Sterculia (2019)

By Bob Williams (November 2019)

At our October 2019 meeting, Pam Schnebelen brought in a bonsai tree on which the leaves were starting to turn colors. Dormancy was just around the corner. It was an interesting plant and one with which I was not familiar. This plant is not a true succulent, but makes an interesting bonsai specimen. The plant she displayed was Sterculia africana.

Sterculia is a genus of plants in the mallow family, Malvaceae and the subfamily Sterculioideae. Members of the genus are sometimes called “tropical chestnuts” due to the size of the seeds. Some species have the nickname of “false baobab” because small trees resemble baobab trees. Species within Sterculia consist of evergreen or deciduous shrubs and trees. The genus gets its name from the Roman god Sterculius, the god of manure.

The flowers produce an aroma that rivals members of the Stapeliad family. According to KewScience, there are 177 recognized species native to tropical and temperate areas of Asia, Africa, South America, Central America, Australia and North America (Florida).

One of the characteristics of the species in this genus is that the leaves and fruits have fine hairs on them. These hairs can cause irritation and discourage animals from eating the sterculias. The plants can grow up to 50 feet in height and can be found in a wide variety of soils – from rich or gravelly to rocky outcroppings.

Sterculias are valuable in the wild, for there are many medicinal uses for them. Gum karaya extracted from Sterculia species is used as a laxative and a denture adhesive. In some areas, the leaves and bark are boiled, and the steam is inhaled to treat fever and influenza. In Tanzania, the roots are boiled and taken as an aphrodisiac or to treat back pain, hernias, dizziness, fungal infections and convulsions.

In Namibia, a root or bark drink is used by women for the treatment of stomach pains. A leaf tea is drunk for treating cough and chest pains. A fruit tea is drunk to relieve pain during pregnancy and after giving birth. In Malawi, the hairs of the fruits are burned, and the ash is used in an ointment for the treatment of eye infections, especially in babies.

Sterculia plants are used in other ways, as well. Oils from the fruits are extracted for cooking. The gum karaya is used as a thickening agent. The seeds are dried, ground and used as flour. Roasted seeds are eaten by humans, while raw seeds are used to feed cattle.

The bark is made into rope and twine, and used to construct mats and baskets. The bark is also used to create beehives. Some of the taller species are harvested for lumber.

The plant Pam brought in, S. africana, is a common tree in Africa. It is found from Socotra down through tropical Africa to Namibia. It grows in lowland areas in rocks or on gravel plains. These plants grow in open areas with lots of sun that receive some rainfall. Under good conditions in the wild, this sterculia will grow 30 to 45 feet tall and can have a diameter of up to 3 feet. When growing in rocky areas, they tend to form a natural bonsai.

One of the appealing characteristics of S. africana is the bark. It has a peeling, paperlike appearance that can be in reddish in color. The aromatic flowers are greenish-yellow with red stripes. In my research, I could not find a temperature range for the plants. However, they are not winter-hardy in our area and lose their leaves during the winter dormancy period.

Sterculias are plants for bonsai enthusiasts. The plants can be started by cuttings or, more commonly, by seed. If the seeds are fresh and correctly stored, the germination rate can be between 65 and 90 percent. Seedlings should show themselves in two weeks and quickly start to develop a large, deep taproot. If starting from seed, decide on the bonsai pot somewhat quickly – one source said by the third year of growth.

Although these plants are not commonly sold, seeds are typically found for sale. For the bonsai person in our hobby, these plants provide something out of the ordinary.

Sources:
KewScience Plants of the World Online – http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:329918-2
KewScience Plants of the World Online – http://www.plantsoftheworldonline.org/taxon/urn:lsid:ipni.org:names:825091-1
Famine Food Field Guide – http://www.africa.upenn.edu/faminefood/category1/cat1_Sterculia_africana_ok.htm
Pl@ntUse – https://uses.plantnet-project.org/en/Sterculia_africana_(PROTA)
Hindawi – Antibacterial Potential of Extracts of Sterculia africana, Acacia sieberiana and Cassia abbreviata… – https://www.hindawi.com/journals/ijz/2018/9407962/
JSTOR – https://plants.jstor.org/compilation/Sterculia.africana
Wikipedia – https://en.wikipedia.org/wiki/Gum_karaya
Useful Tropical Plants – http://tropical.theferns.info/viewtropical.php?id=Sterculia+africana