additional twelve species are believed to be extirpated in Pennsylvania. Of these, four are plants that were found in the freshwater intertidal zone.
PNHP-listed plants are protected under the Pennsylvania Code, Title 17, Chapter 45, Conservation of Pennsylvania Wild Plants and implementing regulations (Commonwealth of Pennsylvania 1993). The program is administered by the Pennsylvania Natural Heritage Program and the Bureau of Forestry of the Department of Conservation and Natural Resources.
Figure 1.14. Northeastern bulrush (Scirpus ancistrochaetus), a federally threatened aquatic plant that occurs in Pennsylvania.
Table 1.2. Endangered, Threatened, and Rare Aquatic Plants of Pennsylvania
a Global ranks: G5 = secure, G4 = apparently secure, G3 = vulnerable; state ranks: S3 = vulnerable, S2 = imperiled, S1 = critically imperiled, SU = status uncertain, SX = apparently extirpated.
b PNHP status: PE = Pennsylvania endangered, PT = Pennsylvania threatened, PR = Pennsylvania rare, PX = extirpated in Pennsylvania, TU = tentatively undetermined, N = not listed, SP = special population, W = watch list.
c Federal rank: LT = listed threatened.
Problem Vegetation
Exotic invasive species—Non-native plants have invaded aquatic ecosystems as well as terrestrial habitats (Table 1.3). In low nutrient systems they are usually not a problem, as most serious invasives require high resource availability to grow vigorously. Where nutrients are not limiting, species like European water-chestnut (Trapa natans) (Figure 1.15), Eurasian water-milfoil (Myriophyllum spicatum), hydrilla (Hydrilla verticillata), fanwort (Cabomba caroliniana), or curly pondweed (Potamogeton crispus) can become dominant. Invasive species are also more likely to become a problem in recently created impoundments where a native flora has not yet become established, or in lakes where excessive use of herbicides has eliminated the native plants. Dense growth of species like water-chestnut or Eurasian water-milfoil not only interferes with native plant growth, but also interferes with recreational uses such as boating and swimming.
Table 1.3. Non-native, Invasive Aquatic Plants in Pennsylvania
| COMMON NAME | SCIENTIFIC NAME | % OF LAKESa |
| long-stem waterwort | Elatine triandra | 15.7 |
| curly pondweed | Potamogeton crispus | 13.0 |
| Eurasian water-milfoil | Myriophyllum spicatum | 9.6 |
| cultivated water-lilies | Nymphaea spp. | 9.6 |
| yellow iris | Iris pseudacorus | 4.3 |
| water-chestnut | Trapa natans | 3.5 |
| hydrilla | Hydrilla verticillata | 3.0 |
| fanwort | Cabomba caroliniana | 2.6 |
| waternymph | Najas minor | 1.8 |
| Brazilian waterweed | Egeria densa | <1.0 |
| European water-clover | Marsilea quadrifolia | <1.0 |
| flowering-rush | Butomus umbellatus | <1.0 |
| mudmat | Glossostigma cleistanthum | <1.0 |
| parrot-feather | Myriophyllum aquaticum | <1.0 |
| watercress | Nasturtium officinale | streams and springs |
| water-starwort | Callitriche stagnalis | streams and springs |
a Based on surveys of 115 lakes between 2000 and 2007.
Prevention is far more effective than attempts to control an invasive plant after it has become established. Prevention can take the form of limiting access by boats from other areas that might carry seeds or plant fragments and educating lake users to prevent deliberate or accidental introductions of non-native plants. Another approach is to protect water quality; nutrient enrichment (eutrophication) will exacerbate problems with over-abundant vegetation.
Figure 1.15. An infestation of the non-native, invasive water-chestnut (Trapa natans) at a lake in Bucks County, PA.
Physical control efforts such as pulling, cutting, or raking may provide temporary relief; however, the ability of many aquatic plants to propagate themselves from detached fragments should be kept in mind.
Over-abundant native species—Not all problems arising from excessive growth of aquatic vegetation are caused by non-native species. Under favorable growing conditions some native species can also form dense stands that interfere with recreational uses of lakes. Shallow water and high nutrient availability are most often the causes.
Opportunistic species that have created problems include fragrant waterlily (Nymphaea odorata) (Figure 1.16), Farwell’s water-milfoil (Myriophyllum farwellii), common water-milfoil (M. humile), broad-leaved water-milfoil (M. heterophyllum), waterweed (Elodea nuttallii), purple bladderwort (Utricularia purpurea), inflated bladderwort (Utricularia inflata), and coontail (Ceratophyllum demersum).
Prevention of problems caused by explosive growth of native species should focus on reducing nutrient inputs.
Figure 1.16. Water surface nearly covered by native fragrant water-lily (Nymphaea odorata)
