This is a clump of Dahlia tubers that has been washed with a garden hose nozzle prior to winter storage. The previous spring, this was 1 potato-like tuber.
I allow them to dry and then pack them in slightly damp sawdust in a plastic 5-gallon bucket with no lid. This clump may yield a dozen tubers when it is divided next spring. The number of divisions is determined by the "Eye" sprouts. Each division should have at least one robust sprout at planting time, which is after the last frost. I remove any diseased or rotted tubers, and allow them to Sun-dry completely before adding them to my compost bin.