I guess it's time to talk about my fan theory of the Ra-Seru and their respective trees. Let's play match the 10 ra-seru with their respective trees and fate.

Rim Elm: Meta's egg was here.
Mt. Rikuroa: Terra's egg was here.
West Voz Forest: Ozma's egg was here.
East Voz Forest: Jedo's egg was here.
Jeremi: My speculation is that Mule's egg was here. Jeremi's tree is the only tree that's on top a seeminly human made construction. My theory is that it used to be on ground level but just like Sol's tree it turned into a seedling and was transplanted to the Sky Gardens. During the process the Egg was discovered and got out to the human world. The connection with Buma can be the nearby fishing pond.
Mt. Letona: Dohati manipulated Saryu to get ahold of this Egg and it ended in Dohati's Castle Mist Generator. It's very likely that considering the strong presence of the henchement of the mist in this area that this egg ended in a mist generator.
Sol: When the tree turned into a seedling the Egg was discovered and ended up as a prize in the Muscle Dome.
Buma: 1 of this is Horn the other 2 were used for Mist Generators. Since I think because of proximity Letona's matches with Dohati's Mist Generator pretty well the other 2 would have been used for Zora's Floating Castle and Zeto's Dungeon respectively.

I should clarify that it's heavily implied that the Absolute Fortress Mist Generator does not use an egg but rather the piece of Rogue that Cort has. Cort even says that if he dies the mist generator dies with him just like the connection between the other mist generation with their respecive eggs/ra-serus.

Also don't take any of this as me stating an absolute over anything. There's a lot of assumpions here. Though I'm also taking in-game hints/cues as well