Survey of Aquatic Vascular Plants

For the past four years, with funding from the Pennsylvania Wild Resources Conservation Fund, we have been conducting surveys of aquatic vascular plants on lakes in eastern Pennsylvania. To date we have surveyed 92 lakes with the following results.

Most common native aquatic species and the number of lakes in which they were found
Nuphar variegata 66
Potamogeton epihydrus 60
Sparganium americanum 57
Nymphaea odorata 53
Brasenia schreberi 47
Dulichium arundinaceum 44
Utricularia macrorhiza 43
Pontederia cordata 42
Eleocharis palustris 41
Sagittaria latifolia 37
Najas flexilis 34
Decodon verticillata 34
Elodea nuttallii 33

Invasive, non-native plants and the number of lakes in which they were found
Potamogeton crispus 14
Elatine triandra 11
Myriophyllum spicatum 10
Nymphaea pink-flowered 9
Lythrum salicaria 9
Phragmites australis 5
Polygonum cuspidatum 4
Trapa natans 3
Cabomba caroliniana 3
Hydrilla verticillata 1

As a result of our surveys we have recommended that the following species be dropped from the state lists of endangered, threatened, and rare species, as they are more abundant than was previously realized.

Eleocharis olivacea
Glyceria borealis
Gentiana linearis
Najas gracillima
Orontium aquaticum
Polygonum aquaticum var. stipulaceum
Potamogeton bicupulatus
Potamogeton robbinsii
Utricularia geminiscapa
Utricularia purpurea
Wolffia borealis
Xyris montana


Other Findings
Long-stem waterwort (Elatine triandra) - We have continued to discover additional populations of a species of Elatine (waterwort) that we initially identified as American waterwort (E. americana). However, in Pennsylvania, American waterwort has traditionally been limited to the intertidal areas of the Delaware River, where it has not been collected for more than 50 years (Rhoads and Klein 1993). After finding this species at several very degraded lakes in southeastern Pennsylvania this year, we checked further into its identification and have concluded that the specimens in question are long-stem waterwort (Elatine triandra), a species not previously recorded for Pennsylvania. Gordon Tucker, who is preparing the treatment of the Elatinaceae for Flora North America, has confirmed that our specimens are E. triandra.

Elatine triandra is native to Eurasia and western North America. It has been collected in Maine, where it is considered to be introduced (Haines and Vining 1998; Tucker 1986), and recently at several locations in New York (G. Tucker, personal communication). Taxonomic confusion has further obscured the true identity of the waterworts. American waterwort was considered to be a variety of E. triandra; Gleason and Cronquist (1991) list it as Elatine triandra Schkuhr var. americana (Pursh) Fassett, whereas E. triandra is Elatine triandra Schkuhr var. triandra. Other authors (Tucker 1986; Crow and Hellquist 2000) recognize both American and long-stem waterwort at the species level as Elatine americana (Pursh) Arn. and E. triandra Schkuhr respectively.

We have concluded that the plant we initially collected as Elatine americana at eight lakes in Luzerne, Pike, Susquehanna, and Berks Counties is, in fact, E. triandra, and that this species is apparently spreading rapidly within our range. Inspection of herbarium specimens at the Academy of Natural Sciences of Philadelphia indicates that E. triandra is also present at one additional lake in Pike County, and that it has been at Twin Lakes in Pike County since at least 1960.

Inflated bladderwort (Utricularia inflata) - Inflated bladderwort is another plant that shows very aggressive tendencies. This species was first collected in Pennsylvania at three sites in Sullivan County 1993-1997, but recorded at the time as U. radiata, a similar but smaller plant, which had previously been considered a variety of U. inflata. However, Peter Taylor in his monograph on the genus Utricularia (Taylor 1989) recognized both taxa at species rank as did Crow and Hellquist (2000). It has now been found by us at eight lakes in northeastern Pennsylvania and is undoubtedly present at others.

Inflated bladderwort is native to the coastal plain from Delaware to Florida and Texas (Gleason and Cronquist 1991); we probably will never know exactly how it became established in Pennsylvania. It is also known from a single site in New York (Mitchell et al. 1994) and one in Massachusetts (Sorrie 1992).

Following our recognition of its presence at Pecks Pond and Tobyhanna Lake in 2000, it was added to the Pennsylvania Natural Heritage Program plant list with a TU (tentatively undetermined) classification. However, it appears to be spreading even to lakes that are not visited by boaters such as Beech Lake in State Game Lands 57; waterfowl may be the vector.

Like purple bladderwort, inflated bladderwort can become very abundant locally, causing distress to various recreational users. It is frequently present in vegetative condition only; we have learned to recognize it in the absence of flowering stems based on leaf and stem tip characteristics. Utricularia inflata has a G5 (globally secure) rating overall; it is S1 (critically imperiled) in MI, NY, NJ, DE, MD, TN, AL, and OK. It is rated as S2 (imperiled) in VA and NC. It is considered invasive in Washington State, the only western state in which it has been found (NatureServe 2004; Washington State Department of Ecology 2004).

Broad-leaved water-milfoil (Myriophyllum heterophyllum) - We have previously (Rhoads and Block 2001) reported on large populations of Myriophyllum heterophyllum (broad-leaved water-milfoil) that are present at several eastern Pennsylvania lakes. During our 2003 surveys we documented two additional occurrences of this aggressive species and noted the expansion of one previously recorded occurrence.

At Harris Pond in Luzerne County, a PA Fish and Boat Commission lake, Myriophyllum heterophyllum dominated the entire lake. It was rooted throughout, except in the deepest central region; in addition, floating fragments covered the water surface in the vicinity of the dam and extending for about one-third the length of the lake.

We documented an additional population in the inlet at Harvey’s Lake, where the presence of this species was first noted by A. E. Schuyler in 1982. Interestingly, we did not see this species anywhere else in this large lake although it is abundant in the inlet. A revisit to Lily Lake, another PA Fish and Boat Commission site in Luzerne County, revealed a dramatic expansion in the area occupied by Myriophyllum heterophyllum compared to our previous visit in 2001.

Myriophyllum heterophyllum is classified as G5 (globally secure); in 6 states or provinces it is classified as S1 (critically imperiled): New Brunswick, IA, OH, PA, MD, DE. It has S2 (imperiled) status in Quebec, NJ, KY, and NC. It is considered secure in Ontario and VA. Vermont, Hew Hampshire, New York, Rhode Island, and the District of Columbia consider Myriophyllum heterophyllum to be exotic (NatureServe 2004; New Hampshire Department of Environmental Services. 1999).

Crow, Garrett E. and C. Barre Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America. The University of Wisconsin Press, Madison

Haines, Arthur and Thomas F. Vining. 1998. Flora of Maine, a Manual for Identification of Native and Naturalized Vascular Plants of Maine. V. F. Thomas Co., Bar Harbor, ME.

Mitchell, Richard S., Terryanne E. Maenza-Gmelch, and J. G. Barbour. 1994. Utricularia inflata Walt. (Lentibulariaceae) new to New York State. Bull. Torrey Botanical Club 121(3): 295-297.

NatureServe Explorer http://www.natureserve.org/explorer/ accessed 1/16/2004.

Rhoads, A. F. and W. M. Klein. 1993. The Vascular Flora of Pennsylvania: Annotated Checklist and Atlas. American Philosophical Society, Philadelphia, PA

Sorrie, Bruce A. 1992. Utricularia inflata Walter (Lentibulariaceae) in Massachusetts. Rhodora 94: 391-392.

Taylor, P. 1989. The Genus Utricularia – A Taxonomic Monograph. Royal Botanic Gardens Kew, London

Tucker, Gordon C. 1986. Genera of Elatinaceae in the southeastern United States. Journal of the Arnold Arboretum 67(4): 471-483.

Washington State Department of Ecology, http://www.ecy.wa.gov/programs/wq/plants/weeds/bladder.html, accessed 1/26/2004.

Brasenia schreberi - Water-shield

Decodon verticillatus - Water-willow, at edge of lake

Isoetes echinospora - Quillwort

Lobelia dortmanna - Water lobelia, an endangered species in Pennsylvania

Pecks Pond - Pike County

Utricularia inflata - Inflated bladderwort

Polygonum amphibium var. stipulaceum - Water smartweed

Potamogeton epihydrus - Ribbonleaf pondweed