| True Lilies (Lilium & Hemerocallis) | Deadly | Bouquet/cut-flower | Unidentified nephrotoxin in every part (leaf, petal, pollen, and even vase water) causing acute kidney injury in cats specifically |
| Sago Palm | Deadly | Houseplant | Cycasin, causing severe gastrointestinal injury and acute liver failure; seeds/nuts are the most toxic part |
| Oleander | Deadly | Garden shrub | Cardiac glycosides (oleandrin) throughout the plant that disrupt heart rhythm; toxic even dried |
| Lily of the Valley | Deadly | Garden | Cardiac glycosides (cardenolides such as convallatoxin) that affect heart rhythm; NOT a true lily but still life-threatening |
| Azalea / Rhododendron | Deadly | Garden shrub | Grayanotoxins that interfere with nerve, muscle, and heart function; even a few leaves can be serious |
| Foxglove | Deadly | Garden | Cardiac glycosides (digitoxin/digoxin-type) that act directly on the heart |
| Autumn Crocus | Deadly | Garden | Colchicine, an alkaloid throughout the plant causing multi-organ failure and bone-marrow suppression |
| Yew | Deadly | Garden shrub/hedge | Taxine alkaloids that cause sudden, severe heart rhythm disturbances |
| Castor Bean Plant | Deadly | Garden | Ricin, a toxalbumin concentrated in the seeds/beans; a single well-chewed seed can be lethal |
| Cyclamen | Toxic | Houseplant | Terpenoid saponins, concentrated in the tubers/roots; large tuber ingestion can affect the heart |
| Kalanchoe | Toxic | Houseplant | Bufadienolides (cardiac glycosides) that can, in larger amounts, disturb heart rhythm |
| Dieffenbachia | Toxic | Houseplant | Insoluble calcium oxalate crystals that embed in the mouth and throat, causing intense burning |
| Philodendron | Toxic | Houseplant | Insoluble calcium oxalate crystals causing oral and throat irritation |
| Pothos | Toxic | Houseplant | Insoluble calcium oxalate crystals causing mouth and throat irritation |
| Monstera | Toxic | Houseplant | Insoluble calcium oxalate crystals causing oral and throat irritation |
| Peace Lily | Toxic | Houseplant | Insoluble calcium oxalate crystals; NOT a true lily, so it does not cause the kidney failure that Lilium/Hemerocallis do |
| Tulip | Toxic | Garden / cut-flower | Allergenic glycosides (tulipalin A/B), concentrated in the bulb |
| Daffodil | Toxic | Garden / cut-flower | Lycorine and other alkaloids plus oxalates, most concentrated in the bulb |
| Amaryllis | Toxic | Houseplant | Lycorine and related alkaloids, most concentrated in the bulb |
| Hyacinth | Toxic | Garden / cut-flower | Alkaloids and oxalates concentrated in the bulb |
| Chrysanthemum | Toxic | Garden / cut-flower | Pyrethrins and sesquiterpene lactones |
| English Ivy | Toxic | Houseplant / garden | Triterpenoid saponins (hederagenin); the foliage is more toxic than the berries |
| Aloe Vera | Caution | Houseplant | Saponins and anthraquinones in the latex just under the leaf skin (the inner clear gel is considered non-toxic) |
| Snake Plant | Caution | Houseplant | Saponins that irritate the digestive tract |
| Eucalyptus | Toxic | Houseplant / cut-and-dried bouquet | Aromatic essential oils (eucalyptol/cineole); cats are especially sensitive to essential oils |