Leuchtenbergia principis aka Agave Cactus

Leuchtenbergia principis is a cactus known as agave cactus. Other names include cob cactus and prism cactus. It is the sole species in its genus. Its native range lies in Mexico, reaching Jalisco. It grows in desert and dry shrubland. Wild plants also grow in semi-desert on lime-rich soil. They occur at elevations of 4,921–6,562 feet [1,500–2,000 metres]. Plants grow scattered across a broad area, often among agaves or Hechtia.

This slow-growing succulent can reach 2.3 feet [0.7 metres] tall. It grows alone or forms offsets over time. A large, swollen taproot lies below the stem. The stem is round and becomes bare at its base. With age, that base forms a short, corky trunk. The trunk can reach about 0.25 feet [0.075 metres] thick. These changes give older plants a form unlike young ones.

Long tubercles give this cactus its agave-like shape. These are stem growths rather than true leaves. Each has a triangular cross-section and a blunt-looking tip. Their colour ranges from grey-green to blue-green. Purple-red patches can mark their tips. Tubercles measure about 0.2–0.5 feet [0.06–0.15 metres] long. Older ones near the base dry and drop off. Wool grows in the axils and at the tip areoles. Flexible, papery spines grow from these areoles. Central spines can exceed 0.66 feet [0.2 metres] long.

Mature plants bear large yellow flowers with a scent. Plants must reach at least four to five years old. The funnel-shaped blooms arise at the tips of new tubercles. Each flower spans about 0.16–0.33 feet [0.05–0.1 metres]. Blooming comes in separate flushes from spring through autumn. The smooth fruit ranges from green to violet. It can have a dull, waxy coating. Each fruit measures about 0.1 feet [0.03 metres] long. Its base opens at ripeness, releasing several hundred large seeds.

Its unusual shape gives it interest as a specimen cactus. The supplied species account does not establish a cultivation regime. It also gives no firm hardiness limit or safety rating. Wild plants face pressure from illegal collecting and livestock grazing. Mexico lists the species as threatened under its national protection system. That national listing does not establish an IUCN category.