Horsetail (thing)

Horsetails are found primarily in swamps, river banks, or other areas with damp soil.

Since its stems can be used to clean cookware, or as substitute sandpaper, you should know how to identify the plant. Horsetails look a bit like rushes, they have a single stem running straight out of the ground. This stem is divided into sections, smaller branches radiate from the joints. It has a single large cone-like fruit at the top of the stem.

It should be noted that the stems of horsetails are poisonous, do not eat them.

UPDATE: It has been brought to my attention that the plant I wrote about was Equisetum hymale. There are over 20 different species of horsetail in the family Equisetaceae. Some species, such as Equisetum arvense are actually diuretic and can be used medicinally. Some species contain nicotine as well. How to go about telling them apart is beyond me. My advice: go to the store and buy a diuretic if you need one, and don't try smoking this thing...

Sources:
Hall, Alan. The Wild Food Trail Guide. Holt, Rhinehart, and Winston. 1945.