Fungi have also been transported, such as the one responsible for Dutch elm disease, killing American elms in North American forests and cities, where many had been planted as street trees. Some of the invasive species have become serious ecosystem and economic problems after establishing in the New World environments. A beneficial, although probably unintentional, introduction is "Saccharomyces eubayanus", the yeast responsible for lager beer now thought to have originated in Patagonia. Others have crossed the Atlantic to Europe and have changed the course of history. In the 1840s, "Phytophthora infestans" crossed the oceans, damaging the potato crop in several European nations. In Ireland, the potato crop was totally destroyed; the Great Famine of Ireland caused millions to starve to death or emigrate.