The Swiss chard vegetable belongs to the Amaranthaceae family. Collard greens are part of the Brassica oleracea species, which includes many other plant species, such as cabbage, cauliflower, broccoli, and kale.
“Chard” comes from the Latin word carduus, which means artichoke thistle. The “collard” etymology is much easier. The term comes from a medieval word used to describe non-heading brassica crops.