Not All Fungi-eating Slime Molds are Physarum polycephalum: Badhamia utricularis

Badhamia utricularis plasmodium engulfing Pleurotus populinus.

I found my first fungicolous myxomycete (a slime mold living on a fungus) two years ago in the height of the Pleurotus populinus (spring oyster) season. If I hadn’t been deep in the woods, I would probably have been able to see it from a kilometer away, it was such an unearthly bright yellow-orange. Up close, it was clearly an extensive slime mold plasmodium that was attempting to engulf two separate clusters of oyster mushrooms that were well past their frying-pan expiry date.

Badhamia utricularis plasmodium Day 1 (top) & Day 2 (bottom)

I could have left this spectacle where it was, but I’d been wanting a new pet, so I took the whole kit and caboodle home with me. I say “pet” because I’d read quite a bit about the plasmodium of a particular slime mold—Physarum polycephalum—and had been keeping my eyes peeled, hoping to find some that I could capture and tempt into solving mazes or planning efficient rail systems by baiting it with oatmeal as other people had been doing. It sounded like fun. Cheap fun.

The yellow plasmodium travelled on an off the mushrooms for several days.

First, though, I was curious about whether or not the plasmodium I’d found was actually consuming the oyster mushrooms I’d found it on, or if it was simply passing over them. I took photographs over several days and watched my myxo completely cover the Pleurotus, then move off into a corner for a few hours (perhaps to relax and digest?), then return to the quickly shrinking mushrooms and engulf them again. It repeated this pattern for four days, and during this time the mushrooms shrank and shrank and shrank. Unusually, there were no signs of the normal larvae that one finds gorging on the tender flesh of the most edible Pleurotus species, the bane of fungi-eating people everywhere, and I believe this was solely due to the active presence of the plasmodium, which had either deterred the inevitable laying of eggs by insects or had somehow made eggs that had been laid unviable.

Plasmodium Day 4 (top) and Day 5 (bottom)

An interesting thing about Physarum polycephalum, which is studied in labs around the world, is that there are very few pictures of mature sporangia—the structures that produce spores—on the internet. There are even fewer examples of a progression from plasmodium to sporangia. Despite this lack of sporangial evidence, there are many photographs of yellow plasmodium on line that look just like mine, and a great many of these are labeled as Physarum polycephalum. Some are engulfing mushrooms. Some of these mushrooms are species of Pleurotus. Furthermore, in a 1987 paper, Quentin D. Wheeler states that Pleurotus is “so often the substrate over which this slime mold grows that the plasmodium is a field identification “character” of the fungus itself (Lincoff 1981*).” Obviously, I had found my first Physarum polycephalum. Or had I?

The sporangia beginning to form.

From early on, I was a tad disturbed by the colour of my new “pet,” which seemed a little off, a little too orange-yellow compared to the yellow to greenish-yellow it was supposed to be if it was really Physarum polycephalum. 

Sporangia beginning to get their mature blueish grey colour.

And then my plasmodium crawled away from the flattened, liquefied remnants of the mushrooms it had been consuming and formed sporangia that were not at all what they were supposed to be. In fact, what they turned into was a big whack of Badhamia utricularis.

Badhamia utricularis sporangia are brownish
before drying to blue-grey.

Surprisingly, this was not an anomaly. I found another batch of mature B. utricularis in the winter that had apparently been feeding on a Trametes before it, too, had formed sporangia. And then, again, this past spring, I found new clusters of Pleurotus populinus being eaten by, once again, B. utricularis at two different sites.

B. utricularis sporangia are usually pendant, hanging
in clusters by shrivelled yellowish strands.

So I did a little more detective work and found a most entertaining 1906 article written by a past president of the British Mycological Society, Arthur Lister: “Notes on the Plasmodium of Badhamia utricularis and Brefeldia maxima.”

Arthur Lister, who kept slime moulds as pets.

Arthur Lister made his money as a wine merchant, then retired so he could devote his time and energies to the study of botany, primarily myxomycology, which allowed him time to observe and write notes about a pet B. utricularis that he “kept in constant streaming movement on various types of woody fungi for more than a year.” (Sometimes I wish I’d been a born in the 1800s. Male. To a family of means.) (Oh, yeah—with a daughter, Gulielma, who would do all the gorgeous, detailed illustrations for my book: A Monograph of the Mycetozoa (1894.))

Gulielma Lister and her amazing illustration of Trichia affinis. 

Lister found his Badhamia on a garden log where it was consuming portions of an extensive patch of Coniophora puteana. He captured some of it and kept it alive in specially constructed boxes, allowing it to feed on thin species of Daedalea, Bjerkadera adusta, Trametes versicolor, and, its particular favourite, Stereum hirsutum. It also nibbled on Armillaria mellea and Suillus grevillei, and partially consumed some Amanita rubescens. It was not thrilled, however, when offered Hypholoma fasciculare. Though it politely fed briefly on this mushroom, it did not agree with it at all and the plasmodium, which was clearly ailing, did not look itself again until it had been rejuvenated with a fresh piece of Stereum hirsutum.

I found this clutch in the winter.

During Lister’s year of experimentation with this plasmodium, numerous colonies made the change to sporangia. Others colonies, however, though being given exactly the same conditions as the ones that had matured, continued to stream and feed. Lister was unable to discover why some chose to form sporangia while others did not. And nor have I.

Weathered Badhamia utricularis

This spring’s batch of plasmodium that I brought home swarmed over the oyster mushrooms for several days until it had turned them into a pool of mushroom-shaped muck and then it just went pfft. Total dud. Though the plasmodium of B. utricularis is capable of forming dormant sclerotium that can be revived when moistened, my last plasmodium simply shriveled up and died.

Badhamia utricularis spores & capillitium

According to Lister’s notes, he never offered his plasmodium pets any sort of Pleurotus. I wish he had so I could read his observations. In just two years, I’ve found it feeding on Pleurotus populinus three separate times, so obviously the organism takes some pleasure in eating it. I believe other people have found B. utricularis on Pleurotus as well, other people who have jumped on a Physarum polycephalus bandwagon for no other reason than their having found an extensive yellow plasmodium engulfing a mushroom or other fungus on a log. But I think it’s a fool’s game to try to name a plasmodium to species without having the proof of sporangia. Pick it up, I say. Take it home. Enjoy the antics of your new “pet” until it chooses to reveal who it really is!

A massive expanse of Fuligo septica plasmodium like this could be 
mistaken for either Physarum polycephalum or Badhamia utricularis.

References & Resources:

Lister, Arthur. Notes on the Plasmodium of Badhamiautricularis and Brefeldia maxima Annals of Botany, Volume 2 1906 

Wired magazine's article about Physarum polycephalum & Tokyo rail system

Scientific American's article about Physarum polycephalum and mazes

http://www.scientificamerican.com/article/brainless-slime-molds/

Quentin D. Wheeler, A New Species of Agathidium Associated with an "Epimycetic" Slime Mold Plasmodium on Pleurotus Fungi (Coleoptera: Leiodidae-Myxomycetes: Physarales-Basidiomycetes: Tricholomataceae). The Coleopterists Bulletin Vol. 41, No. 4 (Dec., 1987), pp. 395-403

*Lincoff, G. The Audubon Society Field Guide to North American Mushrooms, 1981 – In Lincoff’s defence, he does not say exactly what Wheeler says in the Audubon Guide. What he says in the entry for Physarum polycephalum is that they can be found “on dead wood and fleshy fungi,” and, under the entry for Pleurotus ostreatus: “It is sometimes covered by the yellow early stage of a slime mold.”

This paper is “based on greenish yellow plasmodium collected on pilei of Pleurotus sapidus,” material that was cultured and proved to be P. polycephalum:

Howard, F. L., The Life History of Physarum polycephalum. American Journal of Botany Vol. 18, No. 2 (Feb., 1931), pp. 116-133