Wikipedia
Osladin
Osladine is a naturally occurring, high-intensity sweetener isolated from the rhizome of Polypodium vulgare. It is a saponin, sapogenin steroid glycoside, 500 times sweeter than sucrose.
A related compound, polypodoside A, has been identified from Polypodium glycyrrhiza and is 600 times sweeter than a sucrose solution at 6%.