Warming to the Ice Plants

by Phil Watson

Carpobrotus rossii

Native Pig Face Carpobrotus rossii

The challenges of global warming are yet to be fully appreciated in relation to their potential impacts on our indigenous vegetation communities and the habitat they support for our threatened flora and fauna. One predicted response will be a relentless search for tolerant species suitable for landscape and revegetation sites which will be able to adapt to the harsher environment. Fortunately members of the ice plant family have a series of rare attributes which will enable them to flourish in these predicted climatic extremes. This article seeks to explore these attributes as well as highlight some of the fascinating cultural, historic and bush tucker values ascribed to its members.

Known botanically as the AIZOACEAE, (Latin for 'evergreen' or 'ever living'), the name reflects an ability to maintain green fleshy foliage in the harshest and driest environments. There are over 2300 succulents, herbs and shrubs in the family from South Africa, Asia, and North & South America. There are only 60 indigenous Australian species four of which occur in Tasmania. Disturbingly already over 20 naturalised South African invaders thrive in Australia's harsher locations suggesting climate change may exacerbate their invasive potential.

The family has 2 groups based on the presence or absence of petal-like staminoides (large sterile stamens). The sub family MESEMBRYANTHEMOIDES has showy daisy–like flowers made of these brightly coloured staminoides typically seen in native pigface Carprobrotus rossii, whilst the other sub family RUSCHIOIDES has small insignificant flowers which are brightly coloured on the inside as seen in bower spinach Tetragonia implexicoma.

Like many Australian species the Tasmanian representatives act as key framework species in saline wetlands and dry coastal communities. Local examples include the Pitt water and Lauderdale salt marshes as well as the remaining 100 kilometres of undisturbed sandy beaches vegetated by indigenous flora.

From an historic perspective immense significance can be directly attributed to two of the family's indigenous species: bower spinach and New Zealand spinach. It could be considered that these species are responsible for establishing Australia instead of colonial African nations as the preferred Penal colony.

Adaptive responses to the global warming challenge

Climate change's predicted warming, reduction of overland flows and reduced soil moisture will impose severe habitat limitations on our indigenous plants and animals. However certain plants within families such as the ice plants, native grasses POACEAE and the cactuses CACTACEAE will be advantaged and potentially increase their natural ranges. An obvious example will be kangaroo grass Themeda triandra which benefits from a more efficient photosynthetic process (known as a C4 pathway) enabling it to flourish in dry periods when most other grasses withdraw into dormancy. Interestingly, recent observations suggest an increased richness of native grasses on disturbed dark-soil grassy woodland due to their exotic competitors such as Yorkshire fog Holcus lanatus and quaking grass Briza maxima withering and dying under drought stress.

Remarkably, ice plants have evolved a separate mechanism and are known as 'night-time breathers' or technically crassulacean acid metabolism (CAM) that will increase the plants' adaptive capacity to climate change. By storing carbon in the form of organic acids produced during night time respiration they do not need to absorb carbon dioxide by opening their stomatal pores. Hence CAM plants stop moisture loss through their pores during the heat of the day. This endows them with added xerophytic abilities that enhance their succulency mechanism to accumulate moisture and halophytic characteristics to survive in highly saline areas. [i.e. they are drought resistant and salt tolerant. ED]

A family with many appealing names

The family members have intriguing common names, most relating to their ability to survive low moisture or high salinity conditions. The name 'ice plant' refers to their leaves being surfaced with salt accumulating bladder-like cells that often sparkle like ice granules to reflect sunlight and reduce transpiration. This name is applied to the fleshy-leaved South African ice plants Mesembryanthemum sp. and Lampranthus sp. as well as the previously mentioned bower spinach.

The aptly-named 'livingstones' or 'pebbles' Lithops sp. and livingstone daisy Doroanthemum bellidiformis are designed to mimic the colours and textures of surrounding stones and pebbles. This ensures survival during arid periods by imparting drought resistance and camouflage from foraging herbivores. During the rainy season when the desert is alive with edible vegetation they transform from their chameleon-like behaviour into large perfumed boldly coloured daisy–like flowers which attract passing insects or butterflies.

The term 'noonflower' is another common name given to some members of the AIZOACEAE family including the coastal noonflower Carpobrotus glaucescens, the roundleaf pigface (or noonflower) Disphyma crassifolium and many South African species. It refers to their habit of opening around noon and closing later in the day. The resulting carpet of pinks and yellows attract insect pollinators which are at their busiest at this time.

The less attractive common name 'snot wort' Conicosa pugioniformis relates to this succulent's slimy roots which are valued as a South African bush tucker delicacy.

The tasty 'greens' were highly valued by early explorers

Ice plants form an important historic connection with Tasmania's convict ancestry. This arose as a consequence of Captain Cook's 1768 voyage to observe the transit of Venus. He satisfied his scurvy-stricken crew's desperate need for fresh greens by harvesting the pot herb New Zealand spinach from the New Zealand shoreline. Following the discovery of large swards of both New Zealand spinach and bower spinach along the Australia coast by Cook and other explorers, they soon came to rely on these greens to enhance their Spartan rations. If the early explorers and colonists had shown a little appreciation for the Aboriginal way of life they would have selected today's popular bush tucker treats included sea-celery Apium prostratum and grey saltbush Atriplex cinerea instead of limiting their choice to only those plants that resembled English vegetables.

So impressed was Sir Joseph Banks with these ice plants, he sent seeds to Kew Gardens from where they rapidly gained favour in high society as a summer spinach. In 1779 Bank's fondness for this plant's ability to provide reliable nutritious greens was portrayed in the House of Common' inquiry into the suitability of Australia compared to West Africa as a convict-based colony. He obviously left a strong impression and the rest is now history.

Was 'pigface' Tasmania’s first bush tucker?

Tasman's voyage of 1642 was not only historically significant because of the arrival of the first explorers in Tasmania, but also because of the collection of 'greens' (recorded as a Mesembryanthemum sp) by his crew from the banks of the Boomer Creek flowing into Marion Bay. The collection of what is considered to be native pigface was reported to be

'not unlike a certain plant growing at Cabode Bona Esperance' (Cape Town).

Many diaries of early explorers and settlers not only record the edibility of these 'greens' but also draw attention to the unique strawberry/fig like flavour of the native pigface's fruits. During the late 18th century a number of explorers referred to the harvesting of ice plants for pot herbage or edible fruits. These included Bligh's 1788 visit to Adventure Bay, Bruny Island and D' Entrecasteaux's 1793 visit to Recherche Bay.

During this visit he noted that:

'the fruit proved a delicacy with the New Hollanders (Aborigines) and resembled the Hottentot’s Fig of South Africa (Mesembryanthemum edule) except that the flowers were not yellow but reddish purple'.

Settlers at Collin’s first settlement at Risdon Cove collected ice plants for nutritious 'greens' whilst inland explorer Edward John Eyre partook of pigface fruits, noting the ripe fruit was rich, sweet and refreshing in hot weather.

Robust landscape plants with weed potential

Australia has approximately 25 exotic species recognised as environmental weeds, a number of which derived from naturalising around old settlements, especially near the coast.

The Tasmanian weeds include noonflower Lampranthus glaucus, heartleaf iceplant Aptenia cordifolia, common iceplant Mesembryanthemum crystallinum, yellow pigface Carprobrotus edulis and angled pigface C. aequilaterus. Of these, the latter two present major concern as they are either out-competing native species or are being inadvertently planted by unaware, enthusiastic bush regenerators. Their ability to release hundreds of seeds when triggered by rainy spells or establish from fresh or even significantly dehydrated cuttings ensures they will remain a persistent threat. Given the recent enthusiasm for planting indigenous pigface, it is important to identify pigface positively before planting. Remember, if it has a yellow flower err on the side of caution and check it is not a weedy species!

Valuable 'people's plants' supplying food and medicine

It was apparent that explorers and colonists developed a strong desire for the tasty and nutritious green foliage of Tetragonia species. This attraction continued to gain momentum over the next two centuries with these pot herbs being cultivated in European gardens. They have now become an heirloom vegetable worthy of any menu, especially being suited to stir fries, spinach dishes and quiches. Of course, they also prove just as attractive to wildlife; hence protection from browsing is required during their establishment. Once growing vigorously the wildlife grazing can be used to advantage as marsupial pruning shears to limit their rampant growth!

It is important to be aware that, like rhubarb and silver beet, it is best not to over indulge due to the low levels of oxalates and saponins existing in the succulent leaves and stems.

In relation to the luscious fruits of native pigface local Aboriginals eagerly awaited their summertime ripening. Aboriginal family bands would often establish camp next to broad expanses of fruiting pigface in order to supplement their fish and seafood diets with otherwise difficult to find offerings of summer ripening bush tucker. They not only enjoyed the fruits but also cooked leaves of this native pigface or at times the roundleaf noonflower to accompany their pit-roasted possum, roo or echidna.

Beyond their bush tucker attributes, the leaves and stems when squeezed ooze a gel-like sap which acted as a soothing lotion in much the same way as Aloe vera. As an aside these bulky, sappy leaves have proven problematical for all those plant collectors and students who have attempted to use plant presses to dry and press specimens. They are a botanist's nightmare!

When exploring the worldwide range of extraordinary plant uses attributed to ice plants, it would be remiss not to mention the captivating mind and mood altering qualities (attributed to the alkaloid 'mesembrine') of the South African species known locally as 'Kanna' Sceletium tortuosum.

This plant has been used by hunter-gathers and pastoralists from prehistoric times to elevate mood and decrease anxiety, stress and tension. Amazingly larger doses have no severe adverse affects, as it induces a euphoric state enabling pastoralists to decrease thirst and hunger or for its application as a local anaesthetic and analgesic for tooth extraction. Traditionally prepared by crushing the succulent plant before sun drying prior to chewing, smoking, inhaling as snuff or brewing as a tea, it is an important child sedative and has been effectively used by indigenous healers to withdraw alcoholics from their addiction. Even now the plant may be called onse droe drank - 'our dry liquor'. Although once widely traded in the South African Cape province and stocked in trading stores, inventories of wild plants have dwindled due to over harvesting and habitat destruction. This has resulted in its replacement by alcohol, tobacco and cannabis. It is pleasing to note that, using only cultivated rather than wild harvested materials, currently phyto-pharmaceuticals from Sceletium are being extracted for clinical trials in readiness for the international market.

Finally it is worth reflecting on another South African pigface look alike known as 'Khadi Root' Khadia acutipetala. Its fleshy rootstock provides an alternative yeast source to act as the key fermentation agent in brewing a distinctively flavoured, yet extremely prized beer known as Khadi.

Conclusion

The ice plant family primarily consists of hardy resilient plants. Their tolerance is a consequence of their efficient methods of seed dispersal, ease of propagation from cuttings or offsets, their succulence, pest and disease resistance, fire resistance, xerophytic and halophytic abilities all supported by their CAM metabolism. In light of the global warming impacts, it is predicted that their recent popularity as landscape, erosion control, and bush tucker and revegetation species will increase. These competitive advantages will also result in the prevalence of many more exotic members becoming invasive weeds.

Many exotic and native members add a rare three dimensional element to landscapes. This is a consequence of their thick, succulent leaves symbolising shapes of limbs and fingers. They can provide an inspiring contrast with the two-dimensional, flat leaves of the most other plants in the landscape.

References:
- The term night time breathers was referenced from the Royal Tasmanian Botanical Gardens information sheet 'The Century Plant'
- Low, T. Bush Tucker Australia's Wild Food Harvest Angus & Robertson, Sydney, 1992: 134-135
- Potts, B. et al. (ed.) Janet Somerville’s Botanical History of Tasmania, 2006
- Ben-Erik van Wyk and Nigel Gericke People's Plants A Guide to useful Plants of Southern Africa Briza Publications 2003
[The common names in this article have been changed to conform to those in The little book of common names for Tasmanian plants (2001) by Hans & Annie Wapstra, Mark Wapstra & Louise Gilfedder, DPIWE. Hobart.]

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