This week in Roy's Redwoods started out warm and sunny, with high temperatures in the mid-60s° F (18° C,) but by Tuesday we'd settled into a pattern of overnight showers giving way to mostly-cloudy days, with daytime highs in the upper 50s° F (14°C) and nighttime lows in the low 50s° F (10°C.)
It's the perfect time to meet some slime molds!
Wait, what the heck is a slime mold?
Despite having a name with the word "mold" right there in it, slime molds are not fungi. Slime molds are members of Kingdom Protozoa; more specifically, I'm referring to plasmodial slime molds belonging to Class Myxomycetes.
Plasmodial slime molds are amoebas. An amoeba is a single-celled organism that can project temporary armlike extension known as a pseudopod, and in my opinion, they're biological paragons of elegant simplicity. Consider an amoeba:
This is a slime mold plasmodium I've named Loggo, on account of the fact that they're growing on a log. Loggo is a single cell, a great big sack of cytoplasm surrounded by a cellular membrane (but no cell wall.) If you could look inside Loggo, you wouldn't find much in the way of organelles - no mitochondria, no endoplasmic reticulum, no chloroplasts. The organelles inside an amoeba are limited to food vacuoles (which contain and digest food,) contractile vacuoles (which control water pressure in the cell,) and nuclei (which contain the genetic material.) A branched plasmodium like Loggo here may have up to 10 million nuclei.
Here is Loggo four days later, having crawled halfway across the face of the log. Slime mold plasmodia move very slowly - about 2 mm per hour - which makes them interesting to watch over a period of days (or via time-lapse video.) Loggo's locomotion process is called cytoplasmic streaming, or just streaming for short. It's powered by a system of actin-myosin contractile fibers fueled by ATP - roughly the same way our muscle cells work.
Here is another slime mold plasmodium, whom I've dubbed Shroomie. The first time I encountered Shroomie, they had just begun to cross the underside of an Artist's Conk (Ganoderma brownii) mushroom. The plasmodium is super-concentrated on the mushroom because it's a food source. The bulk of a slime mold's diet is usually bacteria, but they also dine on fungi (spores, hyphae, and fruiting bodies,) as well as yeasts and algae.
This is Shroomie on the following day, continuing to eat their way across the Artist's Conk. Slime molds consume their food in a process called phagocytosis. A pseudopod extends to surround and envelop the food inside a vacuole, where it is then digested. Amoebas are the Kirby of the microbial world, if you think about it.
Here is Shroomie two days after the previous photo, beautifully plumped up after feasting on fungus. See the globs forming on the bottom-right? This is where the plasmodium is beginning to transform into the reproductive form - the sporangia!
Sporangia are the reproductive structures of the slime mold. The photo above shows Hanging Slime Mold sporangia in its early stage of development, fresh from the plasmodium. The formation of sporangia can be triggered by changes in pH or temperature, or by depletion of food sources.
As the Hanging Slime Mold sporangium matures, the stalk thins and lengthens.
A bean-like glob consolidates at the tip of each stalk. This is the sporotheca, the part of the sporangium that holds the spores. A single Hanging Slime Mold plasmodium can product anywhere from a single to hundreds of sporothecae, each measuring 0.5 - 1 mm in diameter.
As the Hanging Slime Mold sporothecae develop, they begin to change color. The yellowy-orange of the plasmodium gives way to taupe, and for a few hours, they do a very good job of looking an awful lot like nattō.
Here is the same Hanging Slime Mold as shown above, four hours later. The sporothecae have darkened dramatically. Inside each tiny glob, hundreds of spores are developing - single-celled "seeds" of the next generation of slimes.
Mature Hanging Slime are deep blue-violet when wet, as in the background of the above photo. When dry, they can range from pale slate-gray...
...to blueberry-blue, depending on conditions and lighting (they are iridescent.) Hanging Slime Mold is pretty easy to spot in the plasmodial or early sporangial forms, when they're brightly-colored, but the blue-gray mature ones are often tough to see without a flashlight, even in on a sunny day. I usually find them hanging under logs.
Badhamia isn't the only slime mold active in Roy's Redwoods this week. I also watched these Trichia decipens sporangia develop over a few days. I found them growing on a decaying bit of wood in the same "slime mold hotspot" area as Loggo and Shroomie. They're very small - about a millimeter in diameter, at most.
These are the same Trichia as above, a day later. The cream-colored sporothecae are now a pinkish-buff, but they're not quite mature yet.
Two days after the previous photo, the Trichia are fully mature (or very close to it.) These are an olive-yellow color, but this species can also turn brown or dull yellow. The spores inside are olive-yellow.
Arcyria ferruginea is another slime mold I found growing in the "hotspot" this week. This species undergoes a wild transformation, from pale-pink plasmodium to hot-pink young sporangia before turning brick-red (as above) and, finally, a deep mustard-yellow.
We had a great big flush of Honeycomb Coral at the start of the rainy season. I still see them pop up after a shower, though not as many as that first flush. In the Honeycomb Coral sporangia, it's the lack of color that's spectacular. When they begin to form, they look a bit like semi-opaque tri beads. Most are whitish in color, but they can also be pale yellow, pink, blue, or green, depending on environmental conditions.
As the branched sporangia grow, they become less opaque.
At full maturity, Honeycomb Coral almost transparent - like they're made of ice! This is one of the easiest slime molds to find in Roy's Redwoods after a big rain event, since they often grow in plain sight (rather than under wood.) They're small enough that they can be easily mistaken for mold, though, so it pays to look closely.
Alas, some slimes remain anonymous to me despite my best efforts. The slime mold pictured above is in the process of transforming from plasmodium to sporangia, but when I went back to check on them the next day, they'd been obliterated by heavy rain - possibly drowned, since these organisms do need oxygen to live. I can't identify them at this stage, but I think this may be Stemonitopsis typhina.
The sporangia above were growing in my "hotspot," but a fuzzy mold infection makes it tough to see them well enough to identify (my best guess is Trichia decipens.) This is a common occurrence with slime molds, and I'm always tickled when I see it, since plasmodial slime molds are known to eat fungi.
Like I always say: Sometimes you eat the fungus; sometimes the fungus eats you.
Previously: 20 - 26 January 2019