List of toxic plants from Cornell University who listed them by their botanical names. I just went through their list and added the common plant name to the right.

By visiting their web site at: http://www.ansci.cornell.edu/plants/horselist.html
you can click on the botanical name to find more detailed information on just what classifies these as toxic.

A. muscaria = Fly Agaric, mushroom
A. pantherina = Panther, mushroom
A. verna = Destroying Angels, mushroom
Abrus precatorius = Rosary Pea
Acer rubrum = Red, Swamp, & Soft Maple
Acer saccharinum = Silver, Soft, & White Maple
Acer saccharum = Sugar, Rock, & Hard Maple
Allium spp. = Commercial, Wild, & Swamp Onions & Chives
Amanita spp. = Death Cap, Mushroom
Amsinckia intermedia = Fiddleneck
Apocynum spp. = Dogbane
Astragalus and Oxytropis spp. = Locoweed
Centaurea solstitialis = Yellow Star Thistle
Chenopodium album = Lamb’s Quarters
Cicuta spp. = Water Hemlock or Cowbane
Claviceps spp. = Ergot
Conium maculatum = Poison Hemlock
Coronilla varia = Crown Vetch
Datura spp. = Devil’s & Angel’s Trumpet
Digitalis purpurea = Foxglove
Equisetum arvense and other spp. = Horsetail
Eupatorium rugosum = White Snakeroot
Euphorbia spp. = Poinsettia, Spurges, Snow on the Mountian
Fagoypyrum esculentum = Buckwheat
Festuca arundinacea = Tall Fescue
Gelsemium sempervirens = Jessamine
Glechoma spp. = Ground Ivy, Creeping Charlie
Hypericum perforatum = St. Johns Wort, Klamath Weed
Laburnum anagyroides = Golden chain or Laburnum
Lathyrus spp. = Sweet Pea, Tangier Pea, Everlasting Pea, Caley Pea and Singletary Pea
Metilotus alba and Melilotus officinalis = White and Yellow Sweetclover
Nerium oleander = Oreander
Onoclea sensibilis = Sensitive Fern
Phytolacca americana = Pokeweed
Prunus spp. = Wild cherries, Black Cherry, Bitter Cherry, Choke cherry, Pine Cherry
Pteridium aquilinium = Bracken Fern
Quercus spp. = Oak Trees
Ranunculus spp. = Buttercups or Crowfoot
Rheum rhaponticum = Rhubarb
Ricinus communis = Castor Bean
Robinia pseudoacacia = Black Locust
Senecio spp. = Senecio, Groundsels, and Ragworts
Solanum spp. = Common and Black Nightshade, Horse Nettle, Buffalo Bur, Potato
Sorghum spp. = Sorghum or Milo, Sudan Grass and Johnson Grass
Taxus cuspidata = Yew
Trifolium spp. = Alsike, Red, and White Clover
Vicia spp. = Common, Hairy, Narrow leaved, and Purple Vetch and Broad Beans
Zigadenus spp. = Death Camas