My deep interest in the culture of the Chumash Native American tribes of southern California brings me to you, fellow nexians, to ask if you have, by any stroke of luck, any information about these relatively obscure species of tobacco:

Nicotiana attenuata ("Coyote Tobacco" )
Nicotiana quadrivalvis ("Indian Tobacco" )

and, in particular,

Nicotiana clevelandii

I haven't been able to find any stated active chemicals for these plants, so if someone else can find something, I'd be all ears. Also, on the off chance that anyone here has tried these, please, speak up.

There's some information on the traditional Chumash use of these in a book I have, Chumash Ethnobotany: Plant Knowledge Among the Chumash People of Southern California by Jan Timbrook. If anyone is interested in this sort of thing I'd be happy to post a summary of the information in there.

So far under "Indian Tobacco" I understood Lobelia. Nice to discover that also other tobacco inherited same common "Indian Tobacco" name. Thanks.

Alkaloid content and relative percentages of the purified alkaloid fraction:

Nicotiana tabacum
Alkaloids 11.462 mg/g
Nicotine 94.8%
Nornicotine 3.0%
Anabasine 0.3%
Anatabine 1.9%

Nicotiana attenuata
Alkaloids 22.269 mg/g
Nicotine 98.4%
Nornicotine 0.8%
Anabasine nil
Anatabine 0.8%

Nicotiana quadrivalvis
Alkaloids 7.76 mg/g
Nicotine 94%
Nornicotine ?
Anabasine ?
Anatabine ?

Nicotiana clevelandii
Alkaloids 8.945 mg/g
Nicotine 98.5%
Nornicotine 0.3%
Anabasine nil
Anatabine 1.2%

You can plug the names into This Database to see how various tribes used these species.

Maybe unrelated to this thread, but I've wondered about this for some time:

Do all plants from nightshade family contain nicotine?

Yes.. as well as atropine, scopolamine etc. The quantity of alkaloids vary in all nightshade plants alike. For example, bell peppers, potatoes, ashwahgandha etc.. have incredibly low levels of these compounds as they are hardly detectable. It's plants like belladonna, thorn apple, brugmansia etc.. that have very potent levels of these tropanes. However, nicotine is only concentrated within nicotiana plants.. and even some types of trees, afaik.

About how much tropane alkaloids are present in Nicotiana? Do tropanes play a significant part in the effects of a visionary dose of tabacum or rustica?

That I'm unsure of.. you'd want to be more concerned with the amount of nicotine and its derivatives, though. One does not need substantial amounts of tobacco to increase visionary thought.