Horsetails are odd enough that long ago when I knew very few plant names, I saw one and asked "what is this?" The hollow jointed stems are not like much of anything else. I learned not just that it was a horsetail, but that its an ancient plant. My college textbooks spoke of fossiles from the Carboniferous, 300 million years ago, that are virtually unchanged in structure; the genus Equisetum might be the oldest surviving genus of plants on earth. There were horsetails 60 feet (18 meters) tall. Today there are still some in Mexico and Central America that grow to 20'. Wow.