Isozyme variation in showy stickseed, a Washington endemic plant, and relatives
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Hackelia venusta, a rare plant endemic to Chelan County, Washington, USA, consists of two entities that differ most notably by flower colour and geographic location. We evaluated the hypothesis that these entities are separate species using a phenotypic analysis of isoenzyme variation to compare both forms of H. venusta with sympatric and allopatric populations of the closely related H. diffusa var. arida, and with the allopatric taxa H. diffusa var. cottonii and H. diffusa var. diffusa. Enzyme band phenotypes revealed that all populations were variable, with 60 to 80% polymorphic enzyme systems. Most variation was within population, with only 32% among population variation detected. The level of variation was moderate to high in H. venusta populations compared to other Hackelia populations. Enzyme band pattern data support the separation of H. venusta from H. diffusa. However, data do not provide evidence for the taxonomic separation of the two colour forms of H. venusta at the species level. Regardless of the taxonomic recognition of H. venusta colour forms, they should be conserved as rare extremes of Hackelia morphology and habitat preference.