Lithops

Lithops is a genus of succulent plants in the family Aizoaceae, native to the arid stony plains and rocky outcrops of southern Africa, primarily South Africa and Namibia. Their remarkable resemblance to pebbles provides camouflage against herbivores, earning them the common names 'living stones' and 'pebble plants'. Each plant consists of a pair of highly succulent, fused leaves separated by a central fissure, from which solitary daisy-like flowers emerge in autumn. Mature plants measure only 2–5 cm across and grow extremely slowly. Culture demands exceptionally fast-draining mineral substrate, maximum sunlight, and a strict seasonal watering regimen: minimal water from autumn through spring, complete drought in summer. Incorrect watering during the shedding cycle can cause the old leaf pair to fail to dry properly. Their unique appearance and challenging cultivation make them prized specimens among specialist collectors.

Source: Wikipedia (CC BY-SA 4.0)

Water: 1-2x monthly fall-spring / completely withhold in summer and during shedding