Bryopsis maixma is a densely branched green alga. It grows as multiple feather-like fronds, 150-200 mm long, arising form a holdfast. with more and longer branchlets on the upper axes. It differs from the native B. hypnoides and B. plumosa, which have more laterally spreading branches. This seaweed blooms in the spring, grows more rapidly than native in summer. and appears to regrow after the winter. It attaches to solid substrates, but also grows in sandy areas. It was described from Japan and Korea. It has been identified by molecular methods from Virginia Beach, the Indian River estuary, Delaware, Long Island Sound (all collected in 1995), and the Netherlands (1996). It has also been collected from Oman, on the Arabian Gulf. Likely vectors include ballast water, hull fouling, and Pacific Oyster transplants. No impacts have been reported, but this species appears to be spreading in Long Island Sound,