Ergotamine (as the tartrate salt) is used in some migraine medications, Cafergot is the main brand name I believe, contains caffeine and ergotamine.http://neo.pharm.hiroshima-u.ac.jp/drug-info/img/ergotamine.gif
Here is the structure of ergotamine itself.
There are a while mix of ergoline alkaloids present in some natural sources also, morning glory (Ipomoea) seeds, Rivea Corymbosa, and a comparitively large amount is present in hawaiian baby woodrose (Argyreia nervosa), all these plants contain a varied mixture of ergolines, including d-lysergic acic amide, here's a link, its more aimed at recreational users of ergine containg seeds, but it does have a breakdown of the various quantities/ratios of alkaloids found in the differing species, if thats any use.http://www.clearwhitelight.org/hatter/lsainfo.htm
(Oh. and AFAIK, Argyria Nervosa seeds contain no cyanogenic glycosides, but rather, its an inherent property of LSA to cause nausea in many people if ingested.
By three forms, you may be thinking of the various stereoisomers of LSA/LSD, its a molecule large enough, for the stereochemistry, to become a pain in the arse sometimes.
The reason ergotamine is used for treating migraines, is that its a potent vasocontrictor, and vasodilation is one cause of migraine headaches, the fungus Claviceps Purpurea (ergot, hence the name) caused a lot of problems in the middle ages, as it is parasitic on rye and other grain species, it grows best by far on rye though, when the parasitised grain was processed and eaten as bread, it caused a poisoning known as St.Anthony's fire, andthought to be a punishment from above, as it took two forms, one primarily displaying gangrene, caused by the vasoconstrictor effects of the ergoline alkaloids in the contaminated bread, the other, a hallucinogenic form of poisoning, which quite probably was the worse of the two, as not only would you be stuck in a bad trip, but in those days, it might well have got you burnt at the stake as a witch.
Bread roll, anyone?