Bill's Botanical Forays

Is this Rubus trivalis?

Today, this plant was discovered on the North Tract of the Patuxent Research Refuge, in a wet area alongside the road. The prickles on the stems were not as robust as those on Rubus flagellaris observed elsewhere. However, it does have a single flower from each node, unlike Rubus hispidus. So, it could be something new, or simply a variation of Rubus flagellaris. Considering that R. trivalis has been reported as far north as Pennsylvania, it is a possibility. Is there an additional trait I should look for to make a more definitive identification?