I'm pretty new to cake decorating, but I know enough to know that calla lilies are poisonous and should not be put on cakes, so when I showed up to my sister-in-law's wedding reception and the top tier was covered by them, I was appalled. I mentioned to a few people that it was poisonous, but no one thought anything of it. The lilies were just on the top tier, which is by now in my sister-in-law's freezer to save for her anniversary. Should I tell her it's poisonous? Is it a big deal? Would it be enough just to scrape off the top coat of frosting or should she not eat any of it? Also, should I mention to the cake decorator that this is not okay?

I did a little googling on it and it seems that while they are indeed poisonous, it is the stem liquid not the flowers themselves that are an issue in terms of touching the cake. If the stems have been wrapped or contained in some manner to prevent oozing onto the cake there won't be a problem. If your SIL's cake flowers were properly handled there is little risk for "poisoning" (which according to what I read is more like an allergic reaction rather than a life threatening problem as it is for dogs and cats who might bite into or eat the actual plant). Hard call on what you should do because I'm sure the flowers aren't still attached to the now frozen cake for her to inspect for safety.

Some info....

The calla lilies have but one flaw, which is that all parts of the plants are highly toxic if consumed by people or pets. All members of the calla family contain a poison known as oxalic acid. If ingestion is suspected, a poison control center should be contacted immediately. Early symptoms of poisoning include irritation and swelling of the mouth and throat, as well as acute and severe vomiting and diarrhea. Deaths have been reported in humans and in livestock. (From eHow)

Zantedeschia (Lily of the Nile or Calla lily) Zantedeschia is highly toxic and may be fatal if eaten. (From Wikipedia)

The above is about eating the actual flower not things which come into contact with the flower.

Tell your sister the above and let her make the decision of whether to go to her baker or not. If common sense prevails she won't eat the parts of the cake which came into contact with the lilies, it's her decision as to whether it is a big deal or not.

Thanks for the info! Now I wish I'd inspected the cake more.