Cassia fistula is tree with yellow flowers. As a medical student what amazes me is that the word fistula implies other meanings. A fistula, at least in medical science refers to a tract with two epithelial openings.
The botanic and medical term fistula is directly derived from the latin word fistula meaning tube or pipe.
Both the medical fistula and the fruits of the Cassia fistula tree show phenotypes similar to a tube.
I will spare everyone the medical example picture, but here are the fruit of Cassia fistula, which are sold as "manna":