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The Giving Garden – Rethinking the food-medicine continuum in the urban sprawl

nov 25, 2024

Crop of the month: Lowveld Chestnuts

The Lowveld chestnut (Sterculia murex) is a peculiar tree species found growing in the cracks of granite inselbergs in the Mpumalanga Lowveld, Kruger National Park and eSwatini. The species, known as ‘umbhaba’ in isiSwati and ‘mohlatsane’ in sePedi, is easily identified from its palmate leaves, distinctive waxy, yellow, petalless flowers, and large, spiky, charismatic fruits. The seeds are large, oily and edible with a sweet taste and have, in our opinion, great potential as a food plant in edible landscapes in the warmer parts of South Africa as they are easy to grow and produce high yields.

 

Blossoms of Sterculia murex appear in huge numbers in spring. Photo by Jason Sampson

Trees can be incredibly heavy-bearing and rapidly shed their fruit in February and March to coincide with the heavy rains in their habitat. The nuts are delicious both raw and cooked in a similar fashion to the ‘true’ chestnut, and the soft, leathery shells will “pop” slightly when roasted in a pan or over the coals of a fire exposing the edible flesh of the seed. According to the 2017 study by Regnier et. al., the nuts contain 14% protein with a high percentage of glutamic acid, aspartic acid, arginine, leucine and glycine, and 16% oil. Regnier et.al. (2017) also found the nuts to be a good source of selenium, copper, calcium and iron, and possess phenolics with a good antioxidant activity. The study recommends roasted lowveld chestnuts as a potential  ingredient for breakfast cereals, energy bars, and snack mixes to boost the nutritional value of these products. At our collaborative Indigenous and Orphan Crops Dinner held at the University of Pretoria’s Future Africa campus in June 2024, the lowveld chestnuts were incorporated into a bread along with water chestnuts (Eleocharis dulcis) and the recipe will be available in the December issue of Veld & Flora

 

Opened pods with nuts. Photos by Richard Hay

 Humans aren’t the only species to take advantage of the nutritional value of lowveld chestnuts – the nuts are heavily predated by a wide range of animals meaning they will need to be harvested as soon as they start falling. From our experience, it’s best to harvest the nuts as soon as the pods open on the trees. This can be done by knocking the pods with a long pole or shooting the pods down with a slingshot. The inside of the fruits bears small hairs which may cause irritation to the skin, and so care should be taken when harvesting to avoid these.

The species is generally common in its habitat, albeit range-restricted, yet despite being very easy to grow in frost-free spaces it is still relatively uncommon in cultivation. Trees can become large, reaching heights of approximately 12m, but in their early years are fairly slender without much spread to the crown. The roots are large and fleshy, and can be damaging to paving and foundations, so care should be taken when identifying a suitable place to plant. Seeds should be planted as fresh as possible as they cannot withstand drying out. In climates with a lower humidity than the species’ natural range, such as here at the University of Pretoria, this means collecting and planting the seeds as soon as the pods open. We have managed to delay germination by close to a month by placing fresh seeds in sealed plastic bags and storing them at 10°C, however, the seed quality declines rapidly if they are stored any longer than this.

 

Harvesting freshly-opened pods at the University of Pretoria’s Hatfield campus.

Photo by Kayleigh Murray

Germination is rapid, but the species has evolved a peculiar survival strategy by putting down a large caudex deep into the soil as soon as they germinate. This allows the plant to survive hot, dry winters before putting out its first leaves in the spring following germination.This means you won’t see any growing activity on the surface for seven months after planting. We have found that large numbers of seeds can be sown in closer proximity in seedling trays, and the resulting caudexes dug up and split over winter and planted out into individual pots and bag, or straight into the ground, in time for their spring flush. Seeds are susceptible to bacterial rot, and treating seeds with a bactericide such as copper oxychloride will reduce the risk of rot. Caudexes should be kept dry in soil over their first winter, as they can be susceptible to rot if watered during this dormant period.

Lowveld chestnuts have great potential and we’d highly recommend them as an addition to any edible landscape project. If you have any questions about the species, please don’t hesitate to reach out to us at the Manie van der Schijff Botanical Garden.

 

 

BotSoc Conservation Project Coordinator, Northern Region

richard.hay@up.ac.za or north@botanicalsociety.org.za

 

Jason Sampson

Head Curator: Manie van der Schijff Botanical Garden, University of Pretoria

jason.sampson@up.ac.za

References:

Regnier, T., Kazaz, S., Du Plessis, B., De Jager, K., Augustyn, W., Roux-Van der Merwe, R. and Badenhorst, J., 2017. Quality and safety of Sterculia murex, a scientifically unknown nut from Southern Africa. South African Journal of Botany, 108, pp.287-293.

 

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The National BotSoc office will be closed on Friday 6 December 2024.


The National BotSoc office will close for the festive break from 12:00 (midday) on 24 December 2024 to 3 January 2025, and reopen 6 January 2025.

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