Imbibition and Germination of Seeds of Colubrina oppositifolia (Rhamnaceae), a Federal-Endangered Tree Species Endemic to Hawaii

Abstract

Abstract Considerable variation in seed dormancy has been reported for Colubrina species. Most freshly-matured seeds of Colubrina oppositifolia have water-impermeable seed coats (physical dormancy). At 28(12 h)/20(12 h), 25(12 h)/15(12 h) °C and ca. 24 °C (room temperatures), 99–100% of the seeds imbibed, and 96–100% of the seeds that germinated did so in 27–34 days. Daily weighing of individual seeds showed that start of imbibition (= 5% increase in mass) at room temperature ranged from < 1 to 20 days. Thus, at high temperature, physical dormancy is broken so rapidly that technically most seeds would be classified as nondormant (i.e. germinate in ≤30 days). At 15(12 h)/6(12 h) and 20(12 h)/10(12 h) °C, 93 and 96%, respectively, of the seeds had imbibed after 30 days, but only 12 and 50%, respectively, of the seeds that germinated did so in 30 days. Eleven months of dry storage at room temperatures increased rates of imbibition and germination of seeds incubated at 28/20 and 20/10 °C. Based on the relativ...