The Potameton Species in Lake Runnemede
Summary of Current Research on Potamogeton Species in Lake Runnemede, 2021
There are three types of Potamogetons that currently live in Lake Runnemede: Hill’s Pondweed (Potamogeton hillii), Leafy Pondweed (Potamogeton foliosus) and a hybrid pondweed (Potamogeton zosteriformis X foliosus), which was formerly identified as Ogden’s Pondweed (Potamogeton x ogdenii).
The Paradise Park Commission established a dialogue with and hosted a visit by Dr. C. Barre Hellquist this summer regarding the health and welfare of the aquatic plants in Lake Runnemede. Dr. Hellquist is retired now but is considered one of the foremost experts in aquatic botany in the Northeast. It was his research that first identified the Ogden’s Pondweed in Lake Runnemede. During these discussions, Dr. Hellquist reported that recent research indicates that the plant in Lake Runnemede is not Ogden’s Pondweed, but instead a unique related hybrid found nowhere else in the world.
The taxonomy and systematics of the Pondweeds (Genus Potamogeton) has always been difficult. They exhibit a great deal of phenotypic plasticity (adaptation of a plant’s physical characteristics according to its environment) while adapting to their difficult aquatic habitats and some species rarely flower, preferring to reproduce vegetatively via rhizomes or winter buds. These adaptations also include genotypic variation (alterations to the plant’s genetic material) and exhibit a high degree of hybridization between species which has complicated the taxonomy even further.
One particular linear-leaved hybrid, Potamogeton x. longilingulatus, was identified during the 1930s, in various locations in the Northeast. During the 1980’s, Dr. Hellquist further classified this hybrid into two separate hybrids, Potamogeton ogdenii – a hybrid of P. zosteriformis X P. hillii, and Potamogeton haynesii – a hybrid of P. zosteriformis X P. strictifolius. P. ogdenii (Ogden’s Pondweed) was observed occasionally developing fruits, which led it to be reported as a new species, although it was actually a fertile hybrid. P. ogdenii and P. haynesii were distinct enough morphologically for the populations of each to be classified, including the population of P. ogdenii in Lake Runnemede.
Those classifications remained in place for 30+ years until the Czech botanist Zdenek Kaplan began working on developing a comprehensive treatment of the Genus worldwide. He refined DNA analysis techniques. In 2012, using plant materials provided by Dr. Hellquist, he determined that there were actually four hybrids with P. zosteriformis as the primary parent. Plants previously classified as P. ogdenii were further subdivided into three distinct hybrids, the original P. ogdenii, plus two unnamed hybrids: P. zosteriformis X P. berchtoldii and P. zosteriformis X P. foliosus. The first unnamed hybrid was determined to be the fertile hybrid previously described as P. ogdenii. The latter hybrid (the P. foliosus cross) was determined to be the plant in Lake Runnemede and it has not been identified in any other location worldwide.
The four P. zosteriformis hybrids are significant from an evolutionary biology perspective because they are aneuploid hybrids where the parent species have different numbers of chromosomes (P. zosteriformis has a chromosome number of 2n=28, while the other linear-leaved parents are 2n=26). The hybrids all have an intermediate chromosome number (2n=27) which makes them infertile. However, at some point in the distant past, early progenitors of the aquatic plants diverged into three separate genera within the family Potamogetonaceae apparently through modification of the chromosome numbers through a variety of mechanisms including aneuploidy. Through Dr. Kaplan’s research, we know that the diversity of speciation within the Potamogeton genus has also been presumably driven by aneuploidy and polyploidy. The exact mechanisms of how this evolution has been manifested are, as yet unknown. Thus, the significance of these hybrids, all of which have probably existed in their locations for centuries by reproducing vegetatively, can best be described as potentially containing the answers to questions that we don’t yet know how to ask.
Although one of the parents of the hybrid, P. foliosus, is widespread in Lake Runnemede, the other parent, P. zosteriformis, has never been found here. However, during the spring of 2021, I collected a floating specimen of P. zosteriformis in the wetland pond north of the western arm of the Lake. Since that wetland is separated from the Lake by a causeway and is upstream from the Lake itself, it is possible that the hybrid pre-dates the formation of the Lake during the 1860’s.
Hill’s Pondweed was first collected in Lake Runnemede in 1884 and has been found here sporadically ever since. It is quite similar to both P. foliosus and the hybrid, so it is possible that it is either missed (it really needs to be in fruit to positively be identified) or mis-identified. Either way, it is extremely rare in Lake Runnemede.
Several other Potamogeton species have been reported here at various times over the past century, including P. pusillus, P. strictifolius, P. perfoliatus, and P. natans. The first three are, like the current species, all linear-leaved and none are believed to be currently present. P. natans, which is a floating-leaved pondweed that is common in Vermont lakes and ponds, was noted here during the 1997 ANR survey, but has not been seen since. Many pondweeds are transported from lake to lake by waterfowl, but have a difficult time becoming established. The highly alkaline, hard waters of Lake Runnemede probably favor certain species of pondweeds over others.
The bottom line is that the plant formerly known as P. ogdenii, which is classified as a G1/SI critically imperiled species, is in fact an unnamed hybrid, found nowhere else in the world. However, none of this work is, as of yet, published. Dr. Kaplan’s research funding has been almost completely cut, and he has been moved to other projects within the Czech Academy of Sciences. Dr. Hellquist and his writing partner Garrett Crow are working on a revision to their two-volume Aquatic and Wetland Plants of Northeastern North America that will include the four hybrids, but it will probably be at least two years before that work is finished. In the interim, the Paradise Park Commission will continue to monitor and do our best to maintain the health of the plant and the Lake itself. We will continue to provide updates on the status of the hybrid and the Lake itself.
This information is extracted from our Paradise Park Management Plan (appendix G.), which can be found on the Town of Windsor website.
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