Marah watsonii, the taw manroot, is an uncommon species in the genus Marah endemic to central northern California. Its range is bounded by the eastern coastal foothills, the western foothills of the northern Sierra Nevada and Cascades ranges and from Lake Berryessa in the south to Lake Shasta in the north. Foliage. Taw manroot shares with all marah species non-twining stems and tendrils. Unlike other manroot species, however, Marah watsonii vines are nearly hairless with a glaucous, grey-green color. Vines appear in late winter or early spring in response to increased rainfall, and can climb or scramble to a length of 6 meters (20 ft).