There is not much difference between them. Atropine and
Hysocyamine are isomers of each other. Atropine is (+/-)
Hyoscyamine, the tropic acid ester of tropine. The naturally
occurring alkaloid is (-) Hyocyamine. Thus it can be said that
Hyoscyamine is a racemic form of Atropine.
In other words, Atropine is a racemic variety of tropine
tropate, hysocyamine being the levorotatory enantiomorph of tropine
tropate.