I have purchased many packs and once got a Moon Flower from the Ravens Hoard pack, and have gotten two Bamboo Shoots from the Emperors Attic pack.
Both plants take an extraordinary long time to mature and then to become harvestable (42 HOURS for the Bamboo Shoots). Since I haven't harvested the Bamboo Shoots yet, I don't know what they drop.
My concern is that with these rare plants that are not auctionable, not dropped, and rare finds even in the packs, they should be giving another of their seed at Elder but the Moon Plant did not and I fear the Bamboo Shoots wont either.
I have already had to request help for the Bamboo Shoots, the card says they like Grapes of Wrath plants but they show no such like when planted next to one. I bought the Emporers Attic pack specifically to get the seeds so I would really like it if they worked.