Ponderosa lemon
The ponderosa lemon originated in roughly 1887, and is believed to come from a chance seedling grown in Hagerstown, Maryland. It was later named and introduced to the nursery trade in 1900. Though often referred to as a cross between the lemon and citron, a recent genomic analysis showed it to solely contain pomelo ("Citrus maxima") and citron ("Citrus medica") DNA, perhaps being an F2 hybrid. Thus they cannot derive from true lemons, which have a mandarin orange component.
Buddha's hand
The different cultivars and variations of this citron variety form a gradient from "open-hand" types with outward-splayed segments to "closed-hand" types, in which the fingers are kept together. There are also half-fingered fruits, in which the basal side is united and the apical side fingered. The origin of this kind of citron is commonly traced back to the Far East, probably northeastern India or China, where most domesticated citrus fruits originate.