Submerged Aquatic Vegetation (SAV) Identification Key

​​The bay grass key was designed to allow you to identify most species of bay grasses found in Maryland. Although bay grasses are notoriously difficult to identify using standard taxonomic keys, the flexible format of the Internet allows us to combine detailed pictures, simple line drawings and text messages in a stepwise sequence that makes identifying bay grasses simple. You may find it useful to have a clear metric ruler with millimeters marked, a magnifying glass, and a Ziploc plastic bag to help you in the process of identifying your plant.

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Common Name:  
Scientific Name:

Common Name:Widgeon Grass

Scientific Name:Ruppia maritima

Native or Non-native:Native

Illustration:Widgeon Grass collage

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Widgeon grass tolerates a wide range of salinity, from the slightly brackish upper and mid-Bay tributaries through near-seawater salinity in the lower Bay and even in hypersaline salt pannes. Widgeon grass has also been reported to grow in the freshwater parts of some estuaries and in non-tidal waters. In more saline lower Chesapeake Bay , widgeon grass is by far the dominant bay grass. Widgeon grass is most common in areas with sandy substrates, although it occasionally grows on soft, muddy sediments. High wave action can damage the slender stems and leaves of widgeon grass.

Short, ​Linear, thread-like leaves are 3 to 10 cm (1 ¼ in to 4 in) long and 0.5 mm (<1/32 in) wide. Leaves are arranged alternately along slender, branching stems. Leaves have a sheath at the base and a rounded tip. Widgeon grass has an extensive root system of branched, creeping rhizomes that lack tubers. There are two growth forms of widgeon grass in Chesapeake Bay: an upright, highly branched form present during flowering (summer); and a creeping growth form with the leaves appearing basal from early spring through later winter.

Ecological Significance:
Widgeon grass populations tend to fluctuate significantly from year to year. Multi-acre beds often appear one year and disappear the next. Within the growing season, widgeon grass also grows and dies back quickly compared to other species- often appearing in May and being nearly completely gone by the end of August. Despite it's ephemeral nature, Widgeon grass is one of the more valuable waterfowl food sources for waterfowl and all parts of the plant have excellent nutritional value. Widgeon grass is also important for its ability to tolerate a wide range of salinity. In higher salinity water, widgeon grass is often found growing together with eelgrass, with the widgeon grass more common in shallow areas and the eelgrass more common in deeper water. Widgeon grass can also be found growing in ditches alongside roads and agricultural fields where it derives its other common name, ditch grass. Widgeon grass is an important and easily accessible habitat for many micro and macro invertebrates and some small fish.

Similar Species:
​ When not in flower or with seeds, widgeon grass closely resembles horned pondweed (Zannichellia palustris) and sago pondweed (Stuckenia pectinata). Unlike widgeon grass, however, horned pondweed has opposite to whorled leaves, and the leaves of sago pondweed are in bushy clusters. When in seed, the single seed pods that form at the base of fan-shaped clusters of short stalks distinguish widgeon grass. Sago pondweed seeds are in terminal clusters, and horned pondweed seeds occur in groups of 2-4, are horn-shaped and form in the leaf axils.

​ Widgeon grass reproduces asexually and sexually. Asexual reproduction occurs by emergence of new stems from the root-rhizome system. Sexual reproduction in late-summer produces two perfect flowers enclosed in a basal sheath of leaves. The flowers extend towards the water surface on a peduncle or flower stalk. Pollen released from stamen float on the water surface until contacting one of the extended pistils. Fertilized flowers produce four black, oval-shaped fruits with pointed tips. Individual fruits extend on stalks, which occur in clusters of eight stalks.

Print out a complete version of the key in PDF format (Adobe Acrobat file 18MB)

For permission to reproduce individual photos, please contact Mike Naylor

The text and photos used in this key were produced through a collaborative effort among the following partners.

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