Fortunately, the differences between the two subspecies are fairly reliable. I recommend using the following characters.
1)The outer surface of the pitcher of the northern subspecies is smooth, glossy, and waxy, while the outer pitcher surface of the southern subspecies is rough or pubescent.
2)The hood of the northern plant tends to be smaller, and if pinched together the lateral ears barely touch, while the lateral ears usually overlap readily in the southern plant.
3)The northern species has pitchers which are overall 3 × longer than the width of the pitcher mouth; the southern pitchers are not so elongate.
4)The flowers of the northern subspecies are a darker red or purple.
You can often find individual plants that violate one or more of these characters; you must identify plants using several specimens. Think "population level"! Incidentally, not everyone is quite sure that it is correct to use the subspecies names at all. Recent research on climate variations across the continent suggest that the two subspecies may actually just be the result of climate gradients. Is it possible they will find evidence suggesting that McDaniel (as described below) was right after all, and that the subspecies should be united? Meanwhile, at least one naturalist has noted in on-line, unpublished musings that the northern plants should be divided into a coastal entity and an inland entity of as-yet unspecified rank. Would such musings bear the scrutiny of a refereed peer review process?