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Issue Number #38
Issue Date Winter 2007
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Title Warming to the Ice Plants
Author Phil Watson

This article will feature in two parts due to its length. Part one will introduce some of the fascinating attributes of the ice plants, whilst part two will discuss the interesting culinary and medicinal history of the plants. Part 2 will feature in the Spring edition of UnderStories. (ed.)

Introducing the Ice Plants

The challenges of Global Warming are yet to be fully appreciated in relation to their potential impacts on our vulnerable indigenous vegetation communities and the habitat they support for our threatened flora and fauna. One predicted response to the gradual global warming will be a relentless search for tolerant species, suitable for our future landscape and revegetation sites which will be able to adapt to the harsher environmental realities. Fortunately members of the Ice Plant family have a series of rare attributes which will enable them to flourish in these predicted climatic extremes.

Known botanically as the Aizoaceae, (Latin for "evergreen" or "ever living"), the name reflects the ability of members to maintain green coverage of fleshy foliage whilst existing in the harshest and driest environments. There are over 2300 succulent, herbs and shrubs in the family from South African, Asian, North and South American with only 60 indigenous Australian species (4 Tasmanian species). Disturbingly already over 20 naturalised South African invaders thrive in Australia's harsher locations suggesting Climate Change may exacerbate their invasive potential.

The family is composed of 2 groups, based on the presence or absence of petal-like staminoides (large sterile stamen). The sub family Mesembryanthemoides has showy daisy-like flowers made of these brightly coloured staminoides typically seen in Pig Face Carprobrotus rossii, whilst the other sub family Ruschioides has small insignificant flowers which are brightly coloured on the inside as seen in Tetragonia implexicoma.

Photo: Carprobrotus rossii. Photo by Richard Barnes

Like many of the 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 Tasmanian sandy beaches exclusively vegetated by indigenous flora.

From an historic perspective immense significance can be directly attributed to two of the family's indigenous species Tetragonia implexicoma and T. tetragoniodes (many common names apply such as Ice Plant, NZ Spinach, Botany Bay Spinach, Warrigal Greens and Cook's Cabbage). It could be considered that these species are held directly responsible for the choice of 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 competitively advantaged and potentially increase their natural ranges. Consequently they will attract attention due to their tolerance and adaptability. 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 the dry summer periods when most other competitive grasses withdraw into dormancy. Interestingly, recent observations suggest an increased richness of native grasses on disturbed dark-soil grassy woodland due to their exotic competitor grasses, such as Yorkshire Fog Grass, Holcus lanatus, and Quaking Grass, Briza maxima etc. withering and dying under drought stress.

Remarkably, Ice Plants have evolved a separate mechanism to be 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 loses 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.

A Family with many appealing Common Names

The family members are suitably bestowed with intriguing common names, most relating to their striking attributes which enable them to survive low moisture or high salinity conditions. The name of "Ice Plant" is linked with many family members mostly as a consequence of 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 previously mentioned T. implexicoma.

The aptly named "Livingstones" or "Pebbles" (Lithops sp.) and Livingstone Daisy (Doroanthemum bellidiformis) are robustly designed to mimic both the colour patterns and tough surface 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 in an attempt to gain the pollination services of passing insects or butterflies.

The term "Noon flower" is another popular descriptive name applied to family members such as the Australian Coastal Noon flower C. glaucescens, the Tasmanian salt marsh, Round Leaf Noon flower Disphyma crassifolium, as well as the many South African species such as Wiry Noonflower (Psilocaulon tenue), due to their habit of opening attractive blooms around noon and closing later in the afternoon. The resulting pinks, yellows etc carpets are irresistible to their insect pollinators which are at their busiest from noon to the mid afternoon.

The less than attractive common name "Snot wort" (Conicosa pugioniformis) relates to this succulent's slimy roots which surprisingly are valued as a South African bush tucker delicacy.

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 weed representatives including Noon Flower Lampranthus glaucus, Heart Leafed Ice Plant Aptenia cordifolia , Common Ice Plant Mesembryanthemum crystallinum and the South African Hottentot Fig or Sour Fig Carprobrotus edulis and the Chilean Pig Face C. aequilaterus. Of these, the later two present major concerns as they are either out-competing the native species or are being inadvertently planted by unaware, enthusiastic bush regenerators. Their ability to release 100's of seeds when triggered by rainy spells from the fleshy fruit or establishes from fresh or even significantly dehydrated cuttings ensures they will remain a persistent threat. Given the recent enthusiasm for planting indigenous Pig Faces, it is important to positively identify the Pig face before planting. Remember, if it has a yellow flower err on the side of caution and check it is not a weedy Sour Fig!

Conclusion

As alluded to earlier, the Ice Plant family primarily consists of hardy and environmentally resilient plants. Their tolerance is a consequence of their efficient methods of seed dispersal, ease of propagation from cuttings or off sets, 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, bush tucker and revegetation species will increase. Disappointingly these competitive advantages will also result in the prevalence of many more exotic members menacing indigenous vegetation communities as invasive weeds.


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