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Plant Highlight: Cheiridopsis purpurea
by Brian Kemble
About the family and genus
The Ice Plant Family, Aizoaceae, is a large one, with many genera and about 1,800 species, many of them highly succulent. The family is not exclusively native to southern Africa, but the great majority of the species occur there, where they may be found both in the summer-rainfall region and in the winter-rainfall region. Among the genera concentrated in the winter-rainfall zone is Cheiridopsis. Plants in this genus have showy flowers that often appear in winter, with fleshy leaves that range from long and finger-like to short and globular. In between are species with leaves like stubby thumbs, and among these is Cheiridopsis purpurea, from the Richtersveld in the arid northwest corner of South Africa.
About the plant
As is typical of plants in its genus, Cheiridopsis purpurea forms compact multi-headed clumps, with each head producing a pair of leaves each year when the growing season begins in the fall. New heads are added over time, so that older specimens become substantial clusters of many heads. The plants grow and flower during the winter months, then shrivel and go into their resting mode during the dry summer months. When the next fall arrives, a new pair of leaves emerges from between the previous ones, and at right angles to their predecessors. Leaves in the genus range from long and nearly cylindrical to short and globular, and C. purpurea is somewhere in the middle, with its leaves looking like pale milky blue-green thumbs. The leaf length is 1.2 to 2 inches (3 to 5 cm), with the lower portion of the leaf fused with the other one in its pair. The upper side of the leaf is flattened, with the lower side bulging and having a distinct keel. Sometimes there are small teeth along the leaf margins or on the keel, but these are not prominent and are not always present. Up close, it can be seen that there are tiny translucent dots peppering the leaves, these being darker than the surrounding leaf surface.
About the flowers
The flowers emerge in winter, but the timing varies from year to year. At the Ruth Bancroft Garden in Walnut Creek, California, our plants have started as early as late November, and as late as mid-February. Of course, in its Southern Hemisphere home, winter comes at the opposite time of the year. A flower begins as a shoot coming out of the slit between the two leaves in a leaf pair, with fleshy bracteoles* clasping the pedicel, these looking like smaller versions of the leaves. The bases of the uppermost bracteoles surround the bud, which opens into a purple or magenta-purple flower with a diameter of about 1.38 inches (35 mm). As is common in the family, the flowers stay closed until the middle of the day, and after putting on their afternoon show they close up again before evening arrives. The vivid color of the flowers contrasts dramatically with the pallid leaves.
About the fruits and seeds
After pollination, the stamens and petals wither and are shed, while the ovary at the flower’s base swells to become a fruit with a bowl-like base. As the bracteoles around the perimeter of the fruit dry and wither, they form a ragged rim surrounding the flattened top. The top has 10 radiating slits showing the locations of the 10 locules, or seed chambers within. Though 10 is the usual number of locules, the count can vary a bit. After a rain, the moisture causes the capsules (the dried fruits) to swell and open up, with the ten “pie-wedges” between the locules pivoting outward to expose the interior of the capsule (and the seeds within the locules). The tiny brown seeds are splashed out when the capsule is struck by raindrops, but not all of them are dislodged. When the rain ends and the capsule once again dries, it closes back up, waiting for another rain event to repeat the process. Open capsules look like intricately carved wooden flowers, dramatically different from the “closed fist” of the capsule when it is not open.
Plants in cultivation
Cheiridopsis purpurea is not well suited for growing in gardens outside of areas with a Mediterranean climate, since it dislikes summer humidity as well as temperatures that drop very much below freezing in winter. In other climate zones, it can be grown as a potted plant in a greenhouse. In habitat, it gets only about 4 inches of rain per year (100 mm) during the winter months, followed by long dry summers. At the Ruth Bancroft Garden in Walnut Creek, California, our average annual precipitation is a good deal more than this (a little over 20 inches, or 500 mm), but plants grown on mounds with sharp drainage can handle this if given a sunny position. It is especially important to be sure that the placement allows the plant to get direct sun in the afternoon in winter, to encourage its flowers.
*A bract is a modified leaf occurring at the base of an inflorescence, or on the stalk of an inflorescence (peduncle), while a bracteole is a smaller modified leaf occurring on the stalk of an individual flower (pedicel).
