This is not true. Both of these plants contain calcium oxalate crystals that are basically little needles that can cause mild oral and gastrointestinal irritation in most cases. Pothos, the popular house ivy plant that many members have in their tanks, also contains these calcium oxalate crystals.
These crystals cause physical irritation upon ingestion of the roots, stems, or leaves, but unless your fish (or any animal for that matter) are consuming large amounts of these plants there shouldn't be any issues. As mentioned, tons of people have pothos in their tanks and there doesn't seem to be any issues. Although it is possible to have a problem if these are broken or scratched releasing some of these crystals, you would need to really smash them up before enough would be released to see skin irritation.
Here are some nice online resources for plant toxicology:
ASPCA's website
University of Pennsylvania School of Veterinary Medicine's Website
USDA's Website
*
Canadian Poisonous Plants Website
As far as texts go, I'm not too familiar with laymen texts, but
[FONT="]A Guide to Plant Poisoning of Animals in North America[/FONT] by Anthony Knight and Richard Walter is a nice reference.