Amaranthus rudis and A-tuberculatus - one species or two?

Waterhemps traditionally have been divided into two species, Amaranthus rud is and A. tuberculatus. based on morphology, but the distinctions break dow n for specimens collected from a major portion of the total waterhemp geogr aphic range. Two hypotheses of waterhemp species circumscriptions were expl ored using morphological and isozyme data sets. The first hypothesis holds that there are two waterhernp species as traditionally circumscribed. inter mediate morphological materials being hybrids. The second hypothesis holds that there is a single. polymorphic species of waterhemp. Principal compone nts analysis of pistillate morpho logical, staminate morphological, and iso zyme data sets all show a single waterhemp continuum exhibiting geographic variation. A single waterhemp species, A. tuberculatus. is proposed.