Our warm, wet spring has provided ideal conditions for the rise of a strange looking organism with a scientific name that sounds like a '70s California happening: Nostoc commune. This bizarre organism may look as if an agglomeration of rubbery yellowish-green to bluish-black material is "bubbling-up" in the open spaces in Ohio landscapes as well as gravel driveways. During periods of dry weather, the odd-looking masses collapse and turn black.
The otherworldly appearance of this world-wide organism is responsible for several common names. It was once believed the alien-looking masses originated from the dust of shooting stars (a.k.a. meteors) which accounts for the common names of star-jelly, star-shot, and star-slime. Other common names such as "witch's-butter" are self-explanatory. The bottom-line is that star-jelly is not toxic; it causes no harm to plants or animals including harm to the health of concerned Ohio landowners. However, the mucoid mates can become slippery when wet, so tread carefully.
Fascinating Background Information (Optional Reading):
Star-jelly is fascinating because it belongs to a group of bacteria called cyanobacteria (a.k.a. Cyanophyta) that have photosynthetic pigments in their cytoplasm to perform photosynthesis. The pigments impart a slight blue-green color to the cells. Since the bacteria act like plants by producing their own "food" (polysaccharides) and because they generate oxygen, cyanobacteria were once incorrectly called "blue-green algae."
However, algae as well as other plants (and animals) are "Eukaryotes" meaning their nuclei are gift-wrapped in a membrane. Cyanobacteria lack membrane-bound nuclei; a condition that makes them a "Prokaryote." There are several interesting evolutionary connections between prokaryotes and eukaryotes. Biologists generally agree that chloroplasts in plants have their ancestral origins with cyanobacteria through an evolutionary process called "symbiogenesis."
Cyanobacteria also have a few other interesting tricks up their prokaryotic sleeves. They have specialized cells called heterocysts that can grab nitrogen out of the atmosphere in a process called "nitrogen fixation" to convert the nitrogen into molecular forms that make the element available for the bacteria as well as plants. For this reason, some cyanobacteria may be found growing on the surfaces of plants, including certain algae, which once added to the confusion with learning the true identity of these unusual bacteria. Star-jelly (Nostoc commune) was also found to have specialized pigments in their cells that absorb UV light to protect against UV radiation. This allows star-jelly to survive some extreme environmental conditions which is one reason this cyanobacterium enjoys a world-wide distribution.
Why Does it Look So Weird?
Star-jelly is a terrestrial type of Nostoc cyanobacteria. There are other species that are solely aquatic. The ability for star-jelly to produce its own food requires exposure to sunlight. This, coupled with the ability to grab nitrogen from the air, is why star-jelly is commonly found creeping over open surfaces including openings in turfgrass or gravel driveways.
The overall appearance of star-jelly varies with environmental conditions, particularly with the availability of "free" moisture in the form of rainfall. At the microscopic level, star-jelly is composed of cells that link themselves in a bead-like fashion to form unbranched hair-like structures called "trichomes" which are then surrounded by a gelatinous sheath. The trichomes group together, along with their associated heterocysts, to form "colonies." This is where microscopic becomes macroscopic.
During wet weather, the gelatinous sheaths collectively swell to produce the yellowish-green to bluish-black, bubbly, mucoid structures characteristic of star-jelly. Under dry conditions, the structure collapses to form blackened, rubbery-looking mats. However, the microscopic cells remain viable and can survive lengthy periods of dry weather to reappear when moisture returns.
The need for sunlight and free moisture is the Achilles heel of star-jelly. Improved drainage as well as increased shading can cause star-jelly to slowly fade away. A good long-term management strategy includes taking steps to thicken turfgrass as well as dealing with drainage issues. Using a shovel to remove colonies from open locations such as gravel driveways will only provide short-term relief because the shovel is a macroscopic tool that's targeting a microscopic problem.
Final Fun Facts:
The name of the star-jelly genus as well as the names for the taxonomic order (Nostocales) and family (Nostocaceae) have a common root. Various references say "nostoc" was coined by the 15th century Swiss physician and scientist Paracelsus who was actually born Philippus Aureolus Theophrastus Bombastus von Hohenheim.
However, I could find no references for what "nostoc" actually means; perhaps it's Ewe yuck. I did find that Philippus et al. changed his name because he wanted to be viewed as a rival to ancient medical authorities; Paracelsus translates to "equal to Celsus." I think it may have actually been to avoid being called Bombastus or perhaps Philippus ad nauseum. References consistently describe him as a vain, difficult man. He was appointed Professor of Medicine at the University of Basal, Switzerland, in 1526 and then exiled from Basel in 1538.