Yes, Lobelia is toxic to dogs!
Dogs accidentally consuming the Lobelia 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).
Lobelia consumption is also toxic to Cats and Horses.
Toxic Principles Of Lobelia: Lobeline.
More Info About The Lobelia Plant
Scientific Name: Lobelia cardinalis
Family: Campanulaceae.
Also known as: Cardinal Flower, Indian Pink.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.