Yes, Parsley is toxic to dogs!
Dogs accidentally consuming the Parsley plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Parsley consumption is also toxic to Cats and Horses.
Toxic Principles Of Parsley: Furanocoumarins.
More Info About The Parsley Plant
Scientific Name: Petroselinum crispum
Family: Apiaceae.
Also known as: Italian Parsley, Hamburg Parsley, Turnip-rooted Parsley.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.