A Nostoc Tour de Force
Hort Shorts
Authors
Joe Boggs
Published on
May 3, 2017
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 starslime. 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.