Mesembryanthemum crystallinum is a prostrate succulent plant native to Africa, Sinai and southern Europe, and naturalized in North America, South America and Australia. The plant is covered with large, glistening bladder cells or water vesicles, reflected in its common names of common ice plant, crystalline ice plant or ice plant.
The plant usually uses C3 carbon fixation, but when it becomes water- or salt-stressed, it is able to switch to Crassulacean acid metabolism. Like many salt-tolerant plants, M. crystallinum accumulates salt throughout its life, in a gradient from the roots to the shoots, with the highest concentration stored in epidermal bladder cells. The salt is released by leaching once the plant dies. This results in a detrimental osmotic environment preventing the growth of other, non-salt-tolerant species while allowing M. crystallinum seeds to germinate.
In M. crystallinum, the number of seeds produced depends on whether CAM has been activated (C3 metabolism is more efficient) and the size the plant has grown to in its juvenile growth phase. During seed production, older portions of the plant progressively die off and dry out. The developing seed capsules continue to sequester salt and produce viable seeds. Seeds at the top of the capsule generally germinate immediately on imbibation while seeds at the base may remain dormant for longer than four weeks.