Myrica hartwegii is a species of shrub in the bayberry family known by the common name Sierra sweetbay, or Sierra bayberry. It is endemic to the Sierra Nevada of California, where it grows in moist areas, such as streambanks, in the foothills and lower slopes up to a maximum elevation of 1500 to 1800 metres. This deciduous shrub grows one to two meters tall with purple-black branches and twigs studded with yellowish resin glands. The leaves are widely lance-shaped to oval with blunt tips. They are up to about 10 cm long and about 3 wide, and they are usually edged with a few shallow teeth. They have scattered hairs and are densely coated in resin glands. The male and female flowers are arranged in separate spikelike inflorescences. The spherical, slightly waxy fruit is just under 2 mm wide and is dotted with glands.