Black leaf markings tend to proliferate on old Cerochlamys pachyphylla leaves as seen here. Similar black markings are found on the leaves of many other Little Karoo succulents. While various fungi grow on plant leaves and damage the plants, lichen doesn’t damage host plants.
These markings are thought to be lichen and although unsightly will not kill the plant. Might photosynthesis in the host plant be impaired, however, in favour of photosynthesis within the lichen?