Arctotheca calendula has different forms, some with dark centres like the ones in picture, others with light centres. Some forms are annual plants whilst some are perennial; the dark centred one is said to be the annual form. This is different to some other Asteraceae flowers where the disc flowers are still closed in the dark disc ones and open in the light coloured (yellow ones), as in Arctotis fastuosa.
It may in some conditions be a quite vigorous creeping plant that can invade large open patches. In Australia the Cape weed is quite a problem plant. It is more common in the winter rainfall area of South Africa in the south west of the country, but you will find it also in some of the eastern parts of the Karoo where conditions may be favourable.