Within the category of “what is it?” lives a strange-looking organism called Nostoc. I first saw it a few summers ago when several people brought in samples of a green, jelly-like substance growing in their lawns, and someone has brought it to my office every year since then. After a bit of digging the first time, I identified the stuff as Nostoc sp., a genus of cyanobacterium formerly classified as blue-green algae. Nostoc has many colorful names including witches’ butter, mare’s eggs and meadow ears, among others. In fact, one of the earliest names for it was star jelly, based on the belief that it was a remnant of shooting stars fallen to earth.

Following a period of rain, it may appear suddenly in lawns, pastures, paved surfaces, roofs or stones. Michigan State University Extension has even reported Nostoc a problem in commercial nursery production. It can be hazardous on paved surfaces as it is very slippery when wet. When found in lawns, it is generally on a site where the grass is growing poorly due to severe compaction, overwatering or both. It has not caused the lawn’s decline; it has simply colonized an area where it has favorable conditions to grow. Poor drainage, compacted soils and fertilizers containing phosphorus create a favorable environment for colonies of Nostoc.

Nostoc can be difficult to get rid of. From its gelatinous, green state, it dries to a black crust that comes back to life when there is sufficient rain. To discourage its growth, improve drainage and eliminate phosphorus fertilizers. Products that contain potassium salts of fatty acids may be used to kill it in lawns. Three such products are Bayer Advanced Moss and Algae Killer, Safer Brand Moss and Algae Killer, and Garden Safe Moss and Algae Killer Concentrate (there may be others). They must be used carefully according to label directions, or damage to turfgrasses may occur. Core aerating the lawn to reduce compaction may help, but tilling the soil will merely break it into more pieces and encourage its spread. For paved surfaces and small patches in lawns, shoveling it up and discarding it in a landfill may be an option.

Although we may not appreciate it growing in our lawns or on our pavement, consider that Nostoc possesses many redeeming properties. Several Nostoc species have been used as both a food and medicine for centuries, and have more recently been evaluated for their pharmaceutical properties, including antibacterial metabolites, cholesterol regulation and control of certain cancers. They also have potential for being utilized to produce biofuels. They have the ability to fix nitrogen from the air and contain pigments which allow them to use the sun’s energy for photosynthesis. The chloroplasts in plants are believed to have evolved from cyanobacteria. They contain compounds capable of absorbing ultraviolet light, which allow them to withstand extreme UV radiation. There are species adapted to water and land that are able to withstand extreme temperatures, like those present in pools of water near active volcanoes, or in the Artic. Cyanobacteria were most likely the first organisms on earth to release oxygen into the atmosphere, setting in motion the development of higher plant and animal forms.