Equisetum aren’t the only organisms that use silica in their cell walls. Algae in the phylum Chrysophyta (golden-brown algae) use it to make “seeds.” Golden-brown algae are often found in ponds and shallow lakes that freeze from top to bottom in the winter. How is the poor little alga going to eat or swim around in a block of ice? It cannot! This could lead to a huge tragedy involving many many dead algae. But golden-brown algae just pack up all the important parts into an itsy bitsy glass box (called a statospore), snuggle up in the muddy pond bottom, and wait until the ice melts.