[5] Large and stout, this species reportedly exceeds 2 m (6.6 ft) in total length, although the verified maximum is 169 cm (67 in).

On the body, there is a series of 22-28 dorsolateral markings that are chocolate brown to black in color and boldly bordered in cream or white.

The ventral surface includes a dark brown to black stripe that starts at the neck and runs down to the tail tip.

In Brazil it is called boicoatiara, boicotiara (Tupi dialect), coatiara, cotiara (southern Brazil), cruzeira, cruzeiro, jararaca de agosto (Rio Grande do Sul, Lagoa dos Patos region), jararaca rabo-de-porco (Rio Grande do Sul), and urutu[4] or wutu.

In Argentina it is found in the provinces of Buenos Aires, Catamarca, Córdoba, Corrientes, Chaco, Entre Ríos, Formosa, La Pampa, Misiones, San Luis, Santa Fe, Santiago del Estero and Tucumán.

[4] Although Spix and Martius (1824) found that it had a reputation for being one of the most venomous snakes in Brazil, its bite "said to occasion almost certain death", the statistics tell a different story.

In his survey of 6,601 snakebite cases in Central and South America, Fonseca (1949) found that 384 were attributed to this species and that, of that number, only eight were fatal (2%).

[9] In a study by Baub et al. (1994) of the case histories of 32 patients bitten by this species and admitted to the hospital in Catanduva, São Paulo, Brazil, all developed local pain and swelling.

Silva Jr. (1956) includes a description of a Brazilian patient with gangrene on the hand and forearm that required amputation, as well as another bitten four years previously who had scarring over the anterior tibial compartment.

Abalos and Pirosky (1963) considered this species to be responsible for many of the total number of snakebite cases in Argentina and included a picture of a young boy, bitten below the knee, with the bare fibula and tibia exposed.