That kind of spelling issue usually comes from "convention" or "established habit", rather than any consistant rule of idiom.
Is there a (canonical) source that has "Laveian" versus "Lavian"?
“Lave is most famous for its vast rain forests and the Laveian tree grub.” The adjectival form, when used in planet descriptions, is always generated by appending “ian” to the unmodified name.
Then I WILL correct the image after I log off... thanks.
(On second thought, as long as I have to correct spelling, I may as well make an animated gif.. only a few frames... color reduced... shouldn't be too much of a bandwidth hog)