Symphyotrichum greatae (formerly Aster greatae) is a species of aster known by the common name Greata's aster.
It is endemic to the San Gabriel Mountains of Southern California, where it grows in damp areas in the canyons of the southern slopes above the Los Angeles Basin.
Symphyotrichum greatae is a colonizing perennial herb growing from a long rhizome. It produces upright to erect stems usually 50 to 120 centimeters tall, but known to approach two meters. The leaves are mostly oval in shape and pointed, the lowest ones up to 15 centimeters long. The leaves and parts of the stems are hairy.
The inflorescence is an open array of flower heads amidst leaflike bracts. The flower head contains many pale violet to nearly white ray florets and a center of yellow disc florets. The fruit is a hairy achene.