Nostoc

Nostoc appears mysteriously after rains—gelatinous masses seeming to materialize from nowhere, leading to folk names like 'star jelly' and 'witch's butter.' This cyanobacterium survives complete desiccation, remaining dormant for years then reviving within minutes when water returns. Colonies can tolerate extreme temperatures, UV radiation, and even the vacuum of space. Nostoc represents cyanobacterial toughness taken to extreme.

The key to Nostoc's resilience is extracellular polysaccharide—the gelatinous matrix that gives colonies their distinctive appearance. This matrix retains water during drying, protects cells from UV damage, and maintains structural integrity through repeated wet-dry cycles. Cells enter dormancy by producing protective pigments and stabilizing membranes. The whole system can shut down indefinitely and restart rapidly when conditions improve. This intermittent strategy suits environments where favorable periods are unpredictable and brief.

Nostoc's partnership versatility rivals its environmental tolerance. It forms symbioses with fungi to create lichens, with liverworts, with hornworts, with the fern Azolla, and with cycads. In each partnership, Nostoc provides fixed nitrogen while the host provides carbon and protected habitat. This promiscuity reflects Nostoc's generalist strategy—it doesn't commit to one host type but maintains capability to partner with whatever opportunities arise. The combination of stress tolerance and partnership flexibility makes Nostoc one of the most successful cyanobacterial lineages on land.