Research holds the key to more native spinach on our dinner plates

It’s known as native spinach, now researchers at Southern Cross University are trying to determine if Warrigal greens contain similar levels of oxalic acid as found in spinach and kale.

One of the main obstacles to Warrigal greens (Tetragonia tetragoniodes) being adopted as a mainstream vegetable - and a viable alternative to spinach - is the perceived high levels of oxalic acid in the leaves. In rare cases, too much oxalic acid can cause kidney stones.

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Lead researcher is Associate Professor Bronwyn Barkla from Southern Cross Plant Science. Professor Barkla is being assisted by chemist and Research Fellow Dr Ben Liu, also from Southern Cross Plant Science, and 2015 SCU Science Summer School student Carolyn Vlasveld, a Bachelor of Science graduate from Monash University.

“Oxalic acid is a naturally occurring chemical that is found in many different food sources such as leafy greens, nuts, seeds, most berries, certain fruits, soy and soy products, as well as meat and dairy products,” said Professor Barkla.

“High oxalic acid levels in food may constitute a risk to human health as these compounds readily bind calcium and other mineral nutrients to form oxalate crystals. This decreases the ability of the body to absorb these essential nutrients but also, the build-up of calcium oxalate crystals in the urinary tract is thought to lead to the formation of kidney stones.

“Studies have shown that soluble oxalate levels in T. tetragonioides can range from 1.5 per cent in leaves of older plants to 12 per cent in leaves of young plants.

“However, these levels are comparable to those reported in some varieties of spinach including those grown commercially. Yet people consume spinach on a daily basis.

“In this project we will grow both T. tetragonioides and a commercial spinach variety under similar growth conditions and directly compare the levels of oxalate in both young and old leaves of these plants to perform a direct comparison.”

Tetragonia tetragoniodes, which is high in antioxidants as well as other minerals, nutrients and vitamins, is a common coastal and estuarine species of the Pacific region. It is native to New Zealand, Australia, Japan, Chile and Argentina.

Professor Barkla said Warrigal greens - also known as Botany Bay greens, tetragon, native spinach or New Zealand spinach – was eaten by both Indigenous Australians and the early settlers.

“Its use was first mentioned by Captain Cook who ordered that it be eaten by his crew on board the Endeavour to fight scurvy.”

Professor Barkla said Warrigal greens was a hardy crop and could be used to remediate salty soils.

“What makes this plant particularly attractive for cultivation is that it is significantly salt tolerant, showing the typical response of halophytes to salinity, with growth enhancement at low salt concentrations and tolerance of high salt concentrations, unlike most crop plants where soil salinisation results in unacceptable decreases in quality and yield.

“The cultivation of this native species would provide more options for landowners where the salt levels are already moderate to high, allowing for the increased use of degraded or marginal lands for agricultural production or the conservation or rejuvenation of ecosystems through the ability of this plant to bioremediate saline soils through the hyper-accumulation of salt from the soil into the aerial parts of the plant.”

Carolyn Vlasveld is assisting Professor Barkla during the month of January as part of the annual SCU Science Summer School. The Summer School is designed to give early career scientists experience in different aspects of research including field work, laboratory based activities, analysing data and writing up results and conclusions.

“It’s exciting to be part of this project,” said Carolyn, who plans to do post-graduate study focused on plant science.

“There are many Tetragonia plants back home in Melbourne. If I am able to find out that the levels of oxalic acid are okay then I’ll definitely be eating them.”
Photo: Associate Professor Bronwyn Barkla from Southern Cross Plant Science (left) and 2015 SCU Science Summer School student Carolyn Vlasveld inspect the Warrigal greens (Tetragonia tetragoniodes) in the greenhouse.