The main difference between the spruce-fir forests of Southern Appalachia and the spruce-fir forests in northern latitudes is the dense broad-leaved understory of the former. The spruce-fir understories of the Smokies are home to catawba rhododendron, mountain ash, pin cherry, thornless blackberry, and hobblebush. The herbaceous and litter layers of the spruce-fir forests are poorly lit year-round, and are thus dominated by shade-tolerant plants such as ferns, namely mountain wood fern and northern lady fern, and over 280 species of mosses.