Isoetes in Alaska and the Aleutians

Abstract

Three species of Isoetes are recognized as present in the study area: echinospora Durieu (diploid, 2n=22), maritima Underw. (tetraploid, 2n=44) and occidentalis L.F. Hend. (hexaploid, 2n=66). Three interspecific hybrids are expected and two are known to be present: xpseudotruncata D.M. Britton & D.F. Brunton (triploid, 2n = 33) and Xtruncata (Eaton) Clute (pentaploid, 2n = 55). The missing hybrid taxon is echinospora (diploid) x occidentalis (hexaploid). The genus Isoetes was largely unknown in Alaska and adjacent areas until recent years. The floristic treatment by Hulten (1968) was a major advance at the time. He recognized three taxa in Alaska, muricata Durieu var. braunii (Durieu) C.F. Reed, muricata ssp. maritima (Underw.) Hulten, and truncata (Eaton) Clute. In the same publication, maritima ssp. maritima received syn- onyms of maritima Underw., macounii A.A. Eaton and beringensis Kom., whereas, truncata, had the query, I. asiatica with respect to Alaskan spec- imens, attached to it. Britton and Brunton (1993) considered Alaskan taxa in an assessment of the pentaploid hybrid xtruncata (A.A. Eaton) Clute in western North America. Further biosystematic studies on Alaska Isoetes are a natural extension of that hybrid investigation. Almost no cytological determinations of Alaskan taxa had been undertaken before Britton and Brunton (1993). Similarly, no Scan- ning Electron Microscope (SEM) studies of spores had been conducted. Britton and Brunton (1993) cited four Alaskan collections of occidentalis L.F. Hend., including a large collection by S. S. Talbot from Auke Lake that was deter- mined cytologically as 2n=66. Our objectives in the present study were to determine the number of species and interspecific hybrids of Isoetes in Alaska and to document their cytology, spore morphology, and distribution. Another longer term objective was to clar- ify the relationship of maritima with macounii and beringensis.