With attractive flowers, heady scent, glossy leaves and unusual fruit, it is perhaps surprising that the wild gardenia is not more commonly used as a garden staple. It also makes a good container plant and it does well as a flowering bonsai plant.
The wild gardenia (Gardenia thunbergia), also known as the forest, starry or white gardenia, flowers in the months of summer, when the plant carries its creamy blooms in various stages of maturity.
In the wild it is a forest plant, growing in or on the margins of coastal and inland forests in the eastern regions of southern Africa, from the Eastern Cape and north into Mozambique. It is a slow-growing plant that thrives in sun or dappled shade, eventually reaching a height of 5–7 metres.
I like how the plant with its dense foliage brings a foresty feeling to the garden. The scent of the flowers, especially at night, is exquisite and the flowers attract night-flying moths.
The genus Gardenia comprises about 60 species that occur in tropical and warmer parts of Africa, Asia and Europe. Of these, 6 species including Gardenia thunbergia are found in South Africa (but not in the Northern and Western Cape regions).
Gardenia thunbergia was one of the first South African gardenias collected by European botanists and it was introduced into the Royal Botanic Gardens at Kew in London as far back as 1773. Currently, it is still grown in the Palm House at Kew.
Several of the gardenia species, including Gardenia thunbergia, carry the isiZulu name umvalasangweni, which literally means the back-gate closer as gardenias were traditionally planted at homestead gates as a protection against evil spirits and gardenias were used to close cattle kraals.
The genus name Gardenia honours the appropriately named Dr Alexander Garden (1730–1791), a Scottish medical practitioner who settled in South Carolina in North America in 1752. He was a keen naturalist (botany and zoology) and collector, sending specimens to Linnaeus and other scientists in Europe (see more on Garden here).
The species part of the name, thunbergia, is named after the Swedish physician and botanist, Carl Pehr (Peter) Thunberg (1743–1828). He was a pupil of Carl Linnaeus at the University of Uppsala. His subsequent scientific work and collecting in South Africa and later in Japan led to him being called the “father of South African botany” and the “Japanese Linnaeus”. His many publications included comprehensive works on the flora of South Africa and of Japan. For more information on Thunberg see here.
The photo above shows how the petals are joined to a long tube, which is about 7 cm long. As the nectar is at the bottom of the tube, only large moths, such as hawk moths, which have a long proboscis, can reach down the long tube of the flower to reach the nectar.
The wild gardenia has rather stiff upright stems and it makes a good hedging plant. It is a prolific flowerer in the summer.
Gardenias are members of the Rubiaceae family (coffee family). In species in this family flowers are bisexual or unisexual. I think that the flower of the wild gardenia in the photo above is a male flower, as only the 8 pollen-producing anthers are present.
In this flower the stigma where the pollen germinates is visible in the centre of the flower, surrounded by the 8 anthers. Finding out a bit more about flower anatomy so as to better understand this wild gardenia flower, I read that the female part of the flower, the pistil, comprises the ovary in the swollen base of the flower, from which emerges the long style topped by the stigma (https://treesa.org/gardenia-thunbergia/). Any feedback from anyone who is better versed in flower anatomy than I am is very welcome.
As the flower ages the petals start to droop and turn beige in colour as they start to dry. The scent is still strong even as the flowers age.
This flower is almost completely shrivelled. As this is a female flower it will develop a fruit at its base. The fruits of the wild gardenia grow to be larger than a chicken egg and they are hard and woody.
The fruit swells from what was the base of the flower. Younger fruit is greenish with raised dots, but as it matures the skin becomes grey and very hard and woody.
A mature fruit of the wild gardenia, showing its rough grey skin covering with raised dots. In addition to being hard the fruits are very fibrous. The fruits do not self-seed and can remain on the bush for years without splitting. Propagation depends on the fruit being eaten by large herbivores such as elephants, large antelope and buffalo. Such animals eating the fruits act as seed dispersers.
In the absence of any assistance from large herbivores, gardeners and botanists have to work hard to harvest the seeds. The entry on Gardenia thunbergia on the SANBI website notes that secateurs are blunted in the process of cutting off the fruits, and that heavy blunt instruments such as hammers are required to break the fruits open. Most laboriously, nails or heavy-duty spoons are required to scrape and scoop out the seeds.
In addition to seeds, plants can also be propagated from cuttings and truncheons.
In traditional medicine parts of the plants including the roots and the leaves have been used for gastric complaints and skin diseases, for skin lesions resulting from leprosy and in the treatment of syphilis.
Being slow growing, the wood of the wild gardenia is dense and hard. The wood is a yellowish colour and takes well to polishing. Interestingly the wood can be bent without breaking. Because the size of the wood is limited, it has been used to make smaller items such as buttons, tools, clubs, yokes, axles and implement handles.
It is a dependable and easy plant to have in the garden. It retains its shape without needing pruning and it does not normally require watering, but drought conditions will test it. It prefers warmer climates and it is well suited to our part of the country.
Boon, Richard. 2010 (2nd ed.). Pooley’s Trees of Eastern South Africa. Durban: Flora & Fauna; Encylopedia.com. 2020. Alexander Garden. https://www.encyclopedia.com/people/science-and-technology/biology-biographies/alexander-garden; Notten, Alice. 2003. Gardenia thunbergia. PlantZAfrica. South African National Biodiversity Institute (SANBI). http://pza.sanbi.org/gardenia-thunbergia; Plug. C. (compiler). 2014. Thunberg, Dr Carl Pehr. S2A3 Biographical Database of Southern African Science. https://www.s2a3.org.za/bio/Biograph_final.php?serial=2843; Trees SA. 2020. Gardenia thunbergia. https://treesa.org/gardenia-thunbergia/
Posted by Carol