Polystichum lemmonii is a species of fern known by the common names Lemmon's holly fern and Shasta fern. It is native to western North America from the Sierra Nevada of California north to Washington. It is also known from British Columbia, where there is a single occurrence in the mountains above the Okanagan Valley. It grows in mountainous habitat on ultramafic rock substrates, often in serpentine soils. This fern produces several narrow, erect lance-shaped leaves 10 to 35 centimeters long. Each leaf is made up of many oval leaflets which are overlapping, folded, and twisted such that the leaves may appear almost cylindrical. Their edges are cut or toothed.