COMPARATIVE ACHENE GERMINATION REQUIREMENTS OF THE ROCKHOUSE ENDEMIC AGERATINA-LUCIAE-BRAUNIAE AND ITS WIDESPREAD CLOSE RELATIVE AGERATINA-ALTISSIMA (ASTERACEAE)

Ageratina luciae-brauniae is endemic to sandstone rockhouses (semicirc ular recesses under cliff overhangs) in Tennessee and Kentucky and is closely related to the geographically widespread species A. altissima. At the time of normal maturity in September, 45-85% of A. luciae-brau niae achenes germinated in light and 0-22% germinated in darkness at 1 2/12 h daily thermoperiods of 15/6, 20/10, 25/15, 30/15 and 35/20 C. I n contrast, at the time of normal maturity in October, 0-53% of A. alt issima achenes germinated in light, and 0% germinated in darkness over the same range of thermoperiods. After 12 wk of cold stratification i n light at 5 C, 96-100% and 97-100% of the achenes of A. luciae-brauni ae germinated in light and darkness, respectively, over the range of t he thermoperiods, and after stratification in darkness, 73-100% and 34 -92% germinated in light and darkness, respectively After 12 wk of col d stratification in light at 5 C, 64-99% and 22-73% of the achenes of A. altissima germinated in light and darkness, respectively over the r ange of the thermoperiods, and after stratification in darkness, 55-99 % and 1-13% germinated in light and darkness, respectively. Peak germi nation of A. luciae-brauniae achenes sown in a greenhouse at near-natu ral temperatures in early October 1987 occurred in late October 1987, whereas peak germination of A. altissima achenes sown in late October 1994 occurred in mid-March 1995. Germination characteristics do not ex plain why A. luciae-brauniae is an endemic or why A. altissima is wide spread. However, they do suggest why achenes of A. luciae-brauniae cou ld germinate in rockhouses in autumn and why those of A. altissima do not germinate until spring.