I would be surprised if ricin and nigella are even in the
same family.
Ricin is Castor Bean, a tropical plant, that will grow to
15 feet high with wooly leaves, that are as big as dinner
plates. I have planted it, as it is said to run gophers off and may work....LOL
The seeds will kill a person and are beautiful, some about
a half inch oblong in red/brown/black mottled colors, shiny and pretty enough to use in necklaces....but deadly.
During the 60's someone imported necklaces for the hippies that had these seeds in them and killed a couple of kids.
Going from memory of a photo of Nigella, it is a small
flower and fine cut leaf, that is a vine and also there
may be a plant, but not in the castor bean family.
I have no idea what I copied then in post 2750.
It didn't translate in the Google Translate option.