They are very common in soil but rare in aquatic ecosystems. This makes sense if you view the endospore as an adaptation to environments that dry out occasionally. Most of the endospore formers are grouped into two genera, Bacillus and Clostridium . Bacillus All are aerobic or facultative aerobes. They are often distinguished by the substrates that they can ferment.
Endospores survive for years in a dormant state.
There are some recent claims that endospores can survive for millions of years - but these claims are controversial. Read this article on a Bacillus sp. Diversity of microorganisms isolated from amber. Sporosarcina - forms distinctive tetrads . . The high GC group can be broken into about ten major genera and were traditionally divided into the Coryneform Bacteria and the Actinomycetes.