Mesembryanthemum crystallinum
(crystalline iceplant)

M. crystallinum, commonly known as crystalline iceplant, is a prostrate halophyte native to north Africa, south-western Africa, western Asia and southern Europe. It has been both intentionally (as an ornamental) and accidentally (in sand used in ships ballasts) introduced into a number of countries in north and south America and Australia. This species is extremely stress-tolerant and during drought can switch from C₃ photosynthesis to Crassulacean Acid Metabolism (CAM). Throughout its life M. crystallinum accumulates salt which is leached from plants upon death. The increase in the concentration of salt prevents the establishment of native plant species enabling seeds of M. crystallinum to germinate and grow and dominate in the salt marsh habitat. Monotypic stands of this species have been reported in Australia and California, USA. In California it is also reported as being a major threat to Chorizanthe pungens var. pungens [C. pungens], a native species included on the California Native Plant Society (CNPS) Inventory of Rare and Endangered plants.

M. crystallinum is native to north Africa, south-western Africa, Western Asia and southern Europe. However there are differing views as to whether it is a native or non-native of southern Europe (Kloot, 1983; Weber, 2004). It has been introduced and naturalized in a number of countries including three states of the USA, Mexico, Australia and southern South America (Queensland Government, 2011).

It has been reported however that the distribution of M. crystallinum in Egypt is decreasing and under threat due to human activities (Abd El-Gawad and Shehata, 2014).

M. crystallinum produces a large number of seed which can be translocated into new areas by winds and by rabbits, rats and mice (AZ-WIPWG, 2005; Cal-IPC, 2015). It has a wide environmental tolerance and can grow in temperate climates and cold and warm deserts but is shade intolerant (AZ-WIPG, 2005).

M. crystallinum favours disturbed sites such as roadsides, cliffs, over-grazed areas and areas of coastal erosion, 0-100 m in altitude (FloraBase, 2015; Flora of North America Editorial Committee, 2015). It is however also found on undisturbed sites. It can grow well in saline environments and nutrient poor soils. 

Genetics

M. crystallinum has been reported to have a diploid number of 2n = 18 (Flora of North America Editorial Committee, 2015).

Reproductive Biology

There are five phases of growth for M. crystallinum; germinating seedlings, juvenile, adult, flowering fruiting and seed formation which respond differently to environmental stresses (Adams et al., 1998; Abd El-Gawad and Shehata, 2014). It flowers from early spring to summer, a process triggered by environmental stresses such as high salinity, drought or low temperatures. Flowers are hermaphrodite and are pollinated by insects. Flowers open during the day and close at and night (CSIRO, 2004). Under laboratory conditions M. crystallinum can produce around 15,000 seeds per plant (AZ-WIPWG, 2005). These may remain viable in the soil seed bank for up to two years (Plant Right, 2015). Seeds germinate during cold months and dormancy can be broken by any form of disturbance e.g. grazing, roads, drought and fire (Vivrette, 1999).

Physiology and Phenology

M. crystallinum is extremely stress-tolerant. During the dry season and periods of water stress, the mode of photosynthesis in adult plants of M. crystallinum switches from C₃ to Crassulacean Acid Metabolism (CAM). This enables the plant to open its stomata, mainly at night, allowing carbon dioxide to be fixed as malic acid which the plant then converts to carbohydrates by standard photosynthesis during the day (Schmalzer and Hinkle, 1987). This process enhances the net gain of carbon and therefore increases seed production (CSIRO, 2004). Once seeds germinate, seedlings undergo a period of rapid vegetative growth which stops during the summer season. Plants possess specialized trichomes called epidermal bladder cells which have a number of proposed functions. These include as a storage of water, accumulation of salts, protection from UV rays and a role in plant defense (Barkla et al., 2012).

Longevity

Depending on environmental conditions, M. crystallinum can be an annual, biennial or perennial (CSIRO, 2004). However, its lifecycle is usually completed within a number of months.

Population Size and Structure

In some parts of Australia where it has been introduced, M. crystallinum occurs as scattered patches (CSIRO, 2004). It can however form more dense mats which cover the ground when present in favourable environments. For example, monotypic stands have been recorded in parts of Australia and California (AZ-WIPG, 2005) and in Egypt, its native range (Abd El-Gawad and Shehata, 2014).

Environmental Requirements

M. crystallinum is found on a wide range of soils including those with high salinity, with varying moisture contents and pH though it’s found not to grow in areas of shade (Plants for a Future, 2015). It has been suggested that optimal growth of M. crystallinum is obtained with a moderate salinity, between 0.1-0.2 M of NaCl. Higher concentrations of up to 0.5 M are also tolerated but this level often triggers reproductive development (CSIRO, 2004). M. crystallinum is not tolerant of frost and plants are killed.

Environmental

• Land reclamation
• Ornamental
• Soil improvement

Human food and beverage

• Vegetable

Medicinal, pharmaceutical

• Traditional/folklore

M. crystallinum is morphologically similar to a number of species within the genus. These include M. nodiflorum and M. aitonis. However M. nodiuforum plants tends to be smaller, more upright with linear leaves overall and M. aitonis has fewer pimples and during flowering petals the same length as the sepals (CSIRO, 2015; Herbiguide, 2015).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

Physical/Mechanical Control

Small isolated plants can be removed by hand during the spring and early summer (FloraBase, 2015). Dense patches of M. crystallinum may be cut close to the ground (Weber, 2004).

Chemical Control

Some herbicide can be used to control dense patches but application is recommened before seed set (Weber, 2004). In Australia however, herbicide resistance has been reported (FloraBase, 2015).

23/09/15 Original text by:

Emma Thompson, CABI, UK