This olive-green, jelly-like organism was the cause of a slip leading to an ankle injury for an Assynt resident recently, in their own garden! It is a species of Nostoc, a genus of cyanobacteria which have been around for about 3.5 billion years; they used to be known as blue-green algae.
Nostoc is not easy to control, especially when you consider it has survived everything from Ice Ages to volcanic eruptions. When dry this organism is simply a black crust but, given sufficient rain it comes to life again forming the gelatinous colonies seen in these photographs.
Although probably not appreciated by gardeners Nostoc does have numerous redeeming properties. A number of the species have been used as food and medicines for centuries and, more recently, they have been looked at for regulating cholesterol and the control of certain cancers. It is also most likely that cyanobacteria were the first organisms on earth to release oxygen into the atmosphere, and so setting in motion the development of higher plant and animal forms – some of which now slip on it!
As to the injury, both the ankle and the pride are pretty much restored but the Nostoc remains and awaits the unwary.