Hill's pondweed (Potamogeton hillii) COSEWIC assessment and status report: chapter 6

Biology

Reproduction

Hill’s pondweed can reproduce both by seeds and vegetatively by winter buds. It flowers in late July and produces fruit in late August and September. Winter buds are produced in the fall. While Fernald (1932) claimed that winter buds were absent in Hill’s pondweed, both Haynes (1974) and Hellquist (1984) report their presence. No studies regarding the viability of seeds and winter buds have been published.

Hill’s pondweed can also form a rhizome-like structure if the stem becomes decumbent and subsequently covered in debris (Haynes, 1974). This results in rooting from the nodes; such newly rooted portions can become established as independent plants. Due to its manner of overwintering using winter buds and other asexual means of propagation, the species forms clonal patches (NatureServe, 2005).

Hill’s pondweed can hybridize with Potamogeton zosteriformis. It has been suggested that P. ogdenii evolved from such a hybrid (Hellquist and Hilton, 1983).

Survival

Pondweeds are consumed as food by waterfowl and mammals, though no studies have been published regarding consumption of Hill’s pondweed in particular. No information was found regarding offspring survival, population age structure and reproductive/recruitment rate.

Physiology

Hill’s pondweed is most closely associated with alkaline calcareous waters ranging from 53.0 to 316.7 mg/l HCO3- (Hellquist, 1980, 1984). It appears to be intolerant of pollution and turbidity (Hellquist, 1984). No information was found regarding climatic or other tolerance limitations.

Movements/dispersal

Most species of Potamogeton are wind pollinated, and dispersed by water or waterfowl (Sculthorpe, 1967). Winter buds would also be dispersed by water, and possibly waterfowl. Seeds could be dispersed through the digestive tracts of waterfowl (Haynes, 1974).

A summary of information on Hill’s pondweed in NatureServe (2005) indicates that “...seed dispersal to proper habitats is the critical reason for its apparent rarity”.

Considering the species’ endangered or threatened status in states adjoining Ontario and its overall rarity in the United States, it is unlikely that Ontario populations would be re-populated from propagules derived outside of Ontario.

Nutrition and interspecific interactions

Pondweeds, like other aquatic plants, provide habitat for aquatic invertebrates, food for waterfowl and mammals, and cover for amphibians and fish. No information has been published regarding the ecological role of Hill’s pondweed in particular, although presumably it would serve a similar ecological function as other narrow-leaved pondweeds.

Behaviour/adaptability

No information was found regarding the susceptibility of Hill’s pondweed to stress, disturbance, or other environmental changes.

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