The horsetail family is also known as the scouring rush family.  Horsetails generally have hollow, grooved and jointed stems that contain silica.  They are rough or harsh to the touch.  Their slender green branches have been mistaken for leaves.  They are whorled around the stem.  The leaves are a series of teeth.  They reproduce by spores and creeping roots, not seeds, and usually need abundant moisture to accomplsih this task.  The spores are found in cones at the stem tip.