Occurrence of the American Pondweed, Potamogeton epihydrus Raf., in the Hebrides

Abstract

IN August 1943, when I was dragging the lochs in the vicinity of Loch Eynort in the Isle of South Uist, Outer Hebrides, for pondweeds, there occurred in a backwater of Loch Ceann a'Bagh a very puzzling Potamogeton which, in its apparently sterile inflorescence, the paucity of its floating leaves and, in some plants, their total absence, strongly recalled × Potamogeton billupsii (= P. coloratus × P. gramineus), which I had discovered previously in Loch na Liane Moire in the neighbouring Isle of Benbecula. Nevertheless, the submersed leaves, in their general texture, lengths, breadths and parallel sides, were definitely against such an interpretation of the South Uist plant. Instead, they seemed to point clearly to a relationship with P. polygonifolius Pourr., or one of its hybrids. However, these ideas were in turn dispelled in 1944, when new and fruiting material was procured by Dr. W. A. Clark from a deep, peaty lochan draining into Loch Ceann a'Bagh. This enabled me to determine, with certainty, that both sets of plants belonged to the common American species Potamogeton epihydrus Raf. In this manner, not only was an important member added to the list of the American element in the British flora, but also a new species of pondweed placed on record for Europe.