Aristolochia watsonii (Watson's Dutchman's pipe, southwestern pipevine, Indian root, snakeroot) is a perennial plant in the birthwort family (Aristolochiaceae), found growing among plants of the Arizona Uplands in the Sonoran Desert.:138 The plant is inconspicuous,:138 small and hard to spot, but can be found by following the pipevine swallowtail (blue swallowtail, Battus philenor) which lays eggs on it.
It grows as vine with scrambling stems that create a dense, tangled mat over the years when growing on open ground.:138
According to one source, stems are 6 to 18 inches (15 to 46 cm) long, with greenish-brown arrowhead shaped 14 to 2 12 inches (0.64 to 6.35 cm) leaves.:138 Another source states stems can reach 3 feet (0.91 m), in dense mats that are 1 to 2 feet (0.30 to 0.61 m) wide. It drops its leaves in the fall and winter (cold-deciduous), and loses stems as well as leaves in a freeze. In full sun and drought conditions, leaves turn from green to purple-brown.
It has "bizarre" looking, musky smelling flowers, which resemble the ear of a rodent.:138 It blooms from April to October. 1 to 1 12 inches (2.5 to 3.8 cm) flowers are shaped like a rodent's ear:138 are green or burgundy-brown outside to the ear rim, then green speckled with burgundy-brown inside, with hairs on the opening ear rim.:138 Flowers last 1-2 days.
Fruits are capsules having five vertical ribs with triangular shaped flat and black seeds in each of five compartments.
Flowers shaped and smelling like a rodent's ear attract small blood-sucking flies, which are deceived by the appearance and odor and get trapped in the convoluted flower form for a day, then escape to pollinate another plant.:138 It attracts the pipevine swallowtail, and is where the butterfly gets its distasteful toxins that protect the butterfly from predation. The caterpillar may eat all of the leaves on a plant, but they then grow back.
All parts of this plant are toxic to humans.
It is found from Arizona to western Texas, in mountains at elevations from 2,000 to 4,500 feet (610 to 1,370 m).:138
Native Americans believed it could be used to treat snakebites, hence its common names Indian root or snakeroot.:138 It is currently found in some nurseries that feature native plants as it is a good landscape plant in a butterfly garden.