SEED DORMANCY IN THE COLORADO PLATEAU SHRUB MAHONIA-FREMONTII (BERBERIDACEAE) AND ITS ECOLOGICAL AND EVOLUTIONARY IMPLICATIONS

Freshly-matured seeds of Mahonia fremontii collected in southern Utah in late July 1990 were used to investigate dormancy breaking and germi nation requirements. Seeds had fully developed spatulate embryos, and seed coats were permeable to water. Dormancy was broken by 6-10 weeks of cold stratification at a daily (12/12 h) thermoperiod of 5/1-degree s-C. Seeds germinated to 100% at 15/6 following 10 weeks at 5/1, and t hose kept at 5/1-degrees-C germinated to 97% after 14 weeks. Seeds do not require light for germination. A warm stratification treatment at 30/15-degrees-C for 3 or more days prior to cold stratification at 5/1 -degrees-C significantly increased germination. Seeds ''dispersed'' (i .e., added to the August to March sequence of simulated habitat temper atures) in August, September, October, November and December germinate d to 98-100% in March. Since gibberellic acid and afterripening in dry storage were somewhat effective in breaking dormancy and excised embr yos of 10-month-old seeds grew normally, seeds have inter-mediate phys iological dormancy (PD), a first report in the Berberidaceae. Seeds of Berberidaceae with PD are more advanced than other members of the fam ily with morphophysiological dormancy.