Rice landraces constitute a core component of China's rice germplasm resources. Systematic identification and evaluation of their agronomic traits is of great significance for rice breeding. In this study， 218 rice landraces collected from 12 provinces south of the Yangtze River were used to evaluate 12 agronomic traits， including heading days， plant height， panicles per plant， and spikelets per panicle， under two environmental conditions， namely Sanya city in Hainan province and Huishui city in Guizhou province. The results revealed significant phenotypic variation in these traits between the two environments. The phenotypic values of traits including heading days， plant height， panicle length， spikelets per panicle， and seed setting rate were significantly higher in Huishui， which has higher latitude and altitude than Sanya. In contrast， panicles per plant and flag leaf width were higher in Sanya. Under the two different environments， thousand-grain weight， grain size and shape traits， and flag leaf width were relatively stable. Heading days， plant height， panicle length， seed setting rate， and flag leaf length were moderately stable， whereas panicles per plant and spikelets per panicle showed poor stability. Analysis of the coefficient of variation （CV） distribution for the 12 traits among the 218 materials revealed that over 89% of the materials exhibited high CVs for panicles per plant and spikelets per panicle， suggesting high environmental sensitivity. In contrast， more than 84% of the materials showed low CVs for thousand-grain weight， grain length-width ratio， grain length， and grain width， indicating that these traits were less influenced by environmental conditions. For heading days， plant height， and seed setting rate， approximately half of the materials were environmentally sensitive， while the other half were insensitive. Panicle length and flag leaf length in more than 66% of the materials were relatively sensitive to environmental change， whereas flag leaf width of 64.7% of the materials was relatively insensitive. The CV for heading days was lower in Indica landraces than in Japonica landraces， indicating better stability in indica landraces. Among them， Indica landraces from the Middle and Lower Yangtze River Rice Region showed the highest stability. Phenotypic comparisons between subspecies and across different growing regions showed that， indica landraces generally matured earlier， produced more panicles per plant， longer and more slender grains， longer flag leaves， higher seed setting rate， and higher thousand-grain weight. In contrast， japonica landraces had higher plant height， longer panicles， more grains per panicle， and wider grains. Landraces from the South China and Southwest China Rice Regions generally exhibited taller plant height， larger panicles， heavier grains， higher seed setting rate， longer grain length， and wider flag leaves， indicating higher yield potential. Cluster analysis revealed the closest genetic relationship between landraces from the South China and Southwest China Rice Regions， followed by those between the Middle and Lower Yangtze River and East China Rice Regions. Based on the stability of heading days， 20 broadly adapted elite landraces， including Huangsigu， Dalongnian， Beizinuo， and Shoutianjian， were identified. In addition， 20 accessions with superior yield-related traits， such as high grain number， large grain size， multiple panicles， or long grain shape， were selected. These elite landraces combine wide adaptability with outstanding yield-related characteristics and represent valuable parental resources for rice breeding.