Cynoglossum

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

All species found in Cynoglossum

Cynoglossum borealeNORTHERN WILD COMFREY 
Cynoglossum officinaleHOUND'S-TONGUE 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. June 26, 2017. http://michiganflora.net/genus.aspx?id=Cynoglossum.