Variation in the factors determining flowering time in the Stellaria media complex

The effects of vernalization and photoperiod on flowering time were studied in Stellaria media (L.) Vill., Stellaria neglecta Weihe and Stellaria pallida (Dumort.) Pire collected from various habitats in Kyoto, Japan. Short- and long-day treatments had little effect on flowering in all strains of the three species. In two strains of S. media from riverside habitats and all strains of S. neglecta, the cohorts that were sown early in the autumn under natural conditions required a longer time to flower and had the first flower at a higher node position than the cohorts that were sown later. When grown in the greenhouse (minimum temperature >10 °C) these strains required a larger estimated thermal time than under natural conditions or did not produce flower buds at all, showing a requirement for vernalization. In comparison, most strains of S. media and all strains of S. pallida produced the first flower at almost the same node position independent of sowing time, and showed no requirement for vernalization. The strains of S. media from vegetable fields required a smaller thermal time than those from ruderal or semi-natural habitats. This observation was also true even after the non-agrestal strains had been adequately vernalized.