For everyone who wants to know why it's endangered (like i did): Because of a fungus that originally grew on the japanese chestnut variant (starting in the early 1900s), to which the american chestnut has no resistance - it is estimated that in in first half of that century, three to four billion tree died to that fungus. In the original geographic range of the American chestnut, only 4 mature trees remain. There are still some root systems that sprout saplings, but they get killed off by the fungus quickly. There are some enclaves in other areas that still have a few hundred, like in northern Michigan