Seed Germination Ecology of the Rare Hemiparasite Tomanthera auriculata (Scrophulariaceae)

Seeds of the summer annual Tomanthera auriculata (Michx.) Raf. collected in Roane County, Tennessee, were dormant at maturity in October, and thus did not germinate when tested in light (14 h photoperiod) or continuous darkness over a range of (12/12h) thermoperiods from 15(day)/6(night) to 35/20℃. Cold stratification was required to break seed dormancy, and the optimum thermoperiod for germination of nondormant seeds was 15/6 or 20/10℃. Light was required for germination, and maximum germination percentages were obtained for seed samples that were both cold-stratified and incubated in light. Germination data from soil samples collected in the field in Roane County, Tennessee, and Adams County, Ohio, indicate that seeds can remain viable at population sites for at least 2.5 and 3.5 years, respectively. In a study with seeds collected in Roane County, Tennessee, 75% of those exposed to natural temperature cycles during burial in a nonheated greenhouse became nondormant during winter, and all of them re-entered dormancy in summer. During the second winter of burial, only 45% of the seeds became nondormant; however, ungerminated seeds were still viable. The dormancy breaking and germination requirements of T. auriculata are similar to those of some common, geographically widespread species, and thus do not appear to be related to its rarity.