If you can't identify a plant, don't feed it to your pet! 

Nurseries, agricultural extension agents, botanical gardens and arboretums, and various books and websites are available to help you identify plants.  Plants often have different common names throughout the country so make sure you know the scientific name of the plant in question otherwise you might end up with the wrong information.

A good guideline is to only feed plants that you can find proof from multiple sources that they are safe to eat.  Just because something has an edible fruit or nut does not mean any other part of the plant is edible!  Also, just because a leaf may be edible it does not mean the fruit or seeds or roots are edible!

If you are landscaping an enclosure for your birds, tortoises, herbivorous lizards, or rabbits, you should make sure that all of the plants are definitely nontoxic.

The following list of plants are toxic and should never be fed to your pets:

Acokanthera – Acokanthera species (all parts toxic, except ripe fruit)
Amaryllis – Amaryllis species
Angel’s Trumpet – Datura species (leaves, seeds, flowers)
Apricot – Prunus armeniaca (pits, leave and bark)
Apple – Malus spp., (seeds, leaves, bark)
Avocado – Persea americana (pit, leaves, unripe fruit, stems)
Azalea – Rhododendron canadenis
Balsam Pear, Bitter Melon – Momordica charantia
Baneberry – Actaea rubra, A. pachypoda
Belladonna – Atropa belladonna
Bird of Paradise – Poinciana species (seed pods and flowers)
Bittersweet – Celastrus species
Black Locust – Robinia pseudoacacia
Boxwood – Boxus species
Braken Fern – Pteridium aquilinum
Buckthorn – Karwinskia humboldtiana and other species
Burdock – Arctium species
Buttercup – Ranunculus species
Caladium – Caladium species
Calla Lily – Zantedeschia aethiopica
Catclaw Acacia – Acacia greggii (twigs and leaves)
Caster Bean – Ricinus communis
Cherry – Prunus species (pits, leaves and bark)
Chinaberry – Melia azadarach
Clematis – Clematis montana and related species
Coral Plant – Jatropha mutifida
Crocus – Cholochicum autumnale
Cycad or Sago Cycas or Sago Palm – Cycas revoluta (Note: there are many other cycads and all should be considered poisonous)
Daffodil – Narcissus tazetta
Daphne – Daphne mezerum
Death Camas – Zigadenus venenosus and related species
Delphinium – Delphinium species
Dieffenbachia (dumb cane) – Dieffenbachia species
Eggplant – Solonum melongena (unripe fruit, leaves)
Elderberry – Sambucus mexicana
Elephant’s Ears or Taro – Colocasia spp.
Euonymus – Euonymus species
European Pennyroyal – Mentha pulegium
Four o’clock – Mirabilis jalapa
Heliotrope – Heliotropium spp. (leaves)
Henbane – Hyoscyamus niger
Holly – Ilex aquifolium and related spp. (leaves, berries)
Horse Chestnut – Aesculus hippocastanum and related spp.
Horse Nettle – Solanum carolinense
Hyacinth – Hyacinthus orientalis
Hydrangea – Hydrangea species
Iris – Iris species
Ivy (Boston, English and some others) – Hedera species
Jack-in-the-Pulpit – Arisaema species
Jerusalem Cherry – Solanum pseudocapsicum and related species
Jonquil – Narcissus jonquilla
Juniper – Juniperus species 
Lantana – Lantana camara and related species
Larkspur – Delphinium species
Laurel – Kalmia species
Lily-of-the-Valley – Convalleria majalis
Lobelia – Lobelia species
Locoweed – Astragalus species and Oxytopis species
Lupine – Lupinus species
Marijuana – Cannabis sativa
Milkweed – Asclepias species
Mistletoe – Phoradendron villosum
Mock Orange – Philadelphus species
Moonseed – Menispermum canadense
Monkshood – Aconitum species
Morning Glory – Ipomoea violacea (seeds)
Mushrooms – Amanita species and many others
Narcissus – Narcissus species
Oak – Quercus species
Oleander – Nerium oleander
Peach – Prunus persica (leaves, pit, bark)
Pear – Pyrus spp. (leaves, seeds, bark)
Peony – Paeonia officinalis
Periwinkle – Vinca minor, Vinca rosea
Peyote – Lophophora williamsii
Philodendron – Philodendron species
Plum – Prunus spp. (leaves, pit, bark)
Poison Hemlock – Conium maculatum
Poison Ivy – Toxicodendron radicans
Poison Oak – Toxicodendron diversilobum and T. querciflium
Poison Sumac – Rhux vernix
Poinsettia – Euphorbia pulcherrima and all related species
Poppy – Papaver somniferum and related species
Pokeweed – Phytolacca americana
Potato – Solanum tuberosum (sprouts, leaves, berries, green tubers)
Primrose – Primula species
Privet – Ligustrum vulgare
Ragwort – Senecio jacobea and related species
Red Maple – Acer rubrum
Rhododendron – Rhododendron species
Rhubarb – Rheum rhabarbarum (leaves)
Rosary Pea – Abrus precatorius
Sage – Salvia officinalis
Shamrock Plant – Medicago lupulina, Trifolium repens, Oxalis acetosella
Skunk Cabbage – Symplocarpus foetidus
Snowdrop – Galanthus nivalis
Sorrel – Rumex species, Oxalis species
Spurges – Euphorbia species 
Star of Bethlehem – Ornithogalum umbellatum
Sweet Pea – Lathyrus odoratus
Tobacco – Nicotiania spp.
Tomato – Lycopersicon esculentum (stems and leaves)
Tulip – Tulipa spp.
Virginia Creeper – Panthenocissus quinquefolia
Vetches – Vicia spp.
Water Hemlock – Cicuta spp.
Waxberry – Symphoricarpos albus
Wisteria – Wisteria spp.
Yew – Taxus spp.