Isoetes × truncata: a newly considered pentaploid hybrid from western North America

Abstract

Three Isoetes found in Pyramid Lake, Jasper National Park, Alberta, constitute populations of tetraploid (2n = 44)I. maritima, hexaploid (2n = 66)I. occidentalis, and an abortive-spored, pentaploid hybrid (2n = 55) with intermediate morphological characteristics. Although the hybrid has been present in the lake since at least 1918, I. maritima and I. occidentalis were previously unknown in Alberta. The presence of these aquatics hundreds of kilometres from their next known populations in central British Columbia is suspected to reflect the floristic and faunal affinity of the Pyramid Lake area to biotic regions in the interior of British Columbia. Morphological, scanning electron microscopy, and cytological data are provided to support our conclusion that the Alaskan type material of I. × truncata is synonymous with the Pyramid Lake pentaploid. Investigations of similar taxa in western North America detected several I. occidentalis populations in Alaska where it was previously unknown. This represents the first report of a pentaploid Isoetes hybrid in North America and the first western North American hybrid to be described in detail. Key words: Isoetes, Isoetes maritima, Isoetes occidentalis, Isoetes × truncata, hybrid, Alberta, Alaska.