|Equisetum hyemale, the scouring rush horsetail, one of the many species of horsetail. It has several other common names|
|A horsetail fruiting body|
Though this plant is happiest in moist to wet soil, it can also grow in standing water several inches deep. This species can grow to as tall as five feet, and is in the form of a hollow reed-like body with tiny leaves forming grew sheaths at the plant's joints. Since the leaves are so small, photosynthesis mostly occurs in the stem. Fruiting bodies are similar to pine cones, and these plants are seedless and do not produce flowers.
The body of the plant is high in silica, and was used by settlers to scour cookware, which explains the origin of the common name "scouring rush."
Sources are the United States Department of Agriculture and the Kemper Center for Home Gardening from the Missouri Botanical Garden. Images are from Wikimedia Commons under creative commons licenses: one, two