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).

Vines emerge from a large, hard tuberous root which can reach several meters in length and weigh in excess of 100 kilograms (220 lb).

The fruit is spherical to oblong, 6–8 centimeters (2.4–3.1 in) in diameter, and suspended from a long, wrinkled stem.

Some plants have smooth fruit with dark green veins running from top to bottom.

Fruit begin to form in spring and ripen as the vine dies from the heat and drought of late spring/early summer.

Taw manroot grows most vigorously by streams or in washes but can also be successful in dryer areas, at elevations up to 1,600 meters (5,200 ft).