Sanguisorba canadensis (American/Canadian burnet)

American or Canadian burnet is a wetland wildflower that is known for its prolific bottlebrush-like white flowers that bloom from June through October on dense, erect, cylindrical spikes. Thrives in sun and in soils that keep its roots damp. Grows to 2-6' tall, depending on conditions. Can spread through rhizomatous roots. An underappreciated plant that offers stunning color and interest in fall. 

American or Canadian burnet is native to much of the northeastern and northwestern coasts of North America. It is found in swamps and bogs, but is now listed as threatened or endangered in much of its native range due to habitat loss. In Maryland, it is listed as "threatened." A big attractor of pollinators, it produces large amounts of pollen and nectar in late fall, when pollinators need food to successfully overwinter. 

BONAP Native Range Map (bright green indicates county native, dark green indicates state native).

Photo from Plant Identifier