Mesembryanthemum is a genus of flowering plants in the family Aizoaceae, order Caryophyllales, indigenous to southern Africa. The genus is named for the striking behaviour of its flowers: blooms open wide in full sunlight and close tightly at night or in overcast conditions, an adaptation that protects reproductive organs from dew, frost, wind and potential predators during periods when pollinators are unlikely to be active.
Many species in the genus are commonly known as ice plants, a name that refers to the glistening, globular bladder cells that cover their stems, fruits and leaves, causing them to sparkle like ice crystals. In South Africa the plants are collectively called vygies, from the Afrikaans word vy (fig), a term that extends more broadly to many plants in the Aizoaceae family. Raphides — needle-like calcium oxalate crystals — are found in abundance throughout the genus.
The genus belongs to the large and diverse family Aizoaceae, which is centred on the succulent-rich Greater Cape Floristic Region. Mesembryanthemum was historically a catch-all genus, and numerous species formerly placed within it have since been reclassified into segregate genera such as Cleretum and Carpobrotus, though circumscription varies between sources. Plants of the World Online recognised 108 species as of March 2019.
Several species are cultivated as ornamental plants for their showy, daisy-like flowers. Ornamental plants can escape into the wild, and the genus has become widely naturalised outside its native southern African range, where some species are considered invasive weeds.
Etymology
The genus name was coined by Jacob Breyne in 1684 as Mesembrianthemum, from the Greek μεσημβρία ("noon") and ἄνθεμον ("flower"), reflecting the midday flowering habit of species known at the time. In 1719, Johann Jacob Dillenius changed the spelling to Mesembryanthemum ("flower with the pistil in the center"), reinterpreting the first element from Greek μεσος ("middle") and ἔμβρυον ("pistil" or "embryo"), after discovering that some species flowered at night. Carl Linnaeus adopted the Dillenius spelling, and the International Code of Botanical Nomenclature requires retention of that original deliberate spelling.
Distribution
Mesembryanthemum is indigenous to southern Africa, centred on the succulent karoo and fynbos biomes of the Greater Cape Floristic Region. Several species have been introduced widely as ornamentals and have escaped cultivation, establishing naturalised populations across the Mediterranean basin, California, Australia and other regions with a similar climate; in some of these areas individual species are regarded as invasive weeds.
Cultivation
Species of Mesembryanthemum are frequently cultivated as ornamental plants for their brilliantly coloured, daisy-like flowers that open in full sun. They are well suited to dry, well-drained soils and sunny positions, reflecting their origin in seasonally arid southern African habitats. Their ease of cultivation has contributed to their naturalisation in Mediterranean-climate regions worldwide, and some populations have become weedy in disturbed ground.
Taxonomy Notes
Mesembryanthemum has historically been treated as a large, broadly defined genus, and many species once placed within it have been reassigned to segregate genera — most notably Carpobrotus (sour figs) and Cleretum — as systematic understanding of Aizoaceae has improved. Sources differ on exact circumscription, reflecting ongoing revision of the family. GBIF currently lists the genus under family Aizoaceae, order Caryophyllales.
