1. Corolla blue; calyx 1.8-2.7 mm long (to 3 mm in fruit); stem leafy only on lower portion, with inflorescence(s) entirely above uppermost leaves and bracts; style shorter than mature nutlets, inconspicuous; nutlets convex on exposed surface, 4-5.5 mm long, without rim.

C. boreale

1. Corolla dull red or maroon (to purplish); calyx 4-6.5 mm long; stem leafy its entire length, with branches of the inflorescence arising from axils of leafy bracts; style conspicuously surpassing mature nutlets; nutlets flat on exposed surface, 5.5-8 (-9) mm long (including prickles), with raised rim on border.

C. officinale