Macrophytes consist principally of aquatic vascular flowering plants, but also include the aquatic mosses, liverworts, ferns, and the larger macroalgae. Like other primary producers, macrophytes respond to the quality of the water in which they grow. The use of biota, including macrophytes, is an increasingly important and recognized technique for assessing aquatic habitats.1–3 Macrophytes often constitute a dominant factor in the habitat of other aquatic organisms.
Freshwater macrophytes range in size from the tiny watermeal (Wolffia spp., see Section 10900, Plate 3A:D), about the size of a pinhead, to plants like the cattail (Typha spp., see Section 10900, Plate 3C:O), up to 4 m high. Higher aquatic plants often are abundant, occur clustered in high numbers, many in almost pure stands, covering extensive areas of shallow lakes, reservoirs, marshes, and canals. In marine water, intertidal rockweeds (Fucus spp., see Section 10900, Plate 2A:D, and Ascophyllum spp.) and offshore kelps (Fucus spp. and Macrocystis spp., see Section 10900, Plate 2A:E) are conspicuous. Vascular marine or estuarine plants, such as eelgrass (Zostera spp., see Section 10900, Plate 2B:N) and marsh grass (Spartina spp.), are essential to the aquatic ecosystem.