As I was walking, I noticed a pile of greenish black, jellylike globs. It looked like plant parts had been stirred together and left to rot, but there was no odor of mildew or fermentation. I took a few more steps and saw another pile, and then another. I then realized they were all connected. There was a vast network of blobs emerging from the leaf litter.
This is Nostoc commune, a terrestrial blue-green algae, or cyanobacteria.
But blue-green algae isn’t algae, nor a plant, nor a fungus. It is similar to bacteria, but is able to use photosynthesis to produce its own food.. The structures we see are actually chains of microscopic, single-celled organisms.
Nostoc enjoys a good meal of phosphorus, which is often found in plant foods. However, it also produces its own food, using the energy of the sun. This cyanobacteria produces chlorophyll, which allows it to convert nitrogen into a useable form. All living things, including humans, use nitrogen to make amino acids and proteins. Animals get their nitrogen by eating plants or other animals.
Nostoc is extremely resilient. It can live in hot and cold temperatures, and withstand drought and flooding. When it dries, it looks like dark-green or nearly-black paper, or an irregular leaf that has been pressed in a book. When it rains, it swells and once again becomes active. That is why we notice it after periods of heavy rainfall.
In addition to chlorophyll, it also produces phycocyanin, a blue pigment which allows it to capture light even in low-light conditions. It can also tolerate extremely bright sunlight, being resistant to extreme radiation.
Nostoc forms symbiotic relationships with plants, mosses, and those fungal species which combine with algae to create lichens. It is particularly important to cycads, an ancient family of toxic plants predating dinosaurs. Young cycad roots grow upward to accommodate Nostoc, allowing it to colonize around the roots in sunlight. Nostoc then enters the roots themselves, which swell and become tuberous to better house Nostoc and other beneficial microbes. Once inoculated, mature cycad roots may grow farther below ground.
Nostoc reproduces in several ways—by breaking off, cloning itself, or through the production of sporelike cells called akinetes, which are resistant to temperature changes and drying.
Nostoc is considered non-harmful, although swollen Nostoc is extremely slippery and can be dangerous to walk across. In Asia, it is often eaten or used medicinally. However, Nostoc produces a toxin which can lead to neurological conditions in animals that consume it over time, including predators that eat it secondarily.
Common names for Nostoc include Star Jelly, Star Shot, and Star Slime. During the Middle Ages, it was believed that Nostoc came from the dust of shooting stars. It may also be called Witch’s Butter or Witch’s Jelly, although these common names may also refer to an unrelated gelatinous fungus.
From now on, when I walk past these green-black blobs, I’ll have new appreciation for them. These life forms are some of the oldest on our planet, and can survive when little else can. They also help plants to grow, retain water in the soil, and produce oxygen for all to breathe. In fact, cyanobacteria is believed to have generated oxygen on Earth, allowing other life forms to gradually evolve. Although humble in form, Nostoc and its relatives are some of the most important organisms on our planet.
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