Tuesday, 18 February 2014
Slime mold hardly dog vomit or scrambled egg
These pink blobs in Melbourne's Royal Botanic Garden are slime molds (or moulds). They are not fungi, or for that matter algae, plants or animals.
'Slime molds' is not what we call a natural group. That is, organisms called slime molds aren't the only descendants of a common ancestor. Natural groups are things like flowering plants, primates and Entwisleiales. Unnatural groups are things like algae, trees and cuddly animals - these are terms of (sometimes great) convenience.
The slime molds can be divided into various convenient, and some cases natural, subgroups. The plasmodial slime molds (or Myxogastria) are microscopic, often swimming (they can have flagella) cells that fuse together to form a great big cell with thousands of nuclei (each one the 'brain' of the single swimming cell). The big cell, the slimy moldy bit, is called the plasmodium. These you can keep calling slime molds.
The cellular slime molds (or Dityostelia) are microscopic non-swimming cells that only every now and then aggregate into a 'slug', called a pseudoplasmodium. Unlike its plasmodial colleagues, the individual slime-mold cells maintain their integrity and the slug is a little like a many-celled organism such as mushroom, rabbit or...slug. They are better treated as 'social amoebae' rather than slime molds.
There are other smaller groups, more or less related to these two. The slime nets (or Labyrinthulomycetes) are these days not to be mentioned in the same sentence (apart from here) as the slime molds. These mostly marine creatures consist of tubes along which cells glide along looking for food. The slime nets are related to, and possibly part of, the Heterokontophyta, which includes diatoms and kelp (algae) and phytophthora (water mold).
All of these organisms produce spores when things get tough. Sometimes the spores are clustered on the top of a stalk, other times in round puff-ball like structures like these (at the end of my forefinger).
This particular slime mold is called Lycogala epidendrum, a plasmodial type. It's growing in a pot of Swainsona in the nursery at Melbourne's Royal Botanic Gardens. The picture at the top of the post was taken by David Robbins, a few weeks before I saw and photographed them in early January.
Back further in time, before David Robbins - and Val Stajsic the Identification Botanist who lived up to and extended his job title by identifying it as Lycogala epidendrum - noticed the fruiting bodies (called aethalia), the slime mold would have consisted only of tiny red cells. I think the fruiting body is the entirety of the plasmodium stage in this case*.
Those slime molds that form big slimy masses of various kinds - dog vomit, red raspberry, scrambled egg, wolf's milk - can cover up to a square metre or so in some species. They not only spread but move, being able to track down food (bacteria, yeasts and algae) or repel themselves away from something nasty at a rate at least 10 times faster than a plant. Not quite your typical animal speed but fast for a slimy mass I'm sure you'll agree. Our slime mold just stayed where it was, in the pot.
Notes: Information sourced from among other places University of California Museum of Paleontology, The Eumycetozoan Project and an article published in the Proceedings of the National Academy of Sciences of the USA on the origin and evolution of slime molds by Sandra Baldauf and Ford Doolittle. This mention of Doolittle reminds me that a slime mold shouldn't really be part of TalkingPlants (or TalkingAnimals to be fair) but I'm willing to include anything that is rather sluggish and grows in a pot...
*Postscript: Myxomycetes enthusiast and author of the beautiful and informative book Where the Slime Mould Creeps: the Fascinating World of Myxomycetes, Sarah Lloyd, wrote to me in October 2015 saying that in at least some species the plasmodium persists outside the fruiting body. Sarah has observed flushes of sporangia produced from the same patch of a fallen log every time it (frequently) rains in forests near to where she lives in Tasmania. Other times, if the fruiting bodies are removed or lost, there is no reappearance for at least a year. So my Lycogala fruiting bodies may or may not be the whole kaboodle!