I am interested in knowing what is a known close relative to citrus, that is known to grow in the northeast US, such as western New York. Does anyone have any recommendations?
The coldest area in western New York gets down to about -25° Fahrenheit, so no true citrus will survive. The closest you'll get is Trifoliate Orange, Poncirus trifoliata. This plant can inter-graft and hybridize with Citrus species, but is inedibly bitter. It is an extremely thorny plant. It's leaves are compound and deciduous. It is hardy to -22° Fahrenheit. They can get up to about 25 feet tall in warmer areas, up to 8-10 feet in the coldest parts of it's range.