|Carpobrotus edulis, West Coast National Park, South Africa|
Mesembryanthemum edule L
Carpobrotus edulis is a ground-creeping plant with succulent leaves in the genus Carpobrotus, native to South Africa. It is also known as Hottentot-fig, ice plant, highway ice plant or pigface and in South Africa as the sour fig (suurvy).
It was previously classified in Mesembryanthemum and is sometimes referred to by this name: Mesembryanthemum edule.
C. edulis is easily confused with its close relatives, including the more diminutive and less aggressive Carpobrotus chilensis (sea fig), with which it hybridizes readily. C. edulis can, however, be distinguished from most of its relatives by the size and colour of its flowers. The large, 2.5 to 6 inches (64 to 152 mm) diameter flowers of C. edulis are yellow or light pink, whereas the smaller, 1.5 to 2.5 inches (38 to 64 mm) diameter C. chilensis flowers are deep magenta. On the flowers, two of the calyx lobes are longer, extending further than the petals.
The leaves of C. edulis are only very slightly curved and have serrated sides near the tips.
In South Africa
The sour fig grows on coastal and inland slopes from Namaqualand in the Northern Cape through the Western Cape to the Eastern Cape. It is often seen as a pioneer in disturbed sites.
Flowers are pollinated by solitary bees, honey bees, carpenter bees, and many beetle species. Leaves are eaten by tortoises. Flowers are eaten by antelopes and baboons. Fruits are eaten by baboons, rodents, porcupines, antelopes, who also disperse the seeds. The clumps provide shelter for snails, lizards, and skinks. Puff adders and other snakes, such as the Cape cobra, are often found in Carpobrotus clumps, where they ambush the small rodents attracted by the fruits.
Ice plants grow year round, with individual shoot segments growing more than 3 ft (1 m) per year. Ice plants can grow to at least 165 ft (50 m) in diameter.
Flowers are produced mainly during late winter-spring (August–October). They open in the morning in bright sunlight, and close at night.
Carpobrotus edulis has naturalised in many other regions throughout the world, and is an invasive species in several parts, notably Australia, California and the Mediterranean, all of which have similar climates. The ice plant has escaped from cultivation and has become invasive, posing a serious ecological problem by forming vast monospecific zones, lowering biodiversity, and competing directly with several threatened or endangered plant species for nutrients, water, light, and space.
On the Mediterranean coast, Carpobrotus has spread out rapidly and now parts of the coastline are completely covered by this invasive species. Moreover, another invasive species, the black rat, has been shown to enhance the spreading of the ice plant through its feces. As the ice plant represents a food resource for the rat, both benefit from each other (invasive mutualism).
Although the ice plant may have arrived by ship as early as the 16th century, C. edulis was actively introduced in the early 1900s to stabilize dunes and soil along railroad tracks; it was later put to use by Caltrans for ground cover along freeway embankments. Thousands of acres were planted in California until the 1970s. It easily spreads by seed (hundreds per fruit) and from segmentation (any shoot segment can produce roots). Its succulent foliage, bright magenta or yellow flowers, and resistance to some harsh coastal climatic conditions (salt) have also made it a favored garden plant. The ice plant was, for several decades, widely promoted as an ornamental plant, and it is still available at some nurseries. Ice plant foliage can turn a vibrant red to yellow in color. Despite its use as a soil stabilizer, it actually exacerbates and speeds up coastal erosion. It holds great masses of water in its leaves, and its roots are very shallow. In the rainy season, the added weight on unstable sandstone slopes and dunes increases the chances of slope collapse and landslides.
The ice plant is still abundant along highways, beaches, on military bases, and in other public and private landscapes. It spreads beyond landscape plantings and has invaded foredune, dune scrub, coastal bluff scrub, coastal prairie, and, most recently, maritime chaparral communities. In California, the ice plant is found in coastal habitats from north of Eureka, south at least as far as Rosarito in Baja California. It is intolerant of frost, and is not found far inland or at elevations greater than about 500 ft (150 m).
Flowering occurs almost year-round, beginning in February in southern California and continuing through fall in northern California, with flowers present for at least a few months in any given population.
Removal of plants
Control of ice plants can be attempted by pulling out individual plants by hand, or with the use of earth-moving machinery such as a skid-steer or tractor, though it is necessary to remove buried stems, and mulch the soil to prevent re-establishment. For chemical control, glyphosate herbicides are used. Because of the high water content of shoot tissues, burning of live or dead plants is not a useful method of control or disposal.
It needs well-drained soil, a sunny position, and room to spread. It is an excellent evergreen, drought- and wind-resistant groundcover; it can be planted on flat, sandy ground, on loose sand dunes, lime-rich and brackish soils, and gravelly gardens, as well as in containers, rockeries, and embankments, and will cascade over terrace walls.
Its leaves are edible, as are its fruit, as with some other members of the Aizoaceae family. In South Africa the sour fig's ripe fruit are gathered and either eaten fresh or made into a very tart jam.
Rutin, neohesperidin, hyperoside, catechin and ferulic acid can be found in C. edulis, and contribute to the antibacterial properties of the plant. It also contains procyanidins and propelargonidins.
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