Aerial photography indicated that Justicia americana is confined to the hardwater section of the New River. This species was determined to be moderately calciphilous based on average conductivity and hardness ratio of the water it inhabited. Productivity and standing crop averaged 23.3 g ash free dry weight (AFDW) m-2 d-1 and 2524 g AFDW m-2, respectively. Productivity of J. americana was 4-5 times greater than other major aquatic species in the New River and, in spite of its limited distribution, contributed 12% of the total aquatic macrophyte organic matter input to the river.