The Phyto-Philes: Rock Sage
Created | Updated Apr 26, 2015
Rock Sage
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
For this installment I introduce you to a plant that is not at all widely known but very deserving: the Rock Sage, Thorncroftia succulenta. Its genus name honours George Thorncroft, a botanical collector of the nineteenth to early twentieth Century who is credited with many wonderful plant discoveries. The species name signifies that this sage is succulent. The genus Thorncroftia contains four more species, all of them growing in South Africa.
Succulent Sage of the Rocks
This rock sage grows in the wild in my province, Limpopo, as well as our neighbour province of Mpumalanga. Its habitat is typically rocky, such as mountain slopes or the small hills called 'koppies' ('little heads'). They often grow in shallow pockets of soil and leaf litter, that collect in cracks between rocks or in hollows on top of rock sheets. The plants mostly grow as spreading, many-branched shrubs. Their stems are succulent at first; older stems become more woody. The leaves, too, are succulent, and covered by short, velvety hairs. Like most members of the sage family, they are aromatic. When I encounter sages in the wild, I enjoy rubbing the leaves between my fingers to get a sense of their scent. The aroma comes from compounds in the leaves that probably have some protective function; not many insects enjoy eating these pungent plants.
The succulent nature of these plants aids their survival. The shallow soil in rocky regions can't hold much water. During the long, dry autumn and winter, these substrates can dry out completely. But the rock sage stores water in the cells of its succulent leaves and stems. These sustain it over the winter until the rains start again in spring. The light colour of the stems and the velvety hairs of the leaves also protect them against the harsh sun and decreases the rate at which water evaporates from them.
While rock sage shrubs are quite attractive for their velvety, succulent leaves, they are at their prettiest when in flower. The flowers can cover the shrubs in good seasons, but are beautiful in themselves. They are very delicate, and pinkish-purple, marked with darker spots on the petals. The lower parts of the petals form a long, thin tube containing the nectar. The flowers are pollinated by insects, probably butterflies and/or moths.
The Succulent Sages of South Africa
This is actually by far not the only succulent sage species in South Africa. Not many people are aware of these as succulents; most growers think of the prominent succulent groups like the aloes, , euphorbias,, mesembs, crassulas or carrion flowers when they think of South African succulents, but we have succulents in many other groups also, and the sages are by far not the least of these. About forty local species in the sage family are noted for succulence. Like other succulents they display a great diversity of forms. Some like Plectranthus ernstii have stems that become very fat, like miniature baobab trees, while others have fat leaves with a variety of shapes. Some like Plectranthus oertendahlii have beautifully mottled leaves. Most of them have very pretty flowers, and then there's their wonderful aromatic scents as well. They vary from small herbs to Tetradenia riparia which can become a fair-sized tree. Some are annuals or very short-lived, while others can live to a ripe old age. Some grow in desert regions, while others grow in the shady leaf-litter of coastal and riverine forests. All in all, they are a wonderfully diverse and fascinating group.
Even the non-succulent sages of South Africa are fascinating – and we have a great diversity of those also. Some of them probably have potential as culinary herbs, or as ingredients for perfumes, but mainly they are pretty and interesting plants to encounter in the wild. My own region, Limpopo, happens to be a centre for diversity of these plants, and I've encountered a variety of them on my excursions. Many of these have great potential as garden plants, grown for their fragrant foliage and their exquisite flowers. Most of them are hardy and not fussy, quite easy to grow.
Growing the Rock Sage
The rock sage is an excellent plant to grow. It is quite hardy, able to endure a long winter drought, and even moderate frost! It can also grow on infrequent rain over the spring and summer. It becomes a neat, rounded to spreading shrub, at most 1.5 m/5' tall. It retains its leaves year-round and has a fresh, vigorous appearance. Then there are its lovely flowers, which remain on the shrubs from the summer into the autumn and sometimes even into the winter!
Because of its soft, succulent stems, this species can be easily shaped and grown as a quirky succulent specimen or as a bonsai. I would suggest that it not be kept too small, but rather be given a large pot or tray and allowed to grow and branch and spread. Simulating its natural growth situation, with a little bit of soil and a rock or two, would in my opinion produce the most impressive results.
As for how to grow it, that is quite easy! The most convenient way to propagate the rock sage is by cuttings. These can be small or large, but must be left for a day or few to form scab tissue over the wounds where they were cut. They root easily in spring or summer and need no special treatment – just stick them in the growing medium (which should be well-draining with a good proportion of sand as well as a bit of compost) and keep them on the dry side of moist.
This species can also easily be grown from seed. Collect these from the capsules at the end of winter. They are small, black and numerous. Mix the seeds with sand, and then sprinkle this sand/seed mix over the top of the growing medium. Do this at the start of spring, so the little plants can enjoy a full growing season. Keep them moist and they should soon germinate and grow vigorously!
Rock sages do best in regions with hot summers and dry winters. They won't tolerate very wet conditions. They enjoy being planted between rocks, in full sun. They can grow in light shade too. In regions that are too wet and cold, they can be grown in hothouses, or in clay pots on sunny windowsills or porches. The rock sage is an easy and rewarding plant to grow.
