Austrocylindropuntia subulata can reach heights up to 4 meters, with numerous branches. The elongated, slightly brittle branches are up to 50 centimeters long. The stems are marked by rhomboid to ovate bumps in a few spiral rows. At the tip of each bump is the areole, from which grow one to four straight, grayish-white spines up to 8 centimeters long. The awl-like rudimentary leaves are up to 12 centimeters long.