Classifying slime mold species

Identifying slime molds is just as tricky as defining what a slime mold is. Often you cannot be a hundred percent sure with your classification, especially if you are only holding a picture in your hand. I myself would not count myself as an expert in this area, more as an "advanced layman". But for the general classification of slime mold species I collected some tools and strategies which I'd like to share with you here. To encourage you: Some species show obvious features!

What are typical markers for identification and classification?

That depends on what's in front of you:

• a simple photo
• a real, living slime mold

We have to differ here, because a photo usually only shows a single stadium of the life cycle of a slime mold. If you have a living slime mold or spore mass, you can of course start various analysis and experiments to really get to know your slimy friend.
Now, for the next step of classification we should identify the exact stage of the life cycle the slime mold is in:

• Plasmodia
• Beginning fructification with formation of fruiting bodies
• Sclerotium
• Fructification with intact fruiting bodies (still carrying the spore mass)
• "Empty" fructification (spores are gone, more or less)

I won't focus on the stages of "myxamoebae", "myxoflagellate" and "spores", since it is highly unlikely to find single cells like that. Also, it is truly impossible for a laymen to classify these correctly!
In the following, I concentrate on a simple visual identification, so without decomposing and microscopic evaluation. This means you can also use this guideline if you only have a single photo.

Next, we're having a look at different properties that make out for the distinct stadium:

• Colors (be precise!)
• Shape
• Size (sometimes hard to tell on a photo)
• Condition (any damage to the slime mold?)
• Surface properties (texture): smooth, rough, porous, slimy, powdery, fibrious, ...
• Number and arrangement (especially for fruiting bodies)
• Substrate

For more details you can have a look at some of the features I described on the pages about the different stages of the life cycle.

But first let's see how the taxonomy of slime mold species looks like (source: wikipedia.de/Schleimpilze). All links lead to the galleries showing the particular species in case I have some photos.

Identification of plasmodia

For identification of plasmodia, the color and shape play a major role. The simplest way for classification is by comparing with pictures of specific species (you can start with the links to the gallery in the table above). I collected some typical identifications that could help you in most cases:

• Yellow plasmodium: Family of Physaridae. In case of a spongy structure, Fuligo septica is very likely. If you can make out veiny structures or even some "leading edges" for movement, Badhamia utricularis could be your new best friend or a species of the genus Physarum. They are all pretty common in this neck of the woods. But do not forget Metatrichia vesparia or Arcyria (very widespread species!).
• White plasmodium, spongy: Are there any yellow borders? Then it is probably Fuligo septica (they often turn white shortly before forming a fruiting body)
• White plasmodium and not Fuligo septica: That's a tricky one. Possibly a slime mold of the Didymiidae family, but Trichia might also be likely as well as many other species...
• Red plasmodium: Either you have a "wolf's milk" (Lycogala epidendrum, very common, forms round, pink fruiting bodies with a rough, "peeling" surface) or Metatrichia
• Very obvious species that are easy to identify are Ceratiomyxa fructiculosa, Stemonitis and Hemitrichia serpula

With sclerotia, the identification is very similar. However, this classification guide is just a rough estimate with the correct identification of plasmodia being nearly impossible.

Identifying fruiting bodies (macroscopic)

This is a lot easier! Here we are considering the following features:

• Colors
• Size
• With stem / sitting directly on the substrate
• Spherical / elongated / bent fruiting bodies
• How close are the fruiting bodies sitting next to each other?
• In case the fruiting bodies are empty and the spore mass is gone: Can you see any internal structures such as meshes or fibers?
• In case you can see the spores: Which color are they? (If you have access to a microscope: use it! And have a closer look at the surfaces, colors, sizes....)

An easy way is to compare your findings with other photos on the internet that have already been classified. A tip: eye-catching and unique shapes can be found for Stemonitis, Ceratiomyxa, Arcyria, Physarum polycephalum, Badhamia utricularis, Metatrichia vesparia and Hemitirichia calcylata, for instance. Sometimes we have to consider ourselves satisfied if we can narrow the possible identifications to one or two slime mold families or genus (noted, e.g. like Physarum sp.).

For image comparison

A really helpful site can be found here www.discoverlife.org. It is updated regularly and the database is immense, sorted according to the species.

In case you have a guess which type of slime mold you have, I highly recommend to use a search engine with the species' name. Do the search results match your own slime mold? A more precise search will return more fitting results than the simple search text "slime molds".

Otherwise, if you do not have any idea about your slime mold, try to google using more general terms such as "slime molds", "Myxomycetes", "Eumycetozoa", "Schleimpilz" or "Myxogastria" and set color filters.