Several species of thistles can be found in the northeast. The two most common I run into are bull thistle (pictured above) and Canadian thistle, which is a little smaller with narrower leaves. The thistle is one of my favorite plants because it is so useful. The stem and leaf petioles (i.e. leaf stem) can be eaten raw after you remove the spines. The spines can be removed by simply grabbing them and pulling downward (essentially stripping the spine and lower spines off of the stem. Doing this is kind of fun, and can be a relaxing way to pass a few minutes. The stem tastes like celery and has a celery-like structure. I find it sweeter than celery, especially if the plant is eaten earlier in the spring or summer.
The root can also be eaten after being boiled. I like the roots even more than the stems because they develop a nice texture.