Flame lily, Sinhala Niyangala, (නියඟලා) Extremely poisonous and beautiful.
Had a term like, Wifes Friend in Sinhala. Cook the yam with potatoes and give the husband to get rid of him. Luckily hard to find, so would have be really long premeditated murder.
It is also the national flower of Tamil Eelam, and as such was displayed during Maaveerar Day and the state flower of Indian state of Tamil Nadu (Tamil: senganthal (செங்காந்தள்) or kanvali kizhangu (கண்வலிக்கிழங்கு)).
This plant is poisonous, toxic enough to cause human and animal
fatalities if ingested. It has been used to commit murder, to achieve
suicide, and to kill animals. Every part of the plant is
poisonous, especially the tuberous rhizomes (yams).
Research paper cause was found because the patient finally said he had consumed with the intention of committing suicide.
It also takes 10-12 hours for effects to be seem. The longer a poison takes, the better for the poisoner. i.e. A wider range of potential poisoner suspects.
*Thanks Suchetha Wijeynayake for the tip on the paper.