The occurrence of tricotyledony has been reported in more than 15 dicotyledonous families and is mainly resulted from genetic variability, artificial selection and mutagenesis, and environmental stresses. Amaranthaceae species sand rice (Agriophyllum squarrosum) is a pioneer plant on moving sand dunes and wildly distributed in arid and semi-arid regions of the mid-latitude Asia. In the current study, tricotyledony was identified in two accessions and two elite lines derived from four natural populations of sand rice. The occurrence frequencies ranges from 0.83 to 14.29%. Tricotyledony correlates with variations of growth phenotype in different accessions. The tricotyledonous plant of Duolunbei was shown defect in seed development, whereas for Shigatse, tricotyledony was associated with significantly increased seed weight. Similarly, tricotyledony was also observed in two phylogenetically related species quinoa (Chenopodium quinoa) and spinach (Spinacia oleracea L.). These results indicate that tricotyledony is a widespread and conserved/convergent phenomenon across dicotyledonous species in response to extreme environments and/or internal genetic variation. To dissect the genetic architecture of tricotyledony, a chemical mutagenesis library was constructed where four pleiocotyledonous sand rice mutants were identified. Further functional characterization of these genetic loci will shed light on how the cotyledon number is canalized.