Tephrocactus alexanderi aka Dino Egg Cactus

Tephrocactus alexanderi is a small cactus from northwestern Argentina. It belongs to the cactus family, Cactaceae. Its native range includes La Rioja and Salta provinces. The Spanish common name is Bola de Indio. It grows in desert or dry shrubland. Wild plants grow and flower on very dry, rocky ground. Few other plants thrive in these harsh sites.

This succulent subshrub forms low cushions of spiny, rounded branches. Some plants grow upright rather than hugging the ground. The grey-green stems have a bumpy surface and separate into joints. These joints can be round, egg-shaped, or short cylinders. They measure 0.08–0.16 feet [0.025–0.05 metres] long. Their width spans 0.07–0.10 feet [0.02–0.03 metres]. The joints break away with ease. Small, round areoles crowd each joint, reaching down to its base. Each joint has 30–60 areoles, sometimes more.

Most areoles bear spines, with four to fifteen in each cluster. Spines reach about 0.13 feet [0.04 metres] long. Their bases are white, with dark upper parts or black tips. As stems age, the spines fade to a dull grey. Most spines are thin, though some are stout. They spread and interlock, pointing upward or down. Large flowers blend pink and white. The pericarpel, which surrounds the ovary, bears bristles near its top. Red fruits are dry, with thin walls and narrow bases. They reach about 0.07 feet [0.02 metres] long. Fruits lack spines, but fine white bristles project above them. The seeds are white.

In cultivation, give this cactus sun and a mineral potting mix. The mix must drain well to limit damage from excess water. Its long, thick taproot needs a deep pot. Shield plants from fierce summer sun and excess heat. Water during active growth, but avoid keeping the roots too wet. Keep plants dry during winter rest to help prevent rot. A cool winter rest supports health and flower bud formation. Plants also need good airflow. LLIFLE reports frost tolerance near −5°C, with −10°C as a lower extreme.

The cushion shape and large flowers suit a potted cactus collection. Propagation from rooted cuttings is more reliable than sowing seeds. Seeds can be very hard to germinate. Growers also use grafting to speed growth and preserve spare plants. The supplied sources give no evidence of edible or medicinal uses. They do not establish safety for people or pets.