Observations were made in a sugar maple (Acer saccharum Marsh.) stand on the phenological response of three geophytes, Claytonia caroliniana, Erythronium americanum, and Trillium erectum, to solar radiation and temperature. The three species started development when the ground was partly covered with snow. The peak of the leafing and flowering stages occurred prior to the lead development of the maple canopy. Two of the geophytes, Claytonia and Erythronium, completed their life cycle prior to leaf development in the canopy. The life cycles appear to be strongly influenced by temperature and solar radiation.