Growth and Dormancy in Talinum Rhizomes

Plants of Talinum calcaricum and T. mengesii (Portulacaceae) flower throughout the hottest, driest part of the summer on the rock outcrops where they are found, and die back to their rhizomes each fall. Once dormant, the rhizomes will not resume growth until subjected to a period of cold. Six to eight weeks 4° C were sufficient to end dormancy, and simple after—ripening would not substitute for cold. Sufficient cold is received in nature to end dormancy by mid—winter, and quiescene is thereafter environmentally impressed. The length of the growth period is apparently endogenously controlled, for dormancy ensues even when there has been no change in the environment during the entire life of the plant, and the length of the growth period is consistent under a variety of environmental conditions. The onset of dormancy in T. calcaricum occurs 23—34 weeks after rhizomes break dormancy or the seeds germinate. Both the length of the growth cycle and the requirement for cold treatment are in harmony with the natural environment of the two species.