Machaeranthera canescens (syn. Dieteria canescens) is a species of flowering plant in the aster family known by the common names hoary tansyaster and hoary-aster. It is native to western and central North America, where it is a common plant in many regions and habitat types. It is a woolly-haired, hairy annual or perennial herb with one or more branching stems sometimes exceeding a meter in height. The linear to oblong leaves may reach 10 centimeters long near the base of the stems, their edges usually serrated or toothed. The flower cluster bears one or more flower heads lined with several layers of pointed, curling or curving phyllaries. The head has a center of many yellow disc florets and a fringe of blue or purple ray florets each 1 to 2 centimeters long. The fruit is an achene around 3 millimeters in length tipped with a pappus of long hairs.