Based on taxonomic keys neither barbatum or callosum should have warts on the lower edge of the petals. And in general barbatum has less warts on the petals than callosum. Of the three close taxa; barbatum, callosum, and lawrencianum, only lawrencianum should have warts on the lower edge of the petals.
The staminodes of lawrencianum and barbatum are more similar than to callosum, and should have a prominent projection pointing down on the lower edge near the center of the notch.
That being said, the range of collosum var. sublaeve is contiguous with barbatum, and there are intergrades of the two where the range overlaps. That's probably a good indication that barbatum is probably just another variety of callosum. Maybe someday they will do some DNA work to find out how far apart they really are.