Warrigal Greens/Tetragon (Part 18)

Tetragonia tetragonoides [plant - Syd Olym Pk] sml.jpg

Warrigal greens, Sydney Bicentennial Park. © JPM, 2022.

The world's first native Australian weed, it's as good a substitute for spinach as you can find!

Names

Hailing from the exclusively southern-hemisphere genus Tetragonia (T.), a group of plants with at least 85 catalogued species, these fleshy trailing creepers go by quite a number of names both botanically and colloquially. Botanically, the most common species in Australia are as follows: T. tetragonoides, otherwise known as warrigal greens, New Zealand spinach, Botany Bay spinach, Cook's cabbage, sea spinach and tetragon, and in New Zealand as kōkihi in the Maori language; T. implexicoma, also known as bower spinach; T. eremaea; T. moorei; T. cristata, which could also be called crystal spinach; T. diptera; and T. decumbens. There are several dozen other species in Australia, but they are little researched and photographed and thus not worthy of further mention. In the article to follow, I refer to all species generally as tetragon, and the other species specifically by either their botanical or colloquial name.

These plants have been long known and utilised in Africa and are occasionally known as African spinach, the most common species of which, not found naturally in Australia, is T. nigrescens. African species will not be otherwise covered here.

Habitat and Range

Tetragon are, surprisingly, saline and clay-loving herbaceous plants. They can be found in the dune lines just behind beaches along most of the sub-tropical coast of Australia; clambering over rocky outcrops near the ocean; behind mangroves and estuary regions, usually just above the waterline; and in desert dunes, salt and clay pan regions such as Lake Eyre and the Red Centre. Wherever there is salinity, tetragon are sure to find a home nearby. Tetragon dislike the humidity of the tropics, not typically being found further north than Rockhampton in the east, Alice Springs in the centre and Exmouth in the west.

Tetragonia as a genus has global distribution, but originally limited to the southern hemisphere, especially southern Africa, Australia, New Zealand and some Pacific islands. It was encountered by Captain Cook in New Zealand and again in Botany Bay. Taken to England in the late 18th century by Joseph Banks, the Australian species T. tetragonoides became the first Australian plant to be cultivated internationally as a vegetable and soon became an invasive, non-native weed wherever it was introduced, including in the United States and Europe.

In its native habitat of Australia, T. tetragonides, more commonly called warrigal greens nowadays, can be found along the east coast from Bundaberg down to Melbourne; Tasmania and Flinders Island; northern and western NSW, especially north of Dubbo into southern-central Queensland; throughout South Australia, especially between Lake Torrens and Lake Frome and the Innamincka region; and lastly the Perth and Albany regions of Western Australia. Bower spinach, T. implexicoma, can be found on much of the southern Australian coastline from Geraldton in WA, all along WA southern coastline, the SA and Victorian coastlines and as far east as Eden in southern NSW, and the Tasmanian coastline. T. eremaea is common inland, especially in western NSW, eastern, central and southern SA, and central & southern WA. T. moorei is common west of Griffith along the Murray-Darling rivers heading into SA, especially the Mildura district, and also west of Bourke, NSW; in SA around Innamincka & Strzelecki deserts; and in WA in the mid-west & Esperance Gold fields regions. T. cristata can be found only in the Mid-west region of WA, in clay soils or granite outcrops, often alongside T. diptera which can also be found in Gascoyne and the northern wheat-belt regions of WA. T. decumbens occurs only on the WA coast from Geraldton to Busselton.

Figure 1. Distribution of Tetragonia (all species) across the continent. Atlas of Living Australia.
Tetragonia distribution map.png


Identification

Key Identifying Features
  • Fleshy, spinach-like leaves, either large, 5+ cm (T. tetragonoides) or small, 2-5 cm (all the rest).
  • Trailing, long stems, usually green or red in colour
  • Prominent papillae ("water drops") on the leaves, stems and seed pods
  • Four- (rarely, five-) petaled, yellow or pale yellow-green flowers at the leaf joints
  • Tough, four-cornered ('horned') green seed pods along the stems at the leaf joints
  • Red fruit (T. implexicoma only)
Tetragon leaves are probably its key identifying feature. They are typically a triangular, arrow-head shape. Some species, like warrigal greens (T. tetragonoides), can be large, from 3-15 cm in length. Other species like the bower spinach (T. implexicoma), T. eremaea and the West-Australian species are smaller, thinner and rounder in their leaf profile. Tetragon, especially warrigal greens (T. tetragonoides) and bower spinach (T. implexicoma), forms thick mats of foliage and stems where it grows.

Figure 2. Some very large, 10+ cm warrigal leaves (T. tetragonoides), the largest I have ever encountered. Bicentennial Park, Sydney. © JPM, 2022..
Tetragonia tetragonoides [leaves - Syd Olym Pk] sml.jpg


Figure 3. Smaller bower spinach leaves (T. implexicoma) are smaller, 2-4 cm, slightly rounder with more of an arrow-head shape. Great Ocean Road, Victoria. © JPM, 2022.
Tetragonia implexicoma [leaves - Great Ocean Road, VIC, 2022] sml.jpg


Figure 4. Foliage of T. eremaea, common in the saline inland regions of NSW, SA and WA. Atlas of Living Australia. © B. Corrigan, 2021.
Tetragonia eremaea [plant - ATLAS - B. Corrigan 2021].jpeg


Figure 5. Foliage of T. moorei, centre, with its fleshy, green leaves. Atlas of Living Australia. © J. Judy, 2020.
Tetragonia moorei [plant - ATLAS - J. Judy 2020].jpeg


Figure 6. Tiny leaves of T. diptera. There is very little information available about this plant, so perhaps it is best left alone. Atlas of Living Australia. G. Byrne, 2021.
Tetragonia diptera [plant - ATLAS - G. Byrne 2021].jpeg


Figure 7. The rounded foliage of west Australian T. decumbens. Atlas of Living Australia. © P. Crowcroft, 2022.
Tetragonia decumbens [plant - ATLAS - P. Crowcroft 2022].jpeg


All tetragon species exhibit papillae, which are a specialised type of swollen plant vesicle which contain water and salts. They look like permanent water droplets on the surface of the leaf, stem or seed pod. For some species, especially T. cristata and T. diptera (see figure 6 above and figure 10 below), the papillae may look like shards of salt or quartz. Papillae do not disappear readily when touched or rubbed gently. Papillae may increase or reduce in prominence depending on rainfall, with the generalisation that the more fresh water is available, the less prominent the papillae will be.

Figure 8. Papillae on the underside of a well-watered warrigal leaf (T. tetragonoides). Bicentennial Park, Sydney. © JPM, 2022.
Tetragonia tetragonoides [papillae - Syd Olym Pk] sml.jpg


Figure 9. Papillae on the underside of bower spinach (T. implexicoma). Great Ocean Road, Victoria. © JPM, 2022.
Tetragonia implexicoma [papillae - Great Ocean Road, VIC, 2022] sml.jpg


Figure 10. The crystal-like papillae of the Western Australian T. cristata. Atlas of Living Australia. © R. Davis, 2015.

Tetragonia cristata [plant - ATLAS - R. Davis 2015].jpeg


Stems are long and fleshy, typically green, but some species, like the bower spinach (T. implexicoma), can become brown and woody with age.

Figure 11. A thick mat of bower spinach (T. implexicoma) showing some new and old stems. Bower spinach often clambers over everything where it grows. Great Ocean Road, Victoria. © JPM, 2022.
Tetragonia implexicoma [plants - Great Ocean Road, VIC, 2022] sml.jpg


Flowers appear along the stem near leaf joints. They are usually yellow, white or cream with four petals (rarely, five) and 4-7 anthers surrounding a single, central pistil (see also figures 7 and 10 above).

Figure 12. Rarer five-petaled flowers, stem and seed pod of a warrigal plant (T. tetragonoides). Note the papillae along the stem as well as the leaves and pods. Bicentennial Park, Sydney. © JPM, 2022.
Tetragonia tetragonoides [flowers - Syd Olym Pk] sml.jpg


Figure 13. Close-up of a four-petaled flower on a warrigal plant (T. tetragonoides). Note the glistening papillae along the stem. Bicentennial Park, Sydney. © JPM, 2022.
Tetragonia tetragonoides [flower - Syd Olym Pk] sml.jpg


Figure 14. A white-flowered variant of warrigal (T. tetragonoides). Narabeen Lagoon. © JPM, 2022.
Tetragonia tetragonides [white flowers] 20221105_135946 sml.jpg


Figure 15. Four-petalled flowers on bower spinach (T. implexicoma). Great Ocean Road, Victoria. © JPM, 2022.
Tetragonia implexicoma [flowers - Great Ocean Road, VIC, 2022] sml.jpg


Flowers set into tough, green pods, with most species' pods exhibiting the distinctive four 'horns' and crystalline papillae (see also figures 4 and 5 above). The coastal bower spinach pods will turn red, toughening and turning woody as the pods develop the seeds inside.

Figure 16. Horned seed pods along the fleshy stem of a warrigal plant (T. tetragonoides). Make sure to remove these before cooking this plant. Bicentennial Park, Sydney. © JPM, 2022.
Tetragonia tetragonoides [seed pods - Syd Olym Pk] sml.jpg


Figure 17. Closeup showing the four horns of the seed pod. This feature is the meaning of the name 'Tetragonia' ('four-corners' in Greek). Narabeen Lagoon. © JPM, 2022.
Tetragonia tetragonides [pod] 20221105_135946 sml.jpg


Uses

All tetragons are edible as greens, although owing to their high levels of oxalic acid (just like spinach), they should be blanched and rinsed in cold water before consumption. They can be eaten fresh, sparingly, in salads, but excel as cooked greens in all manner of cuisines, from warrigal and ricotta pastries, to quiches, pies, soups, stews, stir fries, pickles and fermented greens. Any dish that would use spinach or silverbeet can be substituted with any Australian tetragon. We have cooked warrigal as a traditional Korean muchim, a steamed side-dish mixed with garlic and salted krill. Young, new leaves and stems are best, as older leaves can become bitter as they age.

Tetragon seed pods are extremely bitter and will leach a black, resinous substance when cooked that will stain whatever it touches. The pods and flowers are best removed and discarded prior to cooking or blanching the plant for consumption.

The soft flesh of the bower spinach (T. implexicoma) fruits are apparently edible, as long as they have not yet turned hard and woody.

Figure 18. Soft, red fruits of the bower spinach (T. implexicoma). I have not yet found these to try them. Atlas of Living Australia. © A. Melville, 2020.
Tetragonia implexicoma [bower spinach - fruit - ATLAS - A. Melville, 2020].jpeg


Warrigal greens have been extensively tested nutritionally. They have been shown to be extremely high in vitamin K; 100 grams (3.5 oz) of cooked leaves contains 278% of the recommended daily intake (RDI) of vitamin K, 25% of manganese, 19% of vitamin C, and 18% for vitamin D6. Other elements like calcium, iron, magnesium and vitamin B2 are also present in smaller quantities less than 10% RDI.

The Maori are known to have boiled kōkihi (warrigal greens) with the tubers of coastal convolvulus (a type of beach sweet potato, Ipomoea pes-caprae) in order to reduce their innate bitterness; I suggest simply removing the seed pods to decrease it. Regular sweet potato would make an ideal substitute for the less edible convolvulus nowadays if this traditional Maori recipe is ever to see the light of day again. The coastal tribes of Australia apparently never made use of the plant, although the desert tribes apparently learned of its nutritious qualities during the colonial era.

Tetragonia propagate readily from seed, but the seeds germinate best by being pre-soaked for 10 hours prior to planting (simulating the rain-germination method they use in the wild).

So, why do we grow spinach in Australia when we already have our own perennial version?
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