Identifying Coontail (Hornwort)
Coontail (Ceratophyllum demersum) is a distinctive submerged aquatic plant that is not difficult to identify once you know its key features. The most important identification skills are: (1) recognizing coontail's unique leaf structure (forked, stiff, and somewhat scratchy), and (2) distinguishing it from hydrilla (Hydrilla verticillata), which occupies similar habitats and is frequently misidentified as coontail by people unfamiliar with both species. This distinction is critical because hydrilla is an invasive species requiring management action, while coontail is a native species that typically does not.
Key Identification Features
1. Forked (Bifurcated) Leaves
The most distinctive feature of coontail is its leaves. Each leaf is repeatedly forked (dichotomously branched) into progressively narrower segments, with the finest segments being rigid, spiny, and sharply pointed. The overall leaf shape resembles a fan or a tiny bottle brush segment. This forked leaf structure is unique among common submersed aquatic plants — no other species commonly encountered in U.S. fresh water has this combination of whorled arrangement and forked leaf segments.
2. Whorled Arrangement with Dense Crowding Near Stem Tips
Coontail leaves are arranged in whorls (rings) around the stem, typically 6–12 leaves per whorl. Unlike hydrilla whorls (which are more evenly spaced along the stem), coontail whorls are densely packed toward the growing stem tips, creating a distinctive "bottle brush" or "raccoon tail" appearance — hence the common name. The tip of a coontail branch is distinctly bushy and bottlebrush-like, dramatically denser than the internodes toward the stem base.
3. Rough, Scratchy Texture
Coontail stems and leaves feel distinctly rough and scratchy when you run them through your fingers — more so than hydrilla, elodea, or milfoil. The roughness is caused by tiny teeth on the leaf segments. This tactile feature is a useful quick-check field test: a submerged plant that feels very scratchy throughout is almost certainly coontail.
4. No Roots
Pull a coontail plant from the water. Examine the base of the stems. There are no roots — no white thread-like root structures, no root crown, nothing anchored in the sediment. The stem base may be slightly paler than the upper stem but is otherwise bare. This rootless condition is unique to coontail among commonly encountered U.S. aquatic weeds (other submerged plants have roots). The absence of roots is immediately obvious when you collect a specimen — you will find nothing anchoring the plant in the sediment.
5. Stiff Stem Structure
Coontail stems are relatively stiff compared to hydrilla and milfoil stems. The coontail plant maintains a somewhat rigid form even when removed from water, while hydrilla and milfoil stems droop and collapse quickly without water support. This stiffness reflects coontail's lack of vascular tissue (it is a more primitive plant biologically).
6. Fruit (When Present)
In late summer, coontail produces small (3–5 mm), dark, nut-like fruits at the leaf axils. The fruit has two lateral spines and a persistent style (beak) at the tip. Fruit is produced infrequently compared to vegetative reproduction and is not present year-round, but when found, it provides definitive identification. The related spiny hornwort (Ceratophyllum echinatum) has fruits with longer, more prominent spines.
Comparison to Hydrilla
Coontail and hydrilla are the most commonly confused submerged aquatic plants in North American fresh water. Their confusion is understandable — both have whorled leaves and grow in the same lakes and rivers. However, they are easily separated by the following features:
| Feature | Coontail | Hydrilla |
|---|---|---|
| Leaf type | Forked, rigid segments | Simple blade, lance-shaped |
| Roots | None | White roots with tubers |
| Leaf margin | Entire segments with terminal spine | Distinctly serrated (toothed) edge |
| Stem tip appearance | Dense bottlebrush cluster | More open, evenly-spaced whorls |
| Midrib tooth | Absent | Present (feel it on underside) |
| Native status | Native to North America | Non-native invasive |
See the full coontail vs. hydrilla comparison for additional detail and management implications.
Seasonal Identification Notes
Coontail is recognizable year-round but presents slightly differently across seasons. In spring, newly growing coontail is bright green and the bottlebrush stem tips are most clearly defined — this is the easiest time for a beginner to identify the forked leaf structure. In summer, coontail in eutrophic lakes can form extremely dense beds; the upper stems maintain the characteristic dense leaf clusters while lower stems may be sparse or bare. In fall, as water temperatures drop, coontail senesces and older stems may become darker and more brittle. The rootless biology is diagnostic at all seasons — regardless of when you sample, pulling coontail from the water should yield no attached root structures. Fruit (when present in late summer) provides additional confirmation. Hydrilla, in contrast, can produce tubers year-round that remain in the sediment even when above-ground biomass is minimal — so tuber presence confirms hydrilla even when other vegetative features are less clear. If you are conducting plant surveys in fall or early spring when coontail biomass is low, always check for roots and confirm the forked leaf structure before recording identification.
References
- Les, D.H. (1988). The systematics and ecology of Ceratophyllum. Systematic Botany 13(3):359–388.
- UF/IFAS Center for Aquatic and Invasive Plants. plants.ifas.ufl.edu