In this study, distyly was clearly confirmed in Polygonum criopolitanum Hance, which exhibited strict self-incompatibility. Unlike other distylous species, style-morph ratios of P. criopolitanum often deviated obviously from 1:1, and many populations were solely composed of long or short stylous flowers; the 1:1 style-morph ratio was occasionally found in very large populations. P. criopolitanum was dimorphic for intrinsic features such as style height and anther height and ancillary features

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... ch as pollen size and number. The L-morph flowers produced a significantly smaller and higher number of pollen grains than the S-morph flowers, and the stigma papillae of both morphs were not significantly different. We nearly found no seed sets in most wild populations and very low seed sets occasionally occurred in large populations, which was different from other species of Polygonaceae. Mating experiments showed that P. criopolitanum has a strict self-incompatibility system and clonal propagation was more common than sexual propagation, which was adaptive with the unisexual wild populations. Hygrocolous habitat, 20–60% soil water content, and height gap less than 4 m to the adjacent water were the main limiting factors for the distribution of P. criopolitanum.