Are lilac leaves poisonous to dogs?

There are many plants toxic to cats. Below is just a few sites that list toxic plants.

http://www.aspca.org/pet-care/poison-control/plants/plant-list-cats.html

http://www.cfainc.org/articles/plants.html

http://www.sniksnak.com/plants-toxic.html

http://cats.about.com/od/catsafety/ss/toxicplants.htm

http://www.mycatsite.com/cat-health.html