Eupatorium rugosum Houtt (Ageratina altissima [L.] King & Robinson), commonly known as White Snakeroot, is a native, weedy, perennial that grows in shaded areas along margins of woodlands and waterways. Weedy plants often produce seeds that exhibit a wide range of variability in dormancy, thus allowing for the ecological flexibility to persist in different environments. Since this species is a hemicryptophyte (a rhizome producing over-wintering buds near the soil surface) there may also be variability in bud dormancy. This study identified Eupatorium plants with different levels of seed (achene) dormancy and examined the relationship of seed to vegetative-bud dormancy. Seeds from a single population (from Louisville, KY) were screened for differential germination-response to cold treatment, and then grown to maturity in the same environment. Following two cycles of recurrent selection, non-dormant lines showed an average of 74% germination prior to cold treatment (post-imbibition), whereas dormant lines only exhibited 17% germination before cold treatment. This difference was statistically significant. This recurrent-selection program is now in its fourth year, resulting in Eupatorium plants that produce seeds with highly-variable levels of primary dormancy. Therefore, it appears that there is a strong genetic component to the regulation of seed dormancy in this species. For the past two years we have observed that plants producing seeds with lower levels of dormancy tended to produce perennating buds that broke dormancy earlier in the spring than plants producing seeds with higher levels of dormancy. In March of both years, plants that produced non-dormant seeds had young shoots that were, on average, five times taller than the shoots from plants that produced dormant seeds. Perhaps some common regulatory elements control dormancy in both the seed and vegetative buds of this species.

Key words: Ageratina altissima, Asteraceae, bud, dormancy, Eupatorium rugosum, seed