If you've ever bought plants on
www.aquabid.com, you might have received a
FREE stem of a mystery plant from the seller. It's one way a seller can get good customer feedback and his/her way of saying thanks to the buyer for paying fast (or a lot of $$$

).
You must have seen those aquabid ads: "Anubias sp petite on driftwood with FREE Hemianthus callitrichoides"
Some of the online plant stores also include with an order a piece, sometimes tiny, sometimes a few stems, of a mystery plant to show their goodwill to buyers. And, of course,
on buying plants from APC members one most often gets a tiny (or not so tiny) bit of something unexpected. (I'm only talking about the good things - not the naughty hitchhikers).
I confess on several occasions it is the plant I ordered and paid for which I killed and it was the FREE mystery item which became a feature in the aquarium. Unexpected!
Long ago, I received one single stem of Rotala rotundifolia and now that is a thicket (the Didiplis diandra that was the main order has long gone!). Some Taiwan moss I received free, a tiny bit, is now a forest. The Elatine triandra ,which came free along with the (first) batch of Hemianthus callitrichoides (which I more or less killed), took off.
I think you get the picture. It must be some perversion of the Green Thumb Effect.
What is the best FREE plant/s you ever received?
Andrew Cribb