Here's the acid-alkaline range within a plant group according to Duncan and between groups [the brackets  () are all mine]:
[Plant remedies that] belonged to the same family — as, for instance, the Solanaceae — were connected by a rule of relationship, in regard to their polarity of action. Capsicum being the electro-negative [acid] extreme and Tabacum the positive [alkaline], the others standing in a regular order between. Among the Ranunculaceae the positive end is occupied by Helleborus [alkaline] the negative by Staphysagria [acid]. This I find holds good in every family of plants and in every family of chemical substances ; and we may from this conclude that the different plants also may be arranged in two classes according to their respective chemical constituents. There seems to be a correspondence between such families as are remarkable for containing acrid substances, as the Ranunculaceae and Euphorbiacese [acid], and the electro-negative chemicals, and between such families as contain bitter and narcotic substances and the electro-positive chemicals [alkaline].
-Duncan's "Acid and alkaline children"