i now understand the difference, i saw plenty of both, i just got confused by 'spider lily' being applied to both. there are many images marked as spider lily that show both crinum asiaticum and hymenocallis. and of course i don't know all varieties of crinum. there are some with very skinny petals just like hymenocallis. the little 'corona' in the center is very characteristic though and is only on hymenocallis - so now i'll remember.
