| Summer and Winter in southern Africa : Cotyledon and Tylecodon (part 1)
Rain in the eastern part of South Africa generally falls in summer; in the western part of the country it rains in winter. This simple statement contains the key to the successful cultivation of many South African succulent plants. As with many simple statements of fact, however, the reality’s a little more complex. Mountain ranges create rain shadows that turn what otherwise would be a wet season into one of consistent drought. Coastal proximity may bring more rain, or it may bring seasonal fog.
The winter rainfall region begins part way up the coast of Namibia and makes a rough curve, extending farther east as it stretches farther south. Many of the areas directly east of its irregular boundary aren’t really in the summer rainfall area either. These include places very rich in succulent plants. For example, the semi-arid Little Karoo, may receive a bit of rain anytime in the year. On the whole, summers and winters tend to be drier than spring and fall, but in some parts the rains may fall mostly in summer and winter.
Just to the north, behind the Groot Swarteberg mountains, in the Great Karoo the sparse rains fall in late summer and autumn. Other South African transition zones such as Bushmanland and the Tanqua Karoo, rarely receive rain at all, but, once again, occasional storms may come any time of year, most likely winter in the west, summer in the eastern parts.
The northwest-most parts of South Africa , Namaqualand and the Richtersveld, receive as much moisture from fog as from the winter rains. Across the border in Namibia, the strictly winter rainfall area narrows and clings closer to the coastal regions as it moves northward; east lies a parallel band where rain may fall anytime of the year (or not at all), farther east the rainy season comes in summer. About halfway up the coast the summer rain area touches the ocean, but for a long ways to the north the fog keeps more things alive than the extremely unreliable rain.
Understandably, plants with broad geographic ranges tend to be adaptable to a variety of rainfall patterns, while plants from small and localized habitats are often quite demanding in their watering needs. On the whole, plants from summer rainfall regions behave more normally, those of the winter rainfall areas not only act oddly in cultivation, they also comprise some of the strangest looking and most fascinating of succulent plants.
Now split in two, the formerly united genera of Cotyledon and Tylecodon embody the contrast between summer rain and winter rain plants.
Cotyledon
Two genera, Cotyledon and Tylecodon, exemplify the nature of these environmentally determined horticultural requirements. The two genera, along with Adromischus, make up a related subgroup of African succulent plants in the Crassula family. Cotyledon, the earliest named of the three, dates from the 18 th century, when succulent plants were being introduced to the emerging world of European natural science. Over the decades, Cotyledon became a sort of catch-all designation for a great number of crassulaceous plants, including species from the New World (Dudleya, for example) as well as the Old. As taxonomic boundaries gradually clarified, one group of plants after another was split out of the genus (Adromischus was removed in the 1830s). Finally, in 1978, in its latest revision, the botanist H. R. Toelken combined many species of Cotyledon formerly considered distinct and devised a new name, Tylecodon (an anagram of Cotyledon), for the new genus he’d created for species that didn’t fit in with his revised concept of Cotyledon.
Pruned down to fewer than a dozen species, Cotyledon currently consists of small to medium sized shrubs and bushes with perennial, thickened succulent leaves and upright inflorescences that bear red to yellow, generally pendent, fleshy flowers. The genus ranges across much of southern Africa , in both winter and summer rainfall areas and encompasses the much smaller range of Tylecodon within its boundaries. Outlying species of Cotyledon extend into southern Angola in the west, and in the east, grow as far north as Ethiopia and southern Arabia . Regardless of their native habitat, however, cotyledons are universally easy to grow and will respond to the same conditions. As cultivated plants, the larger forms and species make good specimens for rock gardens while the smaller ones can flourish for many years and under a variety of situations in containers.
Cotyledon orbiculata , by far the most common cotyledon in cultivation, in nature grows over much of southern Africa and takes on a bewildering number of forms. At various times many of these forms were considered separate species, but the differences, mostly in details of leaf size and flower color, didn’t justify such a significant demarcation. C. orbiculata’s plethora of forms include plants with linear, nearly terete leaves arranged in loose rosettes, or with thick, elongated egg-shaped leaves (C. orbiculata fm. oophylla), while the slow-growing form undulata has white, waxy leaves with an undulating edge, almost like graceful, chalk-colored seaweed.
The most frequently grown types of C. orbiculata, however, resemble a slower growing, white or gray leafed version of the common jade plant, Crassula portulacea. These typical forms have a stocky main stem and put out their succulent branches quite freely, ultimately reaching around two feet in height and more than that in width. Aside from their pendent, bell-shaped pink flowers, their most striking feature is the white or even silvery waxy coating that covers their thick, spoon-shaped leaves. Other forms of C. orbiculata lack this glaucous coating. In a fairly well watered part of the Little Karoo I saw some of these all green forms with leaves as much as four inches across while the plants themselves were over four feet tall. In good light the leaves, glaucous or not, develop a red edge.
A second, distinctly different group of species, plants with green, densely hairy leaves and thinner, less succulent stems, includes the slow growing, yellow-flowered C. campanulata, and the more shrubby (but still fairly small) C. tomentosa and its variety, ladismithiensis, with yellow to orange flowers and wedge shaped leaves with little notched teeth at the tips. The remaining cotyledons, small to fairly large shrubs, have glabrous (non-fuzzy) leaves and include C. papillosum, a small, low-growing, densely branching plant with wedge-shaped, rather squared-off looking leaves, which grows over the west of South Africa and into its central regions, as well. C. cuneata, also fairly small, with green, red-edged, spoon shaped leaves, which inhabits only the winter rainfall regions of Namaqualand and southern Namibia , in the west. Though C. woodii, a sprawling, rather nondescript shrub, gets larger, its waxy, oval, almost coin-shaped leaves don’t reach more than an inch across. Finally, C. barbeyi, a quite variable, good sized plant with loosely arranged, spoon-shaped leaves, grows from the eastern part of South Africa up the east side of the continent as far as Ethiopia, and then across the Gulf of Aden into Arabia.
None of the cotyledons commonly in cultivation presents any problems when it comes to care. Given good drainage the larger forms of C. orbiculata will thrive outdoors in areas of relatively mild climate, such as most of coastal California . They adapt well to winter rain and will tolerate several degrees of frost in a rock garden. The smaller species and forms will do fine in a sunny spot in or out of doors if protected from extremes of rain and weather. Not fussy about soil, cotyledons will be happy with any standard, well drained succulent mix. Propagation from stem cuttings (particularly with the thicker stemmed forms) is easy, from leaf cuttings considerably more difficult. Regardless of whether they come from summer or winter rainfalls areas in the wild, all the cotyledons will do well with regular watering in the warmer months (about once a week in a fairly sunny, warm climate), and less water (perhaps every three weeks or so) in winter. C. orbiculata does almost too well in southern California , where it has escaped cultivation in some locations to naturalize near the coast.
The Garden has a decent selection of cotyledons, and we have some from time to time to sell. Though not the most spectacular of succulents, their general hardiness ensures the value of cotyledons in mixed plantings of xerophytic plants, and some of the more attractive forms and unusual species can become small showpieces in their own right.
Next month, just as we come to the end of their growing season, we’ll continue with this group of plants and discuss some of the more spectacular and just plain weird members of the genus Tylecodon.
|
