Potamogeton epihydrus

Appearance

This is a perennial, rhizomatous herb producing narrow, compressed, unspotted stems to a maximum length of about 1 m. The stems are either unbranched or sparingly branched. It has two types of leaf. The submersed leaves are sessile 5–25 cm long and 0.1–1 cm wide, translucent, linear in shape and ribbonlike, red-brown to light green in colour with a blunt to acute tip. The floating leaves are similar to the floating leaves of other ''Potamogeton'', petiolate and opaque, up to 8 centimeters long and 3 wide.

The inflorescence is a small spike of flowers that arises from the water on a peduncle 1.5–5 cm.

This is a diploid species, with 2n = 26. Hybrids have been described with ''P. gramineus'', ''P. nodosus'' , ''P. bicupulatus'' , and ''P. perfoliatus'' .

Distribution

Ribbonleaf pondweed is predominantly a North American species, and is widespread in boreal and temperate North America. Its centre of distribution is the northeastern USA and southeastern Canada from the Atlantic to the Great Lakes, and on the Pacific seaboard from northern California to British Columbia. However, there are scattered populations in Alabama and Louisiana, Alaska, Wyoming, Montana and central Canada.

There are also two isolated populations in Britain, where it was identified as recently as 1944. The Outer Hebrides population is thought to be naturally occurring; there is also an accidentally introduced population in the Rochdale and Calder & Hebble Canals.

Status

Ribbonleaf pondweed generally grows in shallow, standing to slow-flowing standing and running waters at up to 1900 m altitude. It tolerates acid waters as low as pH 5 and has a preference for oligotrophic, soft water conditions. Nevertheless, liming experiments suggest that ribbonleaf pondweed is sensitive to severe acidification. ''P. epihydrus'' is a poor disperser relative to many other aquatic plants occurring in Connecticut lakes.

Ribbonleaf pondweed is generally common and widespread in North America. However, it is listed as Endangered in Indiana and Special Concern in Tennessee. In Britain it is Nationally Rare and listed as Vulnerable. British populations lack detectable genetic variation, suggesting a strong founder effect.

Habitat

Ribbonleaf pondweed generally grows in shallow, standing to slow-flowing standing and running waters at up to 1900 m altitude. It tolerates acid waters as low as pH 5 and has a preference for oligotrophic, soft water conditions. Nevertheless, liming experiments suggest that ribbonleaf pondweed is sensitive to severe acidification. ''P. epihydrus'' is a poor disperser relative to many other aquatic plants occurring in Connecticut lakes.

Ribbonleaf pondweed is generally common and widespread in North America. However, it is listed as Endangered in Indiana and Special Concern in Tennessee. In Britain it is Nationally Rare and listed as Vulnerable. British populations lack detectable genetic variation, suggesting a strong founder effect.