Ribbon Weed Adaptations

The name ribbon weed applies to plants in the genus Vallisneria. They grow on the bottom of ponds, rivers, ditches, streams and lakes. Leaves are flattened, between 3 to 20 feet long, and look like green ribbons extending in the direction the water is flowing. Flowers are specialized so pollination can occur even though plants are underwater. Ribbon weed plants have adapted to survive floods, droughts and brackish water. Different kinds of Vallisneria occur around the world. They are also known as tapegrass, eel grass or water celery.

  1. Leaves

    • Long, flat leaves have rounded tips that tend to float. This design allows the ribbon weed to have lots of surface area to conduct photosynthesis and exchange gases. Ribbon grass grows in thick patches, so the density of leaf growth helps stabilize the substrate the plants are growing on. This can lessen flood damage. Leaves trap water-borne sediments, helping to clean water. Sediments enrich underwater soils in sandy-bottomed streams. In Australia, plant density of ribbon weed in the Hawkesbury and Nepean Rivers was heavy enough so the plant could be harvested for cattle feed.

    Flowers

    • Ribbon grass has separate male and female plants. Pollination can't occur underwater, so specialized flowers are produced. Male-flowered plants have flower stalks tucked between leaf sheaths and the plant base. Tiny male flowers are released to float to the top of the water. Female plants produce flowers at the tips of long, coiled flower stalks that expand like a spring to hold the female flowers at the water surface, where they are pollinated by floating male flowers. After pollination, the coil tightens up to take the female flower back underwater. This protects the developing seed pod.

    Roots

    • Manatees graze on seagrasses like ribbon grass.
      Manatees graze on seagrasses like ribbon grass.

      Ribbon weeds have fibrous roots that anchor the plants in place in the muddy or sandy stream and river beds, where seasonal high water flows occur. Roots keep ribbon grass from being dislodged when water flows are deeper and faster. Plants can be at risk of being torn out when leaves are fed on by aquatic life such as manatees, large herbivorous mammals. Waterfowl are known to dig up the runners.

    Rhizomes and Runners

    • Enlarged food-storing rhizomes and elongated runners are contained in the root system. Ribbon grass can move into new areas by sending out shoots from runners and new leaves from rhizomes without having to rely on seeds to start new plants. If leaves are removed, such as in harvesting for cattle feed, reduced water flow during drought or by scouring during flooding, the rhizomes and runners remain in the stream bed to regrow and restore plant growth.

    Water Quality

    • Estuaries combine fresh water and sea water.
      Estuaries combine fresh water and sea water.

      Some kinds of ribbon grass can tolerate brackish water as well as fresh water. This makes it valuable in restoring estuarine or tidal communities -- where fresh water meets ocean water -- when submerged plant life has been depleted by excess algal growth or boat propeller damage. Ribbon grass acts as a pioneer plant in damaged areas of inlets and bays. Once ribbon grass is growing, it stabilizes the soil and gives a more sheltered habitat so other aquatic plants can get established. With plant life present again, fish, crustaceans, insects and other aquatic animal life have the cover and food they need to survive.

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References

  • Photo Credit Comstock Images/Comstock/Getty Images Karl Weatherly/Photodisc/Getty Images

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