D. filiformis filiformis is a northern plant, mainly growing from about North Carolina to Nova Scotia. It also stay generally smaller, to about 6 inches high, and with deeper red colors. There are exceptions, such as the Giant form in Florida, and the Florida All Red which is a fully subtropical form, needing no dormancy.
D. filiformis tracyi (or D. tracyi if you believe it's a separate species, I haven't seen enough difference yet to warrant this) is a much larger southern plant, growing along the gulf coast into Florida and Georgia, and reaching up to 20 inches high or more. It tends to be nearly all green, with only a tint of pink to the tentacles, and usually shorter, but denser tentacles on the leaves as well.