The Lafrescia Seed is a key-item that is only found in Dark Cloud 2.
Its in-game description reads : "The seed of the Lafrescia plant. Where to plant it?"
This key-item is given to Max and Monica by Jurak. When asked about Griffon, Jurak does not seem to remember anything about him. When you've progressed enough in the Georama, come back to talk to Jurak : when asked about the Rainbow Butterfly, Jurak will say that it is rare but not evil !
Jurak will then state that the Rainbow Butterfly may be found near a Lafrescia plant : it gives to the 2 characters a Lafrescia Seed in order to develop the said plant.
This key-item, like most of them can't be spectrumized, it can't be sold, too.