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Plant Highlight: Crassula rupestris

November 2023

Family and region

The Crassulaceae, or Stonecrop Family, is a prominent group of succulent plants, with many genera and species found in various parts the world. The family takes its name from the genus Crassula, named by the botanist Linnaeus back in 1753. This genus contains about 194 species (Gordon Rowley: Crassula, A Grower’s Guide, 2003), and although these occur around the world, they are especially abundant in southern Africa, home to about 150 species. On the whole, they are small plants, although one of the best known is also one of the largest: the jade tree, Crassula ovata. While the jade tree has a shrubby growth habit, other Crassula species form small rosettes or tufts of leaves, and a few develop long trailing stems. One of the latter is Crassula rupestris, occurring widely in the southern and southwestern part of South Africa.


About the plant

Crassula rupestris is a clump-forming plant, found on rocky slopes and on cliffs. It often grows as a dome of many stems, the central ones erect and the peripheral ones sprawling to the side, but in steep locations it may spill downward as the stems elongate. The slender stems are initially supple and about .08 inch in diameter (2 mm), but they later become woody and attain a diameter of up to .2 inch (5 mm), with a length of up to 20 inches (50 cm), though often less than this. At regular intervals along the stem are pairs of opposite leaves, fused at their bases so that the stem appears to pierce them. In this respect, Crassula rupestris resembles Crassula perforata, but the latter has somewhat longer stems with larger and more triangular leaves. Florally, the two species differ in that C. rupestris has shorter and wider clusters of white to pink flowers in the fall, while C. perforata has more elongated inflorescences with cream to yellowish flowers in the spring.

The chubby leaves of C. rupestris are oval in shape with blunt tips, usually .4 to .6 inch long (10 – 15 mm) and .31 to .48 inch wide (8 to 12 mm). However, this is a variable species, and populations with leaves smaller or larger than this are known. The basic leaf color is light green, gray-green or milky blue-green, with yellowed or reddened margins, but under dry conditions and in exposed locations plants may become quite red. The spacing of the leaf pairs along the stem is variable, but generally the spacing is close in sunny positions, and farther apart with less direct sun.

In cultivation, the cultivar ‘Tom Thumb’ is often seen, sometimes labeled as Crassula rupestris ‘Tom Thumb’, or sometimes simply as Crassula ‘Tom Thumb’. This is a small-growing selection of Crassula rupestris with white flowers.


About the flowers and fruits

Crassula rupestris is a fall-flowering species, though flowers at other times of the year are also possible. The inflorescence is an extension of the stem on which it is poduced, branching and re-branching so that multple small clusters of flowers are crowded together in a domed or flat-topped group atop the stem. The white or light pink flowers are cupped at the base, with the five petals curled back to expose the five carpels at the center, each tipped with a sticky stigma for receiving pollen, surrounded by the five stamens with their dark brown pollen-bearing anthers. These are small flowers, with the petals only only about .16 inch long (4 mm). As with other plants in the Crassulaceae, the carpels mature into seed-bearing follicles that split open when they dry to release the many minute seeds.


Care and maintenance

If provided with good drainage and sufficient light, C. rupestris is easy to grow, performing well in pots or in dish gardens as well as in the ground. In nature, it grows in winter-rainfall areas as well as in places with year-round rainfall, so it it does not require a dormant period. It can easily cope with brief dips below freezing in winter, but sustained freezes should be avoided.


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