Abstract:Morphological indices of aboveground and underground organs of Plantago virginica were determined using Leaf Area Analysis System (FOCTA STD 1200P) and Root Analysis System (RHIZO STD 1600+) to investigate the influence of population density on the root morphology of the plant. The indices of aboveground organs included fresh weight, leaf number, leaf length, leaf breadth, leaf length-width ratio, leaf area, leaf perimeter, spike weight, spike number, spike length, inflorescence length and flower number.The indices of underground organs included root fresh weight,root length，project area,surface area，average diameter,root volume．The morphological indices of the root were divided into nine classes according to diameter size(O mm4.5 mm)．The relationships between the indices and the population density were regressively analyzed．The morphological indices which have obvious relationships with population density are leaf num ber,leaf area，leaf perimeter，individual flesh weight，spike weight，flower number,spike length，root flesh weight，root length，root surface area，and root volume．The results showed that the influence of population density on the indices of root morphology at different diameter classes were different，and the indices of root length，root surface area，root volume，and root project area of medium diameter size were more restricted by the population density.