We bought a couple of theses at the rainbow grocery in san fransisco. (we didn’t attempt to open them or eat them though). I gave one to my brother as a birthday present and the other is propped up in the cabin as a good luck charm…let me know what it tastes like…it could be the ‘last emergency’ rations on board.

A cross post to chowhound yeilded an answer. These are Trapa bicornis also known as Bat Nut, Devil’s Pod, and Ling Jiao. It’s an water plant related to the water chestnut.

Toxic when eaten raw. Ooops. Take those away from the pregnant lady. We’ll try boiling them to see if they taste better. We didn’t eat very much (less than one nut).

I did some research on Acacia as well and it’s a pretty interesting plant. The leaves and bark contain tryptamine alkaloids including DMT (some species more than others). Whether you would get any from eating the nuts is hard to tell from my brief reading. In any case the DMT would be metabolized unless you mixed in some sort of MAO inhibitor.

We were give similar ‘stuff’ by the village kids on isla Roatan (Honduras). The shape is quite different… but the hard shell and white insides are similar. I think what we had were pods from a jungle Acacia. You had to crack them open with a rock or hammer… and then picked the white, fluffy material from around the seeds.

The filling had a very odd texture… light, dry, but melted in your mouth… maybe like a merengue… as I recall, they tasted vaguely like vanilla custard.
(which is what the kids were after).