I didn't post about it in the blog, Koen, because I didn't have time to look for good examples, but your suggestion of grain is completely possible.
Millet was in many of the old herbals, and was often drawn with extravagant seed heads compared to other grain drawings (especially the one they called Indian Millet). They weren't shaped like the VMS, but if the VMS drawing were saying, "This plant has tons of small round seeds at the top of a long stalk," then it would fit millet in a conceptual way. It wouldn't explain the hairy fringe around the perimeter, but I still wouldn't discount the possibility.
Millet was in many of the old herbals, and was often drawn with extravagant seed heads compared to other grain drawings (especially the one they called Indian Millet). They weren't shaped like the VMS, but if the VMS drawing were saying, "This plant has tons of small round seeds at the top of a long stalk," then it would fit millet in a conceptual way. It wouldn't explain the hairy fringe around the perimeter, but I still wouldn't discount the possibility.