The small marsh flower Cotula coronopifolia (also spelled C. coronipifolia) bears the common names brass buttons, golden buttons, and buttonweed. The flowers are bright yellow discoid inflorescences that look like thick buttons. Individual plants spread stems along the ground and send up the knobby flowers at intervals. The plant is native to southern Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, but it has been introduced to many regions of the world.
Brass buttons are common plants that occupy a specialized ecological niche

Ecological niche

In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...

.