.  Although they are not plant parasites, they can injure young or small plants by smothering and shading them.  A strong jet of water from a hose is usually sufficient to dislodge them.  Left alone, slime molds will disappear once atmospheric conditions no longer favor their growth.

I’ll leave you with an interesting short video from YouTube. The first 30 seconds of this video shows the growth of a similar slime mold using time lapse photography.

If embedded video does not display, click here to view