NEW YORK (Reuters) - The United States and China want to expand trade regulations to protect Asian yew trees, a plant that provides the compound for one of the world's top-selling chemotherapy drugs but is threatened by poaching. Chinese herbalists have used trees of the taxus species, also known as yew trees, for centuries to treat common ailments. In the late 1960s, scientists in North Carolina found that extract of yew bark fought tumors, and in the early 1990s, the U.S. government approved the use of paclitaxel, also known as taxol, by drug company Bristol-Myers Squibb for chemotherapy. Taxol, whose...