Weedy rice produces a low number of grains per plant and is considered undesirable in cultivated rice fields. It spreads rapidly because of its high phenotypic plasticity and seed shattering. We used the RID14 marker to identify the genotypes governing red and white pericarp color in weedy rice. We then evaluated 18 characters of 199 weedy rice accessions (5 rice-growing regions in Asia) and 24 of cultivated rice as control, and analyzed them using coefficients of variation, principal component analysis, and cluster analysis. Our results showed that weedy rice accessions and cultivated rice populations from different regions of Asia were significantly different in one or more of their morphological characteristics. Weedy rice significantly differed from cultivated rice in plant height at vegetative growth phase, and in pericarp color and seed shattering during the reproductive growth phase. According to principal component analysis, weedy rice populations were significantly separated from cultivated rice in North China, Korea, Southeast Asia, Korea, and South China. We used principal component analysis and cluster analysis to categorize weedy rice populations into 3 main groups: Group 1 from Korea and Northern China; group 2 from Southern China and Southeast Asia; and group 3 from Eastern China. This study established an index for morphological characteristics of weedy rice to facilitate its identification the fields, which are expected to provide a theoretical basis for weedy rice infestation control in Asia.

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