Tonestus lyallii is a species of flowering plant in the aster family known by the common names Lyall's goldenweed, Lyall's serpentweed and Lyall's tonestus. It is native to western North America, particularly in the Rocky Mountains and the mountain ranges of the Pacific Northwest with scattered occurrences between. It is a perennial herb growing in clumps or short bunches not more than about 15 centimeters tall, the stem branching from a tough caudex. The leaves