PRATT, DONALD B.*, LYNN G. CLARK, AND MICHEAL, D.K. OWEN. Department of Botany, Iowa State University, Ames, IA 50011. - Genetic characterization and phenetic analysis of weedy monoecious and dioecious Amaranthus L.
Amaranthus L. is a genus of approximately 70 species of
worldwide distribution with both monoecious and dioecious species. A
number of the monoecious species have long been an important component
of the world's weedy flora; twenty years ago, several Midwestern
American endemic dioecious species, including Amaranthus rudis
Sauer and A. tuberculatus (Moq. ex DC.) Sauer, became major
weeds. All genetic characterization of Amaranthus has focused
exclusively on the monoecious grain amaranths and their weedy
progenitors. Isozyme analysis of dioecious species reveals
fundamental differences in the genetic structure of populations of
monoecious and dioecious species. Monoecious species tend to have
very low within population diversity with most individuals fixed for a
single allele, indicating high levels of inbreeding. Dioecious
species have high within population diversity reflecting obligate
outcrossing. These species also form a phenetically distinct cluster
from the monoecious species.
Key words: Amaranthus, dioecy, isozymes, monoecy, weeds