Twice, now, I have received a variety of catnip as part of an Adventure Awaits style collectable trade (this time, Madnip in an exchange with Sidney Price in the high school cafeteria for a postcard from Twinbrook), yet catnip varieties are part of no collection. They logically should be part of the Gardening collection, but are not.
Addendum: My sim later traded away the Madnip, and received nothing in return, earning her a well deserved What a Swindle! moodlet. This shows that catnip varieties appear as tradable collectables in the AA style collectable trades.
Addendum 2: When I later checked household inventory, I found a debug item whose image was just a red X on a white box which I couldn't put in world, salable for 1 simoleon. That's something that should not be received in a trade, if that was how I received it;
