Poisonous plants

Continuing my toxicology studying...(this is going to be a long one)

Most poisonous plants do not taste good. If you don't force the animals to eat them, they probably won't. (For a given definition of "force"...leaving a cat in the room with a lily may qualify as forcing the poor feline to chew on the plant).
Other definitions of "force":
-overgrazing
-underfeeding
-lack of forage (i.e. drought) or accumulation of toxins (ex. corn accumulates nitrates)
-misidentification

If the hay contains toxic weeds, stop feeding it. This may fix all the problems.

Berries are bad.

Common names are, well, common. Totally different plants may share the name.

Now, by system:

Cardiovascular
Cyanide and cardiac glycosides are the major toxins here. Oleander, Japanese Yew, and foxglove are potent, as are seemingly innocuous fruit trees like apple, apricot, and choke-cherry (which sounds totally innocuous, doesn't it?).
Kalanchoe has cardiac glycoside-ish substances, and it's sold as houseplant where it doesn't grow wild. But then, everything toxic seems to be sold as a houseplant. Like lily of the valley. And monkshood. And water hemlock.

Choke cherry (prunus virginiana)
delphinium/larkspur
foxglove (digitalis)
Japanese yew (taxus) has red berries with poisonous seeds. On the other hand, they've made a nice chemo drug with it now.
Kalanchoe causes vomiting, diarrhea, in addition to the CV signs. No struggling before death, cyanotic membranes, and petechial hemorrhages in the GI tract.
Lily of the valley (convallaria majalis) works through cardiac glycosides.
Monkshood (aconitum) grows in meadows and mountains.
Oleander (Nerium oleander) is very common in California. Do NOT toast marshmallows on sticks from oleander bushes.
Summer pheasant's eye (Adonis aestivalis) is similar to oleander and foxglove, horses and sheep are the usual victims.
Water hemlock (Cicuta maculata) is even more poisonous than poison hemlock, although it becomes deceptively palatable (to herbivores, presumably) after being sprayed with herbicide.

Blood
Bracken fern takes weeks to start causing bone marrow depression in cattle. Horses are done for by thiaminase and get neurologic signs.
Onions have n-propyl disulfides, which oxidize hemoglobin and cause weakness, depression, pale or icteric mucous membranes. Also GI distrubances, rapid pulse and respiration, and, of course, Heinz-body hemolytic anemia.
Red maple contains gallic acid in the wilted leaves, which kills horses by hemolytic anemia.
Sweet clover (melilotus), a question I got wrong on the neuropath exam, are only poisonous when dried improperly and make dicoumarol. Sheep are more resistant than cattle.

GI
Solanaceae: everyone's favorite little known fact is that tomatoes are related to nightshade! (a guy once tried to impress me with his knowledge of this fact, which would probably have gone over better had he not so obviously been clueless about anything and everything else botanical)
Other fun clinical signs: CNS depression, cardiovascular collapse, hallucinations (a specialty of Jimsonweed, aka datura).
Mountain laurel is related to azalea and rhododendrons, and its toxins can get into meat and honey.
Mayapple (sometimes called mandrake, though it's not the same plant as that mandrake). Vomiting, lethargy are the big clinical signs, but it can be treated with copious fluid therapy. Mayapple doesn't make much of a house plant, but it's sold as a lovely native plant for people doing shade gardening.
Sneezeweed is a direct GI irritant, seen in sheep in the west (where it's probably always overgrazed and droughty).
Tobacco.
Brunfelsia, known as Yesterday Today and Tomorrow, can cause seizures and resemble strychnine. Takes a long time for recovery.

Liver and skin
It turns out plant-filled diets contain phylloerythrin, which is a photosensitive compound that does really nasty things when it deposits in the skin and get exposed to sunlight. Cracking and sloughing sorts of things. Plants like St. Johnswort and tansy ragwort cause liver disease, and then photosensitization (pyrrolizidine alkaloids). Plants like alsike clover just cause photosensitization (mainly horses). Then there's cycad palm, which is just incredibly toxic. On the other hand, in more northern states where it never flowers, you don't have to worry about its seeds, which are the most toxic part.

Nervous system
Hemp grows wild and is occasionally eaten in complete innocence by pigs that are bedded on it. More often it is the basis of entertaining stories about teasing out the truth from people who bring their dogs in after the dog ate someone's stash...Expect nervousness, irritation, CNS depression, and coma. In the dog.
Horsetail shows up in forage. It's related to bracken fern, has the same thiaminase enzyme. Cows that eat it become hyperexciteable, stagger, tremble, lose weight and drop milk production.
White snakeroot also likes wetland areas. Its toxin is tremetol, which causes choke, from partial throat paralysis, and trembling in horses.
Yellow star thistle causes what is sometimes called "chewing disease". Horses develop a very focal lesion at the nigropallidal...um...spot.

Musculoskeletal
Black walnut shavings are used for bedding, and then cause laminitis, severe edema, and ultimately severe GI signs in horses.
Hoary alyssum creates similar problems when it shows up being fed in hay.

Well, that was a brief section.

Renal
Oxalates!
Also alkaloids.
Autumn crocus, honestly, affects the GI more, but colchicine alkaloids in the bulb still do irreversible kidney damage.
Death camas show up most in the western states--they're occasionally mistaken for onions, it seems.
Philodendron, peace lily, dieffenbachia (dumbcane) are all oxalate containing houseplants. Dumbcane is especially interesting--its cells eject calcium oxalate when it is chewed, which makes the throat swell up (rendering the chewer dumb).
Easter lily is the culprit of the cat-in-a-locked-room mystery (at least back before anyone realized that lilies were quite that toxic to cats--or that cats would eat something that was so completely deadly).
Greasewood and halogeton (Jack-in-the-pulpit, another native shade plant) contain oxalates that really screw up rumens and cause other problems for grazing animals.

Reproduction
Goats that eat avocado plants get mastitis.
Locoweed interferes with estrus cycle.
Lupine--which is actually grown as forage for cattle-- causes crooked calf syndrome if the cow eats it between days 40-70 of gestation. The calf may be born with cleft palate or more severe signs.
False hellebore, also known as corn lily, causes "cyclops lambs".
Poison hemlock, which is related to carrots of all things, is most famous for being used to kill Socrates (or was it actually water hemlock?)
Ponderosa pine can cause abortions.
White snakeroot is secreted in milk--that's the one that killed Lincoln's mother.
Then there's castor bean, a lovely toxic looking ornamental that contains ricin, one of the most toxic substances known to man.