Deep, dark, double purple-black flowers on tall stems are not always recognized as a columbine at first glance. Plant it against a lighter background so they can really show off, otherwise, they might visually disappear and you wouldn't want such a wonderful columbine to go unnoticed. Short-lived but will reseed prolifically.
Mature size: 1-3 feet tall (including flowers spikes) & 1-2 feet wide
Minimum temperature: -30° F