Can Australian Tree Ferns make Dogs have Hives?

my two pitbull puppies have been having hives for two days and after steroid and benedryl shots at the vet they are still comming back (the hives) and it occured to me that my two pit pups were standing in the dark when I let them out in the back yard licking the australian tree fern right before this occured. Could this possibly be the problem because I can't figgure it out.

According to this is does not cause allergic reactions nor is it toxic, but I am sure it is still possible to have a reaction that just has never been reported.http://www.hear.org/pier/wra/pacific/cyathea_cooperi_htmlwra.htm

Possibly, they are very itchy plants if you come into contact with them. Or your dogs could be more sensitive to them.