Aquatic Plants of Pennsylvania. Timothy A. Block
aquatic plants. Many freshwater tidal marsh plants are classified as endangered, threatened, or rare by the Pennsylvania Natural Heritage Program, including water-hemp ragweed (Amaranthus cannabinus), swamp beggar-ticks (Bidens bidentoides), showy bur-marigold (Bidens laevis), American waterwort (Elatine americana), dwarf spike-rush (Eleocharis parvula), mud-plantain (Heteranthera multiflora), long-lobed arrowhead (Sagittaria calycina), subulate arrowhead (Sagittaria subulata), river bulrush (Schoenoplectus fluviatilis), Smith’s bulrush (Schoenoplectus smithii), Walter’s barnyard-grass (Echinochloa walteri), and wild-rice (Zizania aquatica).
Freshwater tidal marshes are an endangered habitat in Pennsylvania. They are limited to the narrow strip of Atlantic Coastal Plain in the state, and development of Philadelphia and the adjacent riverfront areas of Delaware and Bucks Counties has taken a heavy toll. Several plants that once grew along the tidal shores of the Delaware are believed to be extirpated. Parker’s pipewort (Eriocaulon parkeri), awl-shaped mudwort (Limosella australis), and Nuttall’s mud-flower (Micranthemum micranthemoides) have not been seen in Pennsylvania in over 50 years. Nuttall’s mud-flower is believed to be extinct throughout its range.
Threats to freshwater tidal marshes include riverbank erosion, leading to loss of fine sediments (Figure 1.13) and colonization by non-native, invasive plants. Common reed (Phragmites australis) is the most troublesome of the invaders. In addition, Chinese lobelia (Lobelia chinensis), a low-growing plant from the Asia-Pacific region, has also become common along the tidal shores of the Delaware River.
Figure 1.13. Tidal riverbank showing absence of fine sediments and tidal marsh vegetation except in the area protected by a discarded section of dredge pipe.
Sea level rise, which is already occurring, is another threat. To survive, tidal marshes will have to accrete (grow upward) due to the gradual increase in elevation brought on by sediment deposition, or migrate inland. However, rates of sediment deposition are too slow to keep up with the current increase in sea level, which is expected to be approximately one meter by the year 2100. Unfortunately, a recent study has revealed that in very few cases is land available for freshwater tidal marshes in Pennsylvania to migrate inland (Titus et al. 2009).
MANAGEMENT OF AQUATIC ECOSYSTEMS
Endangered, Threatened, and Rare Species
About 60 species of aquatic plants are classified as endangered, threatened, rare, undetermined (candidate), or watch list by the Pennsylvania Natural Heritage Program at this time (PNHP 2010). One species, northeastern bulrush (Scirpus ancistrochaetus), is also listed as threatened under the Federal Endangered Species Act (Figure 1.14; Table 1.2).
Because of their rarity, these plants make an important contribution to the overall biological diversity of aquatic ecosystems. Many, such as water lobelia (Lobelia dortmanna), bayonet rush (Juncus militaris), floating-heart (Nymphoides cordata), slender water-milfoil (Myriophyllum tenellum), and horned bladderwort (Utricularia cornuta) are associated with oligotrophic glacial lakes; Pennsylvania populations represent the southern limit of range of these species.
An 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 |
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Brazilian waterweed
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