Nostoc:

Nostoc is a genus of cyanobacteria.  It forms colonies encased in a gelatinous sheath.  It can be found in soil, on rocks, and in lakes and ponds.  Nostoc can live in extremely cold or arid conditions.  This ability to survive these conditions makes them particularly interesting to scientists.  Nostoc also has the ability to lie dormant for long periods of time and recover metabolic activity after it is rehydrated.  When Nostoc is in the dry soil it may not be visible to the eye.  However, after it rains, the Nostoc will expand and form visible spherical colonies.  There are over 200 species of Nostoc, some of which are edible and are considered a delicacy in China.