The genesis of Plantagenet

I'm slowly working my way through the Book of Firsts, which I mentioned in an April post. It's divided into chapters for each of the A.D. (or C.E., whichever you prefer) centuries. I'm up to the 12th century, which includes the essay on "Who was the first Plantagenet king of England?" (Henry II.) It had two interesting word origins in it; the first was for Plantagenet, which came to be the name of the dynasty that ruled England from 1154-1485:

The man who became Henry II was a son of Matilda (daughter of Henry I) and thus a great-grandson of William the Conqueror. His father was Geoffrey, the great count of Anjou, who acquired his nickname of Plantagenet ("Sprig of Broom") from his sporting a sprig of yellow broom plant tucked into his helmet.

The OED says that the Plantagenet name wasn't common at the start, "only much later becoming associated with his descendants as a family surname."

Plantagenet comes from the post-classical Latin planta genista. I had to comb through a few OED entries to get this, but planta means "a young plant, seedling, slip or cutting," and genista is the Latin word for the broom plant and is now a genus name: "A plant of the genus (family Leguminosæ) represented by Dyer's Broom or Greenweed (G. tinctoria); the Common Broom (Cytisus scoparia) is by some referred to this genus."

I'll post about the second word tomorrow.