"The term spice means any aromatic vegetable substance in the whole, broken, or ground form, except for those substances which have been traditionally regarded as foods, such as onions, garlic and celery; whose significant function in food is seasoning rather than nutritional; that is true to name; and from which no portion of any volatile oil or other flavoring principle has been removed. Spices include the spices listed in Sec. 182.10 and part 184 of this chapter...."
As I interpret this, together 21 C.F.R. § 182.10 and 21 C.F.R. § 184 comprise the official list of what may be labeled as "spices". The first is the list of things normal people would recognize as spices, and contains a few nightshades; the second has some truly bizarre stuff in it, but no nightshades. The items relevant to us are these:
Capsicum - - - - - - - Capsicum frutescens L. or Capsicum annuum L.
Cayenne pepper - - - Capsicum frutescens L. or Capsicum annuum L.
Paprika - - - - - - - - - Capsicum annuum L.
('L.' just means that it was named by Linnaeus.)
So, the moral here is that peppers are a problem, but in the US "spices" never means tomatoes, potatoes, or eggplants.
I've never heard of anyone allergic to some peppers but not others -- have any of you? Are pepper species something we should be carefully breaking out?
Next up: "Natural flavorings", which is much harder to go through exhaustively.