A comparative study of the seed germination biology of a narrow endemic and two geographically-widespread species of Solidago (Asteraceae). 1. Germination phenology and effect of cold stratification on germination

Solidago shortii is endemic to a small area in northcentral Kentucky (USA), whereas two of its sympatric congeners, S. altissima and S. nemoralis, are geographically widespread. Seeds (achenes) of S. shortii(0.370 mg) are significantly larger (PLSD, P=0.05) than those of S. altissima (0.070 mg) and S. nemoralis (0.068 mg). Germination percentages of freshly-matured seeds of the three Solidago species collected in November 1991,1992 and 1994 were 0-2% in light at 15/6°C, 1-37% at 20/10°C, 9-56% at 25/15°C and 10-85% at 30/15 and 35/20°C. Stratification increased the percentage and rate of germination and decreased the time to the onset of germination (measured by Timson's index only at 20/10°C in light) in the three species. Following 12 weeks of cold stratification in light, seeds of the three species germinated to 72-100% in the light and to 22-100% in darkness over the range of thermoperiods; those cold-stratified in darkness germinated to 39-100% in light. Freshly-matured seeds of S. altissima and of S. nemoralis germinated to 0-4% in darkness, whereas those cold-stratified for 12 weeks in darkness germinated to 0-28% in darkness. On the other hand, freshly-matured and cold-stratified (in darkness) seeds of S. shortii germinated to 0-13 and 13-73%, respectively, in darkness. Under near-natural temperatures in a glasshouse without temperature control, germination of the three species peaked in March. Thus, the primary difference in dormancy-breaking and germination requirements of the three species is that the endemic germinates to a much higher percentage. In darkness than its two congeners. Seeds of S. shortii do not have any special dormancy-breaking or germination requirements that could not be fulfilled outside its present-day geographic range.