Symphyotrichum defoliatum (formerly Aster bernardinus) is a species of aster known by the common name San Bernardino aster. It is endemic to Southern California, where it is known only from the San Bernardino and San Gabriel Mountains of the Transverse Ranges, and part of the Peninsular Ranges to the south. It grows in grassland and meadow habitat and in disturbed areas. This is a perennial herb growing from a long rhizome to a maximum height near one meter. Leaves are widely lance-shaped to oblong and pointed, the largest ones near the base of the stem reaching up to 12 centimeters long. The stem and leaves are roughly hairy. The inflorescence is an array of flower heads with many narrow white to light violet ray florets around a center of golden disc florets. The fruit is a hairy achene with a long pappus.