Submerged Aquatic Vegetation (SAV) Identification Key
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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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If you already know the identity of a particular bay grass use the drop down boxes below. |
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Common Name:
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Scientific Name:
| | Common Name: | Horned Pondweed |
| | Scientific Name: | Zannichellia palustris
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| | Native or Non-native: | Native
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| | Illustration: | 
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| | Family: | Zannichelliaceae |
| | Distribution: | Zannichellia palustris or horned pondweed is found in every state in the continental United States, as well as in Europe and South America. Horned pondweed is widely distributed in Chesapeake Bay, growing in fresh to moderately brackish waters, in muddy and sandy sediments. Horned pondweed seems to grow most abundantly in very shallow water but may grow to depths of 5m (16.4 ft) given enough light. Horned pondweed is an annual plant and is one of the first bay grasses to appear in the early spring. By June as water temperatures warm, the plants release their seeds and die back. Two growth forms of horned pondweed are found in the bay, one upright and the other creeping, the latter of which is found in areas of higher wave energy. |
| | Recognition: | Long, linear, thread-like leaves are mostly opposite or arranged in whorls on slender branching stems. Leaf tips gradually taper to a point, and a thin sheath or stipule covers the basal parts of leaves. Horned pondweed has tendril-like roots and slender rhizomes. The seeds of horned pondweed readily distinguish this species and occur in groups of 2 to 4, are horned shaped and form in the leaf axils. |
| | Ecological Significance: | Horned pondweed provides food and habitat for many species of macro and micro-invertebrates, and these species are in turn eaten by species of fish, amphibians, waterfowl, etc. Waterfowl also commonly eat the plant and its seeds. Horned pondweed may have unique value to some organisms as it is present much earlier in the year than most other species. |
| | Similar Species: | Sago pondweed ( Stuckenia pectinata) and widgeon grass ( Ruppia maritima) are similar in appearance to horned pondweed. Sago pondweed, however, has leaves in bushy clusters, and widgeon grass has alternate leaves, whereas horned pondweed has opposite or whorled leaves. The species are easily distinguished when they are in seed. Widgeon grass has single seed pods that form at the base of fan-shaped clusters of short flowering stalks. Sago pondweed seeds are in terminal clusters. Horned pondweed has distinctively (horned) shaped seeds that occur in the leaf axils in groups of 2 to 4. By the time sago pondweed and widgeon grass appear horned pondweed usually is covered with seeds. |
| | Reproduction: |
Two growth forms of horned pondweed occur in Chesapeake Bay: an upright form with free-floating branches, and a prostrate or creeping growth form with stem node roots that anchor the plant in areas with high wave energy (also common form in winter). Horned pondweed is usually the first bay grass to appear in spring, and seed formation occurs in early to late spring. Reproduction is mostly by seed formation; the seeds are horn-like, slightly curved fruits that occur in groups of 2 to 4. Decline usually begins in June or early July, and produces floating mats of decaying plants. Thereafter, a second growth cycle can occur in fall, and it can grow over the winter in some areas. Horned pondweed seeds generally germinate in the same year as seeds are set. |
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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.
