Thelesperma megapotamicum is a perennial species of flowering plant in the aster family known by the common name Hopi tea greenthread and rayless greenthread. It is native to sections of the Americas, including the central United States, where it grows in many types of habitat. It is a perennial herb producing a slender, branching stem 30 to 60 centimeters tall or more. The leaves are narrow, mostly compound with linear or threadlike segments measuring a few centimeters long. The inflorescence bears several flower heads each in a cuplike involucre of phyllaries with purple-tinged, pointed lobes with white edges. The head contains many yellow or orange disc florets, and sometimes one or more yellow ray florets, although these may be absent.