Hydrilla vs. Eurasian milfoil vs. eelgrass: how to tell submerged plants apart
Three submerged plants that look superficially similar from a dock and require completely different treatment. Misidentifying one for another either kills native fish habitat or leaves the invasive untouched.
| Attribute | Hydrilla verticillata | Myriophyllum spicatum | Vallisneria americana |
|---|---|---|---|
| Status | Federal noxious weed; invasive | Invasive (non-federal in most states) | Native — protect, don't treat |
| Leaf arrangement | Whorls of 3–8 around the stem | Whorls of 4 around the stem | Single rosette base, no whorls |
| Leaf edges | Sandpaper-rough, visible teeth | Smooth (feathery) | Smooth (slick to the touch) |
| Diagnostic feature | Tubers on the roots | 12+ pairs of thread-like leaflets per leaf | Flat ribbon-like leaves from a single base |
| Roots | Rooted, with white tubers | Rooted, no tubers | Rooted rhizome, no tubers |
| Growth rate | 1–4 inches/day; reaches surface from 25 ft | 1–2 inches/day stem extension | Slow; tops out at the surface, no dense mat |
| Reproduces by | Fragments, tubers, turions | Fragmentation (high) and seed | Rhizome runners and seed |
| Range | Southeast US, California, Pacific NW, expanding north | Northern US lakes, Great Lakes, Pacific NW, Northeast | Eastern and central US, freshwater bays and lakes |
| Treatment | Mechanical harvest + fluridone or endothall + grass carp | Triclopyr, fluridone, hand-pulling, drawdown | None — primary fish habitat |
| Common confusion | Often mistaken for native eelgrass | Native northern milfoil (5–10 leaflet pairs) | Often killed accidentally by hydrilla treatment |
Frequently asked questions
How do I quickly tell hydrilla from eelgrass?
Pull a sample from 3–4 ft of water. Hydrilla has whorls of 3–8 leaves around the stem with sandpaper-rough edges. Eelgrass has flat ribbon leaves from a single base with smooth edges. If you see whorls, it's an invasive.
Is Eurasian milfoil worse than hydrilla?
Different problem. Hydrilla is harder to eradicate (tuber bank survives 4+ years). Milfoil spreads faster between water bodies via fragments on boats. Both top out and form dense surface canopies that kill native vegetation.
Will fluridone hurt my eelgrass?
Yes, at typical hydrilla treatment rates. Mechanical harvesting is the only method that selectively removes hydrilla while preserving eelgrass beds.
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- Hydrilla vs. native eelgrass: how to tell them apartNative eelgrass is fish habitat. Hydrilla is an invasive that smothers it. Here's how to identify what's in your water before you start treatment.
- Aquatic invasive weeds in the United States: identification guideNine invasive aquatic plants cause the majority of waterway damage across the United States. Here's how to identify each one before treatment.