manchineel

The poison in this case is supposed to have been the Manchineel (Hippomane).

The poisonous manchineel was observed, a drop of whose milky juice will burn the flesh like vitriol.

I took one and cut it in two, remarking that it contained a circle of seeds or pips, instead of the stone of the manchineel.

"You went to sleep under the shade of some poison-trees, manchineel trees, we call them here," the doctor explained.

Especially I warned them against the manchineel, which ought to grow in this part of the world.