I found all the lightroots in the Depths. They give you an item that seems to do nothing. But at least it's not a golden turd like with the korok seeds on BotW.

https://detroitriotcity.com/media/b439c2137a5ff67961b706cbe4b18273ca2f80bb906e24c2592c305eddfe6141.jpg

https://detroitriotcity.com/media/c787dc7e6472feae43ebebb730e84ccd38137b1ff7b87670983f9701fd4f3763.jpg