This study investigated interspecific and site-to-site differences in the patterns of biomass allocation in two species of Lycopus with different modes of vegetative propagation. Lycopus americanus Muhl. produces belowground "stolons", whereas L. uniflorus Michx. produces surface "runners" with attached tubers. Both species commonly co-occur in wetland areas. Individuals of both species were harvested from a marsh and a floodplain site in northern Michigan at three times during the 1985 growing season, in order to determine seasonal patterns of reproductive allocation. In both species, flowering occurred earlier at the marsh site, and stolon and runner growth was initiated earlier at the floodplain site. Both species showed significant differences in both sexual reproductive effort (SRE) and vegetative reproductive effort (VRE) between the marsh and floodplain sites. For both species, final (i.e., September) SRE was greater at the marsh (16%) than at the floodplain (2-6%), whereas final VRE was greater at the floodplain (23%) than at the marsh (10%). Differences between species for final VRE were not as significant at either site. L. americanus had a signficantly higher SRE than L. uniflorus at the floodplain, but not at the marsh. Possible explanations for the large site-to-site differences in patterns of allocation will be presented.