Spiked Blackberry-Marjoram Limeade

Puree blackberries, lime juice, vodka, sugar, and marjoram in a blender. Strain through a fine-mesh sieve, pressing on solids with a flexible spatula; discard solids. Puree can be made ahead and refrigerated in an airtight container up to 2 days.

Divide puree among 8 ice-filled glasses. Fill with seltzer; stir. Serve, garnished with blackberries, lime wedges, and marjoram.