The derivation is lost in the mists of time. Some ideas here on Wikipedia.
Yellow flowers spotted yesterday.
Firstly the Ice Plant shown a few days ago.
An excellent ground cover plant very tolerant to drought:

Another excellent ground cover plant, drought tolerant:
A Sedum but I forget which:

Dandelion. Loved by insects and the bane of many a gardener:

Buttercup. Far too many in my lawn. As a child did you ever hold one under someone's chin to see whether the reflected yellow Sunlight showed they liked butter?

My tomato plants flowering nicely:

Lincolnshire wouldn't be the same without its glowing fields of Oilseed Rape:

All taken with the iPhone 6s in spite of what Flickr says