While both Lithops and Split Rocks are mesmerizing mesembs (members of the Aizoaceae family) from South Africa, they belong to different genera. This is the most crucial botanical distinction. Lithops are all species within the genus Lithops, which contains dozens of species and cultivars. Split Rocks, however, refer primarily to a specific species, Pleiospilos nelii, within the genus Pleiospilos. Some may also use the term for its relatives like Pleiospilos bolusii. Understanding they are from different genera explains why their care, particularly regarding water, differs significantly.
The most noticeable difference for enthusiasts is the number of leaf pairs, or "heads," present at one time. A Lithops plant consists of a single, fused pair of leaves that form one head. It will only ever produce one set of leaves at a time. The plant's entire lifecycle happens within this pair: it grows a new leaf pair from the meristem in the center, which draws moisture and nutrients from the old outer leaves, which then shrivel away.
In contrast, a Split Rock (Pleiospilos nelii) can often have two, three, or even four pairs of leaves simultaneously. It produces new leaves from the center, but the old leaves may persist for a long time as the plant matures, creating a stacked or clustered appearance. This is a key visual identifier; if you see multiple leaf pairs, you are almost certainly looking at a Split Rock and not a Lithops.
Both plants produce large, daisy-like flowers, but their origin point is a reliable differentiator. A Lithops flower will almost always emerge from the fissure between the two leaves of its single head. The flower bud pushes its way through the narrow slit where the leaves meet.
A Split Rock flower, however, emerges from the center of the plant, the same place from which new leaves grow. Because a mature Pleiospilos nelii can have multiple heads, you may see a flower stem rising from the central point between several leaf pairs, rather than from a single, specific slit.
This is the most critical care difference stemming from their physical structures. Lithops have an extremely conservative growth cycle. They should only be watered during specific periods: in the fall after flowering and as the new leaves are developing in spring. Water is completely withheld when they are dormant in summer and during the winter after the old leaves have fully dried up. Watering at the wrong time can cause fatal rot.
Split Rocks are slightly more forgiving but still drought-tolerant. Their ability to sustain multiple leaf pairs means they have a larger internal water reservoir and a slightly higher water requirement than Lithops. However, the golden rule is to water only when the innermost set of leaves begins to feel slightly soft or wrinkled. The presence of multiple leaf pairs often tempts owners to water too frequently, which leads to rot. A stacked Split Rock is a sign of overwatering, not health.
