This planet, it turns out, is the prehistoric Earth. And yes, we are their descendants, as demonstrated not so much by shared DNA, but by shared attitudes and agendas:
"[...] Since we decided a few weeks ago to adopt the leaf as legal tender, we have, of course, all become immensely rich."For other money trees, see Kendrick Lamar, Nalo Hopkinson, Clifford D. Simak, and Adam Roberts.
Ford stared in disbelief at the crowd who were murmuring appreciatively at this and greedily fingering the wads of leaves with which their track suits were stuffed.
"But we have also," continued the management consultant, "run into a small inflation problem on account of the high level of leaf availability [...] we are about to embark on a massive defoliation campaign, and ... er, burn down all the forests. I think you'll all agree that's a sensible move under the circumstances."
This is not the first (supposedly) impractical currency in the novel:
"[...] Its exchange rate of eight Ningis to one Pu is simple enough, but since a Ningi is a triangular rubber coin six thousand eight hundred miles long each side, no one has ever collected enough to own one Pu. Ningis are not negotiable currency, because the Galactibanks refuse to deal in fiddling small change. [...]"Actually, a credit theory of money might say there's nothing wrong with the Ningi/Pu system. Owning a Ningi wouldn't have to involve re-locating a physical object: a record in a ledger should be enough. Compare the famous stone money of Yap.