https://en.m.wikipedia.org/wiki/Glaucus

>the magical herb grew on the island Thrinacia sacred to Helios and served as a remedy against fatigue for the sun god's horses.

https://en.m.wikipedia.org/wiki/Cynoglossum_officinale
I think it's this.

I was looking up the white bull, father of the minotaur and got side tracked.