Delicious Marion blackberry jam seedless perfect on toast makes a great PB&J Marrionberries are the King of blackberries. There are many different varieties of blackberries, but the Marions are considered the premium variety of the blackberry family. They have a deeper, richer, rounder flavor than regular blackberries. They don't have the slight bitter edge that people often associate with blackberries. Of all the berries, Marionberries have the most 'berry-ish' flavor. If you are a blackberry lover, then you certainly do not want to miss out on this special treat. Pioneer Valley perfectly captures the essence of Marion blackberries in the wonderful jam. Seedless for those people who find the seeds annoying or pesky.