Echinopsis pachanoi (syn. Trichocereus pachanoi), the San Pedro cactus, is a fast-growing columnar cactus native to the Andes Mountains of Ecuador and Peru between 2000–3000 m in altitude. It is also found in Argentina, Bolivia and Chile, and it is cultivated in other parts of the world. Uses for it include traditional medicine and traditional veterinary medicine, and it is widely grown as an ornamental cactus. It has been used for healing and religious divination in the Andes Mountains region for over 3000 years. It is sometimes confused with its close relative, Echinopsis peruviana (Peruvian torch cactus).
Echinopsis pachanoi is native to Ecuador and Peru. Its stems are light to dark green, sometimes glaucous, with a diameter of 6–15 cm (2.4–5.9 in) and usually 6–8 ribs. The whitish areoles may produce up to seven yellow to brown spines, each up to 2 cm (0.8 in) long; the plant is sometimes spineless. The areoles are spaced evenly along the ribs, approximately 2 cm (0.8 in) apart. Echinopsis pachanoiis normally 3–6 m (10–20 ft) tall and has multiple branches, usually extending from the base. The tallest recorded specimen was 12.2 metres (40 ft) tall. White flowers are produced at the end of the stems; they open at night. The flowers are large, around 19–24 cm (7.5–9.4 in) long with a diameter of up to 20 cm (7.9 in). There are black hairs along the length of the tube leading to the flower. Oblong dark green fruits are produced after fertilization, about 3 cm (1.2 in) across and 5–6 cm (2.0–2.4 in) long.