Ariocarpus trigonus

Ariocarpus trigonus is a cactus from northeastern Mexico. Its native range covers Tamaulipas and Nuevo León. It belongs to the cactus family, Cactaceae. Kew places it in desert or dry shrubland. LLIFLE records it on limestone, where large colonies can form. These sites lie at 1,970–3,940 feet [600–1,200 metres] above sea level. Its recorded habitat extends more than 1,310,000 feet [400,000 metres]. English names include living rock and star rock.

The plant forms a single rosette close to the ground. Much of its body stays below the surface. A taproot anchors the plant beneath its low stem. The stem has a round top and a somewhat flattened shape. Its colour is most often yellow-green. LLIFLE gives a height range of 0.13–0.82 feet [0.04–0.25 metres]. Stem width ranges from 0.16–0.98 feet [0.05–0.30 metres]. The source does not separate garden sizes from wild measurements.

Long, pointed tubercles give the rosette its leaf-like outline. These fleshy growths spread apart rather than crowd together. Their upper faces are smooth, flat, and free of cracks. Each tip bends inward, though the growths stand upright. Colours range from yellowish tones to brownish grey. Tubercles measure 0.10–0.26 feet [0.03–0.08 metres] long. Some are long and narrow; others are short and broad. The small areoles sit near their bases. Only very small plants have spine-bearing areas at the tubercle tips.

Flowers open in late autumn or early winter. They range from cream through pale yellow to yellow. Some have red lines along the petal centres. The petals have a soft sheen. Each bloom spans 0.10–0.16 feet [0.03–0.05 metres]. Flowers can reach 0.13 feet [0.04 metres] in length. The fruit is whitish or greenish. It measures 0.023–0.066 feet [0.007–0.020 metres] long. Its width is 0.016–0.033 feet [0.005–0.010 metres].

Sources differ in how they name this plant. RHS lists Ariocarpus trigonus and gives Ariocarpus elongatus as a synonym. LLIFLE treats it as Ariocarpus retusus subspecies trigonus. Its species page still describes the plant under the requested name. The supplied species-level evidence gives no firm cultivation or frost guidance. It also gives no supported account of pests or disease. Food use and safety remain unconfirmed by these sources.