cream of tartar (potassium bitartrate) is plant based, i wonder if it would serve as a good potassium supplement? i found this explanantion for its origins online
"Cream of tartar is a by-product of the wine industry. A crystalline acid forms on the inside of wine barrels. The barrels are scraped and the sediment is purified and ground to form cream of tartar. Cream of tartar is used to stabilize egg whites when making meringue or as an addition to certain frostings to produce a creamy product."
also see here, where it is described as an "acid salt" which apparently means it is an acid that is partially nuetralized by being bound to a mineral, in this case the mineral is potassium.