The flowers and tree are growing in loam near Antonica's House of Pottery( 714, -17, -279 ) . They're house items that you'll have to move. If you lose a flower, Guard Delin can recreate some.
Pick them up one at at time (don't forget the tree!). Take them to the pretty area with flowers and vines around 690, -16, -255 . Like any house item, they turn green when you can place them. Put them on the ground (not on the rocks) near the vines.If they aren't near the vines you'll get a message prompting you to move it to the false grove.
When you've moved all the plants, hide in the fern at 672, -16, -241 and wait for the assassin. When he shows up, defeat him. This is a very tough fight, as he has reinforcements.