This gorgeous plant is called Mesembryanthemum. It is currently in flower in Tunis. Everything about it is so pleasing to the eye. Its colour, the shape of its petals, the contrast between the flower and the fleshy leaves. Here is an informative extract from the Wikipedia website and it provides more detailed information then my amateur but nevertheless enthusiastic rambling remarks.
"Mesembryanthemum (meaning "midday flowering") is a genus of plants native to southern Africa.Mesembryanthemum is a member of the family Aizoaceae; many members of this family including the present genus are characterized by long lasting flower heads. Flowers of Mesembryanthemum protect their gametes from night-time dews or frosts but open in sunlight. There is obviously the evolutionary advantage of doing this; where sun, dew, frost, wind or predators are likely to damage exposed reproductive organs, closing may be advantageous during times when flowers are unlikely to attract pollinators.
Ornamental Mesembryanthemum may escape into the wild and consequently has become widely naturalized outside their native range. They are considered an invasive weed in certain places. Some species are hallucinogenic plants and as such may be subject to legal restrictions (e.g. Louisiana State Act 159)."