PRATT, DONALD B.* AND LYNN G. CLARK. Department of Botany, Iowa State University, Ames, IA 50011-1020. - Amaranthus rudis and A. tuberculatus-- One species or two?
Amaranthus rudis and A. tuberculatus, the waterhemps,
are an important weedy, dioecious species pair, the identification of
which historically has been much confused. Morphological examination
reveals a large number of pistillate intermediates that fit neither
species and that staminate plants have not been well characterized.
Principal components analysis of isozyme data of waterhemps collected
from throughout the speciesí ranges shows that populations segregate
along a single geographic continuum that does not correspond with the
original morphological species designations. A single species,
Amaranthus tuberculatus (Moq. ex DC.) J. D. Sauer, is proposed.
Key words: Amaranthus rudis, Amaranthus tuberculatus, dioecy, isozymes