Common Reed - Phragmites communis
This member of the grass family (Poaceae) grows along the borders of brackish marshes and ditches. Each thick stem is topped by a plume-shaped inflorescence made up of many fuzzy spikelets. Attached to the stems are long, blade-shaped leaves with parallel veins.
There are both native and non-native varieties of Phragmites that grow in the U.S., but the native strain is scarce in Massachusetts. The non-native Common Reed that you see here is invasive: it can grow to a height of 15 feet and form dense thickets that prevent intrusion by other wetland plants. While each plant can produce a large amount of seed, the species typically spreads by underground stems known as rhizomes. Flowering occurs from late June through October, and the dried out flowering stalks can persist through the following growing season.